FB/EK Holden Holley 350 Guide

FB/EK HOLDEN 350 HOLLEY CARBURETTOR ENTHUSIASTS GUIDE

REVISION

DATE

UPDATE

0

November 2011

Initial draft for review.

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Table of Contents 1 Background .................................................................................................................................................................... 3 2 Operation ....................................................................................................................................................................... 5 2.1 Fuel Inlet System ...................................................................................................................................................... 5 2.2 Idle System ............................................................................................................................................................... 6 2.3 Main Metering System............................................................................................................................................... 7 2.4 Accelerator Pump System ......................................................................................................................................... 8 2.5 Power Enrichment System ........................................................................................................................................ 8 2.6 Choke System ........................................................................................................................................................... 9 3 Capacity (CFM)............................................................................................................................................................ 10 4 Mounting ...................................................................................................................................................................... 12 4.1 Manifolds ................................................................................................................................................................. 12 4.2 Adaptor Plates......................................................................................................................................................... 14 4.3 Accelerator Linkage to Cable Modification .............................................................................................................. 14 4.4 Fuel, Vacuum and Choke ........................................................................................................................................ 16 5 Factory Specifications .................................................................................................................................................. 20 6 Assembly Diagram ....................................................................................................................................................... 21 7 Channels and Passages .............................................................................................................................................. 23 7.1 Metering Block (Float Bowl Side) ............................................................................................................................ 23 7.2 Metering Block (Main Body Side) ............................................................................................................................ 23 7.3 Main Body (Metering Block Side) ............................................................................................................................ 24 7.4 Main Body (Throttle Body Side) ............................................................................................................................... 24 7.5 Main Body (Choke Horn Side) ................................................................................................................................. 25 7.6 Throttle Body (Main Body Side) ............................................................................................................................... 25 7.7 Throttle Body (Manifold Side) .................................................................................................................................. 26 8 Disassembly and Overhaul Process ............................................................................................................................ 28 8.1 Kit Contents and Pre-disassembly .......................................................................................................................... 28 8.2 Special Tools........................................................................................................................................................... 30 8.3 Removal and Disassembly ...................................................................................................................................... 30 8.4 Cleaning and Inspection .......................................................................................................................................... 34 8.5 Assembly ................................................................................................................................................................ 35 9 Tuning.......................................................................................................................................................................... 39 9.1 Fuel Level ............................................................................................................................................................... 39 9.2 Idle Speed and Idle Mixture ..................................................................................................................................... 41 9.3 Fast Idle Speed ....................................................................................................................................................... 43 9.5 Main Metering Jets .................................................................................................................................................. 47 9.6 Power Valves .......................................................................................................................................................... 49 9.7 Venturi Sleeves ....................................................................................................................................................... 51 10 Troubleshooting ...................................................................................................................................................... 53 11 Modification ............................................................................................................................................................. 54 11.1 Fuel Supply Stability ................................................................................................................................................ 54 11.1.1 Wedged Float ..................................................................................................................................................... 54 11.1.2 Float Bowl Vent Baffle (Whistle) ......................................................................................................................... 54 11.2 Higher Air Flow........................................................................................................................................................ 55 11.2.1 Choke Horn Removal ......................................................................................................................................... 55 11.2.2 K&N Stubstack ................................................................................................................................................... 56 11.3 Automatic Choke ..................................................................................................................................................... 56 11.3.1 Automatic Choke Operation ................................................................................................................................ 56 11.3.2 Electric Choke Conversion ................................................................................................................................. 59 11.3.3 Hot Air Choke Conversion .................................................................................................................................. 61 11.3.4 Automatic Choke Tuning .................................................................................................................................... 62 11.4 Power Valve Blowout Preventer (Check Ball). ......................................................................................................... 64 11.5 Better Fuel Metering (Adjustable Metering Block) ................................................................................................... 64 12 Contacts .................................................................................................................................................................. 66

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1 Background This document aims to provide some information regarding fitment of 350 Holley carburettors to FB and EK Holdens. It contains:  historical information, such as which jets and bleeds were originally fitted to 350 Holley carburettors,  practical information on identification, disassembly and reassembly of 350 Holley carburettors, and  guidance on tuning, replacement parts and overhaul techniques. It contains answers to many of the questions that seem to come up routinely on most of the early Holden forums: “What jets should I run in my early Holden?” “Why is my Holley carburettor running so poorly?” “How do I set up a cable throttle?” Whilst this document is primarily related to the FB and EK Holdens, much of the information is applicable to other early Holdens. Please bear in mind that the 350 Holley carburettor was not an original fitment to early Holdens, and hence that limited documentation is known to exist. Much of the information below is drawn from internet forums, discussion with enthusiasts and common sense. I have used photos and other information from a wide variety of sources, particularly from the forums – if anyone is offended by my use of the material, feels I have breached copyright or needs recognition, please let me know and I will correct the issue immediately. I have drawn information from the following sources:  The Holley 2300 Handbook by Mike Ulrich (most notably the drawings used in Section 2),  Super Tuning and Modifying Holley Carburettors by Dave Emanuel,  Some very good info on how automatic chokes work and are tuned http://www.chevelles.com/techref/Adjusting_Automatic_Chokes.htm  Some info published online by Holley at www.holley.com.

from

Equally, I have made opinions and drawn conclusions on some of the information I have found and equipment I have owned, and have cross-referenced some material - if anyone believes that I have made an error (or knows a better way to do something), please let me know and I will update the document... after all, the main purpose here is to help other early Holden enthusiasts. I have marked some text in red in this document where I am missing information – any help in closing these gaps is appreciated. Like all things automotive, installing, operating and maintaining a carburettor comes with a risk. Leaking fuel lines can lead to fires, jammed throttles can lead to out-of-control vehicles and items dropped down a carburettor throat can cause massive engine damage (amongst other hazards). Any advice contained in this document is to be taken at the reader’s risk – qualified mechanics should be consulted where appropriate.

The 350 Holley is a common choice for Holden inline six-cylinder engines. Whilst the carburettor is oversized for the original FB/EK Holden grey motor, it is a good match for the larger displacement red motors. 350 Holley carburettors are also mandated in some forms of racing. For example, the current specification for both Australian Speedway Production Sedan and Modified Production Sedan classes

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mandates them for cars originally built in multiple carburettor or four-barrel carburettor form (though 3 13 allows the venturi to be milled out from the stock 1 /16” to 1 /64”). Having said that, Holley carburettors have a poor reputation amongst Holden owners. Some of the causes for this are:  Poor carburetor condition. Unfortunately, the average Holley has not been looked after too well, with a rebuild (either by a professional or by using a rebuild kit) strongly recommended,  Poor fuel atomisation, which can be resolved by installing venturi sleeves to increase fuel velocity, and  Poor fuel consumption, often caused by “over jetting” to try to hunt down the causes of the two issues above. Each of the issues above will be tackled in this document. 3

Holley has made a total of thirteen 350 CFM carburettors (all with 1 /16” diameter venturis), as per the table below: List number R3660 R4055-1 R4056-1 R4144-1 R4670 R4791 R4792 R7448 R80120 R80320-1 R80787-1 R82010 R87448

Model 2300 2300 2300 2300 2300 2300 2300 2300 2305 2300 2300 2010 2300

However, most Holley 350 CFM carburettors found on early Holdens are List number R-7448, as per the image to the right. I will focus on these carburettors, and will refer to them as “350 Holleys” for the remainder of the document. 350 Holleys are a Model 2300 carburettor. Model 2300’s have been made by Holley since the mid 1950’s, where they were used on Ford passenger car V8 engines. The 350 Holley is a non-staged two-barrel carburettor (where the two barrels open at the same time by a common throttle shaft). 350 Holleys can be identified by the List number, which is stamped onto the choke housing (see the red circle on the picture above). Below the list number will be four digits (e.g. 1662). The first three digits are the day the th carburettor was manufactured (in this example the 166 day of the year) and the last digit is the year (2 for 1972).

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2 Operation The 350 Holley carburettor has six basic systems that work together to provide the correct fuel/air mixture over different engine loads: • The fuel inlet system, which keeps a consistent level of liquid fuel “ready to go” in the carburettor, • The idle system, which controls the fuel/air mixture at no-throttle and slight-throttle operation, • The main metering system, which controls the fuel/air mixture at mid-throttle (or “cruise”) operation, • The accelerating pump system, which adds a small “shot” of fuel when you initially put your foot down, • The power enrichment system, which controls the fuel/air mixture at heavy throttle (hills, towing or race) operation, and • The choke system, which controls the air/fuel mixture for cold starting and warm-up. Each of these systems will be described below.

2.1 Fuel Inlet System The 350 Holley fuel inlet system consists of a fuel bowl, fuel inlet fitting, fuel inlet needle and seat, and a float assembly. Fuel from the fuel tank is fed via the fuel pump to the carburettor. A sintered bronze filter is usually installed in the fuel inlet fitting to capture dirt and rust and prevent them from blocking the fine passages inside the carburettor. If the bronze filter (and associated spring and gasket) are omitted, an inline filter must be used. If the fuel level is too low, the float (basically a hollow brass or plastic ball that floats on the fuel in the fuel bowl) drops down and opens the fuel inlet valve. This allows the pressurised fuel to enter the carburettor and begin filling the float chamber. Once the fuel level is high enough, the float rises, and closes off the inlet valve. The float chamber is vented by an internal vent tube to the air horn. This balanced pressure ensures that fuel/air mixtures stay constant even if the air filter is blocked by dirt. The level of fuel in the float chamber is adjusted by turning the adjustment nut and lockscrew on top of the float chamber (not shown in the simplified diagram). No disassembly is required to make this adjustment, unlike the original factory Stromberg carburetors which required the air horn to be removed. The fuel bowl on the 350 Holley carburettor is of the center-pivot type. This type of float is best for speedway, gymkhana or road racing where fuel sloshing is from side-to-side (an aftermarket wedgedshaped can also assist and will be discussed below). In drag racing applications, the front-to-back sloshing of fuel (and lifting of the nose of the car) can cause this type of float to not operate as effectively. A bumper spring under the hinge pin of the float helps to smooth out the float operation under stop/start operation.

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Note that there are three types of float construction: hollow brass (left image below), solid black nitrophyl (centre image below) and hollow white Duracon (right image below – the Duracon goes “pink” with use).

Brass floats are suitable for many different fuel types, but are unsuitable for blow-through forced induction systems (as the increased pressure may crush the float) or where dual-fuel is used (as the LPG flowing through the carburettor draws a substantive vacuum on the float bowl… and with the fuel inlet valve shut that vacuum can easily crush the float). Solid nitrophyl floats are used when there is a risk of crushing, though are not resistant to alcohol. Duracon floats are used as the factory-supplied float for new Holley carburettors, and may be susceptible to both crushing and alcohol.

2.2 Idle System Under very low engine speeds (idling), the engine does not produce enough vacuum to suck sufficient fuel from the main metering system (due to the near-closed throttle plate). However, under the throttle plate a high vacuum exists. This vacuum is used to pull fuel from the idle system. Fuel from the fuel bowl enters the main wells through the main metering jets that are screwed into the metering block. Some of this fuel is then bled off to an idle well. The amount which is bled off is limited by the idle feed restriction. The idle fuel is then mixed with air from the idle air bleed hole. The idle air bleed hole also determines when the idle system starts flowing fuel – the larger the idle air bleed, the slower the idle system is to start flowing. The air/fuel mixture then passes to the idle discharge port below the throttle plate where it is discharged, as per the diagram to the right. Idle mixture screws are located on the sides of the primary metering block. These control the volume of the pre-mixed air/fuel coming through the idle well. Turning the screws clockwise (in) will “lean” the idle system, whilst turning the screws counterclockwise (out) will “richen” the idle system. This part of the idle system is often referred to as “curb idle".

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The idle system also has a branch that delivers air/fuel mixture to a transfer slot above the throttle plate. When the throttle is closed (curb idle), there is little vacuum above the throttle plate, and the transfer slot does not flow. As the throttle begins to open, the transfer slot is uncovered, and vacuum draws fuel from it, as per the diagram to the left (the diagram looks like a second idle discharge hole, but it really is a vertical slot). The transfer slot provides fuel supply for the transition between curb idle and cruise (when the main metering jets take over). The more the throttle plate opens, the more of the transfer slot is exposed to vacuum, and the more fuel flows through the slot. Note that the fuel/air mixture flowing to the transfer slot is not altered by the idle mixture screws – the idle mixture screws only adjust the curb idle mixture.

2.3 Main Metering System The main metering system is designed to supply the leanest fuel mixture for cruising in the 35mph (60km/h) and over range. Fuel from the float bowl passes through the main metering jets and enters the main well. Here it is mixed with air from the main air bleed. The air emulsifies the fuel to allow easier vapourisation, and lowers the mixture viscosity for earlier feeding of the main metering system. The main air bleed hole also determines when the main metering system starts flowing fuel – the larger the main air bleed, the slower the main metering system is to start flowing. Engine vacuum pulls this air/fuel mixture and discharges it through the booster venturi. The booster venturi is located just above the main venturi, and acts amplify the vacuum applied to the main metering and power enrichment systems.

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2.4 Accelerator Pump System The accelerator pump system injects a small amount of fuel into the carburettor throat when the throttle is opened. The system provides good throttle response (sharp acceleration). When the throttle turns, a pump cam acts against a series of levers to move the pump diaphragm. The pump cam profile determines how fast and how much fuel is injected for each degree of throttle shaft rotation. The pump diaphragm moves upwards, closing the pump inlet check valve and opening the discharge check valve. Fuel is forced through a discharge nozzle and into the carburettor throat, hitting the outside of the booster venturi. When the throttle is released, the diaphragm moves back downwards under pressure of the return spring. The discharge check valve shuts, the pump inlet check valve opens and fuel is drawn from the float bowl to refill the pump, ready for the next “shot”.

2.5 Power Enrichment System When running under heavy load (high speed, towing, travelling up hills or racing), a richer mixture is required, which is supplied by the power enrichment system. 350 Holley carburetors utilize a vacuum operated power enrichment system. Manifold vacuum is connected to the power valve and holds the power valve piston shut. Under heavy load, the manifold vacuum decreases. When the manifold vacuum is low enough, it can no longer hold the power valve piston shut. The opening power valve supplies extra fuel through the power valve channel restriction to the main metering system.

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The vacuum level at which the valve opens can be tuned by selecting different power valves.

2.6 Choke System When starting a cold engine, a richer than normal mixture is required (because the slowlyspinning engine produces little vacuum to draw out fuel, and much of the fuel condenses on the cold inlet manifold walls). To do this, the choke valve is shut, restricting air into the carburettor. 350 Holley carburettors are fitted with manual chokes. A bowden cable operates the choke linkage, opening and closing the choke plate. The choke linkage also incorporates a fast idle cam. The fast idle cam bumps open the throttle a small amount when the choke is opened, increasing engine speed. The choke plate is offset and spring loaded, such that the plate opens slightly as the airflow increases (leaning the mixture).

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3 Capacity (CFM) There are some engine combinations where the original single-barrel Stromberg carburettor becomes restrictive. It is common practice for enthusiasts to go hunting for a larger carburettor in the search for more power… and sometimes that hunt finishes with a 350 Holley carburettor. Carburettors are often rated in terms of the amount of fuel/air mixture they can flow at a given manifold vacuum. The flow rate is expressed in cubic feet per minute, or CFM. Care needs to be taken though in that a given carburettor may have several different venturi sizes, and hence several different flowrates (for example the BXUV-2 1 3 carburettor was offered in both /32” and /32” venturi sizes for early Holdens). The manifold vacuum used to measure flow rate also varies. Some early published ratings for 1-barrel (e.g. B–Model Stromberg) and 2-barrel (e.g. WW-Model Stromberg and 350 Holley) carburetors were measured at 3” Hg. 4-barrel carburettors (for example Holley 4150 carburettors) were rated at 1½”Hg. This means that a 600CFM 2barrel does not flow the same as a 600CFM 4-barrel – the 4-barrel flows 40% more as it is tested at higher pressure drop. The table below has been compiled from information on multiple websites. I have converted the Quadrajet, Weber, and SU values to 3”Hg (they were published at 1.5”Hg). I have taken a single published figure for Stromberg BXOV-2 carburetors (210CFM) and converted to the smaller BXOV-1 and BXUV-2 carburettors by calculation based on the venturi and throttle bore diameters. The upshot of the above is that the table below is very approximate, but should give some indication of the relative flowrate achievable with different carburettors. Carburettor Weber 38-DGAS Rochester Quadrajet Mikuni 44 PHH Holley 7448 (“350 Holley”) SU HIF6 Weber 28/36-DCD SU HS6 Stromberg BOV-2 (the “big brother swap”) WW Stromberg Weber 32/34-DMTL Weber 32/36-DGV Weber 32/36-DGV Stromberg BXV-2 Stromberg BXUV-2 SU HS4 SU H4 Holley EGC Stromberg 48 Stromberg BXOV-1 Holley 94/8ba Stromberg LZ SU H2 Holley 94/59 Stromberg 97 Holley 92 Stromberg 81

Barrels 2 4 2 2 1 2 1

Venturi diameter 36mm/36mm 2¼ “/1.35” 37mm/30mm choke 3 3 1 /16”/1 /16” Variable 26mm/27mm Variable

1

1 /32”

2 2 2 2 1 1 1 1 2 2 1 2 2 1 2 2 2 2

9

28

28

1 /32”/ 1 /32” 26mm/27mm 26mm/27mm 23mm/27mm 5 1 /32” 3 1 /32” Variable Variable 1 1 1 /16”/ 1 /16” 1 1 1 /32”/1 /32” 3 1 /32” 15 15 /16”/ /16” 1”/1” Variable 15 15 /16”/ /16” 31 31 /32”/ /32” 7 7 /8”/ /8” 13 13 /16”/ /16”

Flowrate (CFM @3”Hg) 600 530 422 350 339 317 297 287 280 274 270 235 210 201 201 188 185 175 162 162 160 156 155 150 142 135

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Note that the chart below indicates the required carburettor capacity for typical early Holdens (around 80% volumetric efficiency). The blue line shows that a 350 Holley has sufficient capacity for even a 202ci motor running at 7500RPM.

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4

Mounting

4.1 Manifolds A number of manifolds are available to mount 350 Holley carburettors to early Holden motors. One of the most common manifolds used for early Holdens is the Redline Performance Torker II 2V manifold (part number 12-65M – see image to the right). This is a multi-fit manifold that can be used on 149-202 red motors and 2.85 or 3.3 blue motors.

Redline Performance also produced a Roadmaster manifold (see image to the right).

John Cain produced similar style manifolds for fitting 350 Holley carburettors to Holden red motors (see ® image to the right). AussieSpeed once manufactured Cain Manifolds, though the name was later dropped from their product line.

Lynx made a number of manifolds for fitting 350 Holley carburettors to Holden red motors, both in a style similar to the Redline and Cain manifolds (see image to the right), and in a long-runner format (see image to the far right. Unfortunately, Lynx are no longer producing manifolds. Firestreak made a water-heated manifold for 350 Holley carburettors.

A manifold was also produced with SS cast into it.

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®

Manifolds for fitting 350 Holley carburettors to early Holdens are also made by AussieSpeed . In 2009, negotiations started with Kit Cullan to buy the Holden 6 cylinder Cullan Special manifolds to suit red and blue motor 6 cylinder engines. After testing and looking at the changes and benefits in the newer style of ® inlet manifolds AussieSpeed had been working on, the Ultraflow pattern equipment underwent massive modifications and the Ultraflow name is no longer used. The following manifolds were made by ® AussieSpeed , but are no longer in production: ®

AussieSpeed part number AS0001 Holden 9-port 149-202 red motor. This manifold will work on a standard engine. Street and competition manifold with tall plenum, plenum divider, long sweeping runners for wider rev range, this is a smaller runner designed for maximum air speed, good torque and fast acceleration.

®

AussieSpeed part number AS0266 Cullen Special (Kit Cullan) Ultraflow Holden 9-port 179-202 and 208/218 stroker engines. The corresponsinf 12-port manifold is part number AS0267.

®

The current AussieSpeed manifold for red motor 9-port manifolds is part number AS0167 (below left) and AS0169 for 12-port heads. The design offers high port velocity and a divided plenum that feeds all runners equally.

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4.2 Adaptor Plates Whilst not ideal, it is also possible to reuse the factory inlet manifold, using an adaptor plate to mount the Holley carburetor flange (see dimensions below for various early Holden flanges).

350 Holley

Bendix Stromberg BX-Model

Bendix Stromberg WW-Model

The factory single-barrel Holden Stromberg manifolds are able to be used with an adaptor plate (e.g. Redline Performance part No. 10-501 for 149-186 engines, 10-502 for 202 or, 10-503 for late 202). Whilst operable, this setup has poor airflow, reducing performance. They suffer from fuel cone breakup which will allow the fuel to fallout and puddle rather than moving smoothly through the intake system. WW Stromberg manifolds are able to be used with a similar adaptor plate (e.g. Redline Performance part No. 10-187 or 10-233). The open nature of this plate has a far less disruptive effect on fuel flow.

For Varajet II manifolds, an adaptor plate is also available (e.g Redline Performance part Nº. 10-219). Varajet carburetors were found on WB Holden 202, UC Torana 1.9L, VC and VH Commodore 1.9L, 2.85 and 3.3L, and some VK Commodore 3.3L engines (some VK Commodores had Bosch LEII-Jetronic fuel-injection).

4.3 Accelerator Linkage to Cable Modification With some carburettor manifolds and linkages, it is possible to use the original FB/EK Holden throttle linkage (the swinging bar type) with a little bending. However, the 350 Holley carburettor is generally operated by converting the throttle linkage to a cable type, eliminating the complex linkage. A number of pedal/cable assemblies can be mounted into FB/EK Holdens, notably HZ Holden and Commodore. A neat (and simple) solution is to retain the original FB/EK pedal, and modify it to suit the cable from a Mitsubishi L300 Express van. These vehicles were sold from 1980-1986, and look similar to the photographs to the right. Note that the later models however do not have the required clevis at the cable end.

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The Mitsubishi L300 accelerator cable is quite long, and can be shortened with a simple pair of sidecutters to the correct length once installed. To undertake the conversion: 1. Remove all the throttle linkage except the pedal.  Remove the clip connecting the lower cross shaft operating rod to the accelerator pedal (under the car),  Unbolt the lower cross shaft assembly (four phillips-head bolts located under the car).  Remove the clip connecting the upper cross shaft operating rod to the upper cross shaft assembly. All the linkage from under the car should now fall out  Unbolt the upper cross shaft support (two phillips-head bolts per bracket, one bracket on drivers and passengers side of firewall.  Disconnect the throttle control upper rod from the carburettor. All the linkage from in the engine bay should now fall out. Don’t discard all the parts yet – the upper cross shaft support from the passenger’s side makes a good bracket for supporting the cable later. 2. Attach the Mitsubishi L300 accelerator cable clevis to the original Holden accelerator pedal, using the hole that the lower cross shaft operating rod mounted to (under the car). The cable can be attached with a pin and split pin, or by using a small bolt and nylock nut (do not overtighten the nut as it will bind the clevis).

3. The cable will now run into the cabin using the Mitsubishi L300 cable guide. You will need to drill a hole in the floorpan for the cable to pass through, and another two for the cable guide mounting bolts. Mount the cable guide using nuts, bolts and spring washers, with some sealant under the cable guide to prevent water ingress to the cabin. The photographs above show the mounting of the clevis and cable guide on a number of vehicles. 4. Run the cable inside the cabin, up the firewall (under the carpet/floor mat) and pass it out through the grommet where the original choke cable passes through. The picture to the right shows the cable routing with the carpet/floor mat removed. 5. The cable then passes across the engine bay to the carburettor throttle linkage. The cable must be mounted, similarly to the way that the choke tube holder assembly mounts the original choke cable (the photograph below to the right shows a holder

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assembly fitted to a Holley carburettor, and the photograph to the left to a twin Stromberg setup). 6. The cable setup often feels much lighter than the original throttle linkage, and an extra (or heavier) return spring can assist in returning the pedal feel. The photo below to the right shows a return spring mounted off a bracket on the original battery tray.

7. The cable assembly should be checked and adjusted so that the carburettor both achieves wide open throttle, and returns to idle. It’s a good idea not to cut the cable to final length until this has been done. In some cases, it may be necessary to extend the accelerator pedal lever (by welding on a piece of flat bar) in order to get enough pedal travel to attain full throttle.

4.4 Fuel, Vacuum and Choke The fuel connection at the inlet of the Holley 350 carburettor is located at a similar position to the original Stromberg carburetor for FB/EK Holdens. Provided the manifold chosen does not have long runners, it is possible with some gentle bending to get the original fuel line to align with the carburettor. The Holley carburettor inlet is AN-5 (SAE thread size ½-20) thread, as is the original FB/EK fuel inlet line. Note that the recommended fuel pressure for 350 Holley carburettors is 5-7 psi. Whilst standard GMH grey/red/blue motor fuel pumps (at 3.9 - 4½ psi) are adequate, care must be taken when an electric fuel pump has been added – the higher than required fuel pressure forces open the needle and seat, flooding the engine. The chart and table below provide some guidance. When using inline fuel pumps (notably Holley), a pressure regulator is mandatory to prevent flooding. Fuel Pump

Maximum Pressure (psi)

Free Flow (GPH)

Facet SS208 Facet SS171 Later Holden (blue motor steel can) Facet SS500 Facet 60104 Facet IP002 Early Holden (grey/red glass bowl) Facet SS148 Facet SS501 Facet SS165 Carter GP4600HP Facet STS504 Facet IP007 Facet IP131 Facet IP220 Facet 60106 Facet SS135 Carter GP4603HD

3½ 3½ 3.9 4 4 4 4½ 4½ 4½ 5 5 5½ 5½ 5½ 5½ 6 6 6

14 14 9½ 25 25 32 9 24 30 15 100 30 36 36 36 32 34 43

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Carter GP4070 Facet SS502 Facet STC505 Facet IP051 Facet RTW506 Facet BTP001 Facet BTP001 Carter GP4594, GP4389, GP4259 and GP4602RV Facet SS200 Facet SS503 Facet 60107 Holley Red Facet SS185 Facet 40222 Facet 40223 Facet 40237 Carter GP4601HP Holley Blue Holley Black

6 7 7 8 8 8 8 8 9 10 10 10 11½ 11½ 11½ 11½ 18 18 18

72 32 35 30 40 40 40 72 32 34 34 100 29 33 33 33 100 110 145

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160

140

120

Flow (GPH)

100

Holley red

80

Holley blue Holley black 60

Stromberg inlet pressure

40

350 Holley inlet pressure

Pressure regulator required to drop Holley red pressure down to 350 Holley 3-7psi inlet pressure range.

early Holden fuel demand

20

0 0

2

4

6

8

10

12

14

16

18

Prressure (psi)

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Increasing fuel pressure will also require the fuel level in the carburettor to be reset – as a rule of thumb, 1 every one psi of fuel pressure increase will raise the fuel level /32”. The 350 Holley carburettor has a number of vacuum sources: 3  full manifold vacuum, a /8” pipe located behind the throttle body provides vacuum for power brakes, vacuum windshield washers and PCV valves (if you have more than one of these, you will need to use plastic vacuum tees from an automotive parts store like SuperCheap or Repco). Full manifold vacuum is tapped off from below the throttle plates. You get more manifold vacuum when you take your foot off the throttle (this is why pre-EK vacuum wipers work so well when you lift your foot, but run poorly when you have your boot into it driving uphill in the pouring rain!). 3  timed spark vacuum, a /16” pipe located in the choke side of the primary metering block. Timed-spark vacuum (sometimes referred to as distributor vacuum) is taken from above the throttle plates. Timed spark vacuum is exactly the same as manifold vacuum – except that it is shut off under zero throttle (i.e. under idle conditions, there is huge manifold vacuum, but zero distributor vacuum). The strategy behind distributor vacuum (generally used in later-model carburettors) is to remove vacuum advance at idle, causing the vehicle to run hotter and combust exhaust emissions (often with the help of air injection systems at the exhaust manifold). Early Holdens were designed to run timed spark vacuum (the vacuum port connection is at the throttle body above the throttle plate – see diagram to the right). There is no harm in running distributor vacuum. However, for cars with large cams (high valve overlap and poor vacuum), tapping into manifold vacuum (and blocking off the distributor vacuum ports on both the carburettors) can give better vacuum signal at idle, more advance and hence better idling. This can also reduce engine temperature at idle. Note that 1 7 the original FB/EK vacuum line ends in a /8” NPT thread nipple (the nut is /16” AF). If using the full manifold connection, rubber vacuum hose can be clamped over both the original nipple and the 350 Holley manifold vacuum pipe. If the timed spark vacuum connection is used, it may be necessary to cut off the original nipple and use smaller diameter rubber vacuum hose to clamp to the (cleaned and smoothed) pipe end. Cap-off any vacuum source that is not used (plastic vacuum caps are available from automotive spare parts stores like SuperCheap and Repco from the same carousel that sells small blister packs of nuts and bolts). 350 Holley carburettors were originally fitted with manual chokes, which will connect directly to the original FB/EK choke cable.

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5 Factory Specifications The following table lists the factory (“out of the box”) specifications for the List number 7448 350 Holley carburettor:               

Model number 2300, List number 7448. 350CFM (@ 3”Hg) capacity. Intended as stock performance replacement for 2-barrel street applications. Also mandated carburettor for some oval track racing sanctioning bodies. 3 Venturi diameter 1 /16” (main body part number 6R1919). throttle bore 1½” (throttle body part number 12R-5174B, also stamped 7448 underneath). Throttle plates stamped 107. Throttle bore and shaft assembly part number 12R11070A. Manual choke. 30cc accelerator pump (accelerator pump cover part number 34R2178B) with “Orange” accelerator pump cam (part number 41R466) in position #2. Tube type discharge nozzle size 0.031” (part number 121-31). Viton® tipped adjustable needle with 0.110" seat (part number 6-504). #60 main metering jets with ¼-32 UNF thread (part number 122-61). Fuel bowl part number 134-103 (marked 36R4649B), with fuel bowl gasket part number 108-83-2. Centre hung float part number 116-2. Fuel inlet fitting tapped to AN-5 (SAE thread size ½-20) to suit 5 /16” OD tube. Metering block part number 134-203 with metering block gasket part number 108-89-2. Metering blocks stamped L7448 Single stage normal flow power valve opening at 8.5”Hg (part number 125-85). Power valve channel restriction approximately 0.056”. 3 3 One /16” timed-spark vacuum port (tapped from left side of metering block) and one /8” manifold vacuum port (tapped from rear of throttle body). Choke vacuum port (for fitment of hot-air or electric choke) controlled by a 0.055” (#54 drill) orifice screwed into the base of the throttle body. Ford automatic transmission kickdown, does not work with automatic overdrive transmissions. Renew Kit part number 37-1536, Trick Kit part number 37-933, Fast Kit part number 37-1543. WARNING: If you are using this carburetor with a GM overdrive transmission TH700R4 or a TH200R4, you must use a transmission kickdown cable bracket (Holley P/N 20-95) and stud (Holley part number 20-40). Otherwise, SEVERE transmission damage WILL result. This carburetor is not designed to work with ANY other automatic overdrive transmission.

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6

Assembly Diagram

Holley provides a generic assembly diagram for Model 2300 carburettors at http://www.holley.com/data/TechService/Technical/2300%20Exploded%20View.pdf, and for Model 2300 carburettors set up for 3x2 configuration at http://www.holley.com/data/TechService/Technical/2300%20(3x2)%20Exploded%20View.pdf. However, neither diagram maps out the 350 Holley carburettor very simply – both diagrams are generic, and have either extra or missing parts. I have taken both these diagrams and “cut and shut” them to make the 350 Holley assembly diagram below.

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No

Description

No

Description

No

1

Fuel bowl screw (4 off)

29

Metering body

57

2 3 4 5 6

Bowl screw gasket (4 of) Fuel inlet fitting Inlet filter gasket Inlet filter screen Inlet filter spring

30 31 32 33 34

58 59 60 61 62

7

Inlet fitting gasket

35

8 9

Fuel inlet check plug Check plug gasket Accelerator pump cover screw (4 off) Accelerator pump cover Pump diaphragm Diaphragm return spring Float lever shaft Float assembly Float spring Float shaft retainer Fuel valve seat lockscrew

36 37

Metering body gasket Power valve gasket Power valve Throttle body gasket Main body Pump discharge nozzle screw Discharge nozzle gasket Pump discharge nozzle

38 39 40 41 42 43 44 45 46

19

Lockscrew gasket

47

20

Fuel valve seat adjustment nut

21

Description Back-up plate stud nut lockwasher Stud nut Throttle body Pump cam lock screw Pump cam Curb idle screw spring

63

Curb idle screw

64 65

Throttle shaft bearing Throttle shaft centre bearing

Discharge nozzle gasket

66

Throttle shaft bearing

Pump discharge check valve Choke plate screw (2 off) Choke plate Choke shaft and lever Choke link seal Choke link Control lever nut Lockwasher Choke lever and swivel assembly

67 68 69 70 71 72 73 74

Fast idle cam lever screw Fast idle pick-up lever Fast idle cam lever spring Fast idle cam lever Throttle plate screw Throttle plate (2 off) Fast idle cam lever spring Fast idle cam lever screw Throttle body to main body screw (5 off)

48

Swivel screw

76

Adjustment nut gasket

49

Fast idle cam plate

77

22

Fuel valve assembly

50

Plunger spring

78

23

Fuel bowl gasket

51

Fast idle cam plunger

79

24

Fuel bowl assembly

52

25

Metering body gasket

53

26

Idle needle (2 off)

54

27 28

Idle needle seal (2 off) Main metering jet (2 off)

55 56

10 11 12 13 14 15 16 17 18

Fast idle cam and shaft assembly Back-up plate and stud assembly Choke rod lever and bushing assembly Choke spring Spring washer

75

Choke vacuum supply orifice Pump operating lever adjustment nut Pump operating lever adjustment spring Pump operating lever adjustment screw

80

Pump operating lever

81

Pump operating lever retainer

82

Throttle shaft and lever

83 84

Throttle return spring Choke housing screw (3 off)

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7

Channels and Passages

The images below illustrate the channels and passages cast and machined into the 350 Holley carburettor.

7.1 Metering Block (Float Bowl Side)

1. 2. 3.

locating dowels float bowl vent from float bowl to main body accelerator pump discharge from float bowl 4. main metering jet mounting holes 5. timed-spark vacuum port 6. power valve mounting hole 7. accelerator pump transfer passage from fuel bowl to main body 8. curb idle fuel passage from needle valve to main body 9. idle well 10. timed-spark vacuum passage 11. main well 12. gasket sealing bead

7.2 Metering Block (Main Body Side)

1. 2. 3. 4. 5. 6. 7. 8.

9.

10. 11. 12. 13. 14.

locating dowels float bowl vent from float bowl to main body curb idle discharge from needle valve to main body idle transfer fuel to main body timed-spark vacuum port power valve mounting hole accelerator pump transfer passage from fuel bowl to main body air bleed from main body to main well (approximately 0.0385” diameter) air bleed from main body to main well (approximately 0.027” diameter) timed spark vacuum port to nipple idle feed to idle well idle bleed air from main body idle down well main air well

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15. 16. 17. 18. 19.

power valve channel restriction (approximately 0.056” diameter) idle fuel from main well main fuel passage from main well to main body timed-spark vacuum passage gasket sealing beads

7.3 Main Body (Metering Block Side)

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

fuel from accelerator pump to pump discharge nozzle air from idle air bleed to metering block fuel emulsion to main discharge nozzle air from main air bleed to metering block float bowl vent from float bowl to main body vacuum from above throttle plate to timedspark port fuel emulsion to curb idle discharge hole fuel emulsion to idle transfer slot locating dowels fuel bowl vent to air cleaner fuel bowl/metering body/main body mounting holes air from idle air bleed to metering block not used (blanked hole) power valve vacuum chamber manifold vacuum from under throttle plates to power valve vacuum chamber

7.4 Main Body (Throttle Body Side)

1. 2. 3. 4. 5. 6. 7. 8. 9.

throttle body to main body mounting holes choke vacuum supply for hot air and electric chokes idle fuel emulsion to idle discharge hole below throttle plate transfer idle fuel emulsion to transfer slot above throttle plates timed-spark vacuum connection to hole above throttle plate on one barrel only manifold vacuum from under throttle plates to power valve not used – blind channel booster venturi not used – blind hole

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10. not used – hole through to airhorn, but no hole in throttle plate or throttle plate gasket

7.5 Main Body (Choke Horn Side)

1. 2. 3. 4. 5. 6. 7.

unused (blind holes) air cleaner stud mounting hole fuel bowl vent tube venturi booster venturi unused (blind hole) idle air bleed (approximately 0.035” diameter) 8. main air bleed (approximately 0.0775” (5/64”) diameter) 9. not used (blind holes) 10. fuel from accelerator pump to pump discharge nozzle

7.6 Throttle Body (Main Body Side)

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1. 2. 3. 4. 5. 6. 7. 8. 9.

throttle body to main body mounting holes transfer idle fuel emulsion to transfer slot above throttle plates idle fuel emulsion to idle discharge hole below throttle plates timed-spark vacuum connection to hole above throttle plate on one barrel only unused (blind hole) manifold vacuum from under throttle plates to power valve choke vacuum supply for hot air and electric chokes manifold vacuum port mounting holes for brackets (e.g. dashpot)

7.7 Throttle Body (Manifold Side)

1. 2. 3.

throttle body to main body mounting holes choke vacuum supply for hot air and electric chokes manifold vacuum from manifold to nipple

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4. 5. 6. 7.

manifold vacuum from under throttle plates to power valve mounting holes for brackets (e.g. throttle linkage or dashpot) unused hole mounting holes for brackets (e.g. throttle linkage or dashpot)

8.

manifold vacuum port

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8 Disassembly and Overhaul Process The following process describes the process of removal, disassembly and overhaul (often referred to as “putting a kit through”) for a 350 Holley carburettor.

8.1 Kit Contents and Pre-disassembly The 350 Holley carburettor overhaul illustrated below will be completed with a genuine Holley Fast Kit, part number 37-1543. Suits R4412, 4412-1, 4412-2, 4412-3, 7448, 9647, 84412, 87448. The kit contains the following parts:

1. 2. 3. 4.

5. 6. 7.

8. 9.

10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Metering body gasket – see note 1. Fuel bowl gasket – see note 2. Correct flange gasket. Incorrect flange gasket (not used for overhaul of 350 Holley carburettors). Paper gasket to seal choke air supply. Four plastic bowl screw gaskets. Rubber umbrella inlet (not used for overhaul of all 350 Holley carburettors). Two cork idle needle seals. Incorrect throttle body gasket (not used for overhaul of 350 Holley carburettors). Correct throttle body gasket. Incorrect 50cc accelerator pump diaphragm (not used for overhaul of 350 Holley carburettors). Correct 30cc accelerator pump diaphragm. Fuel filter. No. 65 power valve – see note 3. Fuel valve assembly. Inlet fitting gasket. Power valve gasket – see note 4. Fuel filter gasket. Adjustment nut gasket.

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20. Check plug gasket. 21. Lock screw gasket. 22. Pump discharge screw gasket. Plus two sheets of paper instructions. Note 1: the metering body gasket supplied in the kit is slightly different to the original Holley part. One hole is not stamped in the kit gasket (see red circle on the image to the right). However, this hole is not used in 350 Holley carburettors, and the kit gasket is acceptable to use.

Note that 350 Holley carburettors use no accelerator pump transfer tube. This means that the gasket on the left (set up for an accelerator pump transfer hole), as supplied in the kit, must be used. Use of a gasket like the one on the right will lead to internal leaks and poor operation. Note 2: the fuel bowl gasket supplied in the kit has two accelerator pump passages (the gasket is symmetrical). Some gaskets however only have one passage (see image to the right), and care must be taken that the gasket is put on the right way around – otherwise the gasket will cover the accelerator pump, and no pump shot will occur on acceleration.

Note 3: the factory 350 Holley power valve opens at 8.5”Hg (often referred to as an “85” power valve). The kit above (and most kits nowadays) supplies a valve that opens at 6.5”Hg (a “65 power valve). Power valves may be identified either from the opening setting being stamped into one of the valve nut flats, or onto the valve head as seen in the image to the right (which shows a 65 power valve).

Note 4: two different power valves are available for 350 Holley carburettors. The first (labeled “A” in the image to the right) has drilled holes in the valve, and a tanged gasket. The second (labeled “B” in the image to the right) has square “window” holes in the valve, and uses a circular gasket. The kit above (and most kits nowadays) uses the second type. Care must be taken to use the correct gaskets with the correct type power valve to avoid leakage.

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Prior to disassembling the carburettor, it is worthwhile checking for worn throttle shaft bearing areas. To do so, start the engine and leave it idling with the air cleaner in place. Spray some WD40 around the throttle body where the throttle shaft assembly passes through either side, using the red squirty straw on the can of WD40 to get at the right area. Make sure there is no grease or dirt around the area that could block the WD40 from getting to the throttle body. If the engine revs pick up, then the throttle shaft bearing areas are worn (letting in WD40 under vacuum to fuel the motor) and should be professionally rebushed during the rebuild.

8.2 Special Tools Most of the overhaul process can be undertaken with basic garage tools – screwdrivers, long nosed pliars, a set of imperial spanners and a 1” socket or spanner, a gasket scraper, some imperial drill bits and a set of feeler gauges. Whilst they are not critical, if you are overhauling a few Holley carburettors it is worthwhile buying a set of imperial feeler gauges and “narrow and bending” the 0.011”, 0.015” and 0.020” gauges – more on these below. A torque wrench calibrated in inch-pounds (not foot-pounds!) is also useful (not critical), though needs a slot-head screwdriver fitting (they are also useful for adjusting automatic transmission bands during servicing if you need an excuse to buy one).

8.3 Removal and Disassembly 1. 2.

3.

4. 5. 6.

7.

Remove the air filter, taking care not to drop the stud nut down the carburettor throat. Allow the engine to cool prior to disconnecting the fuel line at the carburettor fitting. Note that the fuel line may be under pressure from the fuel pump, and can leak some fuel – some rags to mop the fuel up or a steel drift to plug rubber fuel lines are useful. Disconnect the manifold vacuum hose at the rear of the throttle body base, and the timed spark vacuum hose at the side of the metering block. Plug off the disconnected hoses. Note that in some cases either or both of these hose connections may be not used, and may hence be capped off at the carburettor with plastic caps. Loosen the choke cable holder and swivel screw and disconnect the choke cable. Remove any throttle return spring(s) fitted. Loosen any throttle cable clamp fitted then disconnect the throttle cable (a throttle stud is often used). Undo the four carburettor to manifold nuts and remove them, taking care not to drop them down the carburettor throat. Lift the carburettor off the manifold studs, taking care not to bump any dirt down the manifold. Remove the manifold gasket then cover the manifold opening with clean rag. Undo the two slot-head screws and remove the choke cable holder bracket. Undo the remaining slothead screw and remove the choke lever and swivel assembly, fast idle cam plate and fast idle cam and shaft assembly as one unit.

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8.

Remove the choke link hairpin clip then remove the back-up plate and stud assembly, choke rod lever and bushing assembly and choke spring as one unit. Remove the paper gasket covering the choke vacuum passage (see red arrow on image to the right). Some carburetors have this passage filled with a lead ball – if a lead ball is present, do not disturb it.

9.

Turn the carburettor over and undo the phillips-head fast idle cam lever screw. Remove the fast idle pick-up lever, fast idle cam lever spring and fast idle cam lever as one unit.

11

10. Undo the /32” control lever and back-up plate stud nuts, and unscrew the slot head fast idle cam lever screw. Dissassemble the choke assemblies

Note that the choke link and choke link seal are not removed from the airhorn. To do so requires removal of the choke plate. This is quite an involved process (filing off the choke plate screws and restaking them on reassembly), and not generally needed for an overhaul. 11. To support the carburettor and prevent damage to the throttle plates/throttle body face, fit some spare ½” AF bolts into the flange holes. The bolts act as “legs”, supporting the carburettor off the workbench. Whilst the carburettor is together enough to get a good grip on it, loosen the fuel inlet fitting (1” AF) and fuel 5 valve seat lock screw and nut (slot-head/ /8” AF).

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12. Undo and remove the four slot-head fuel bowl screws. Separate the fuel bowl from the metering body – if the gasket is glueing the two together, a gentle tap with a screwdriver or hammer handle may loosen it. Retain the old fuel bowl gasket to compare to the new one from the kit.

13. Undo and remove the fuel inlet fitting (1” AF) and associated gasket. Pull out the sintered bronze fuel filter, fuel filter gasket and fuel filter spring (note that these are missing from the picture to the right). Unscrew the fuel valve seat lock screw (slot-head), remove the fuel valve seat adjustment nut and 5 unscrew the fuel valve assembly ( /16” AF). Remove the slot head fuel level check plug and associated gasket. Pick out the bowl screw gaskets (which have generally stuck to the fuel bowl), taking care not to damage the fuel bowl faces. 14. Undo and remove the two slot-head float shaft retainer screws. Remove the float shaft retainer, float lever shaft, float spring and float assembly as one unit. Take careful note of the relationship between the float shaft retainer, float lever shaft, float spring and float assembly before disassembling (see picture below right).

15. Undo and remove the four phillips-head accelerator pump cover screws. Remove the accelerator pump cover, accelerator pump diaphragm and diaphragm return spring. The hanging ball non-return valve and retainer (see picture below right) are not removed.

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Note that lateproduction 350 Holley carburettors used a “plastic umbrella” non-return valve. If one is fitted, remove and discard the plastic umbrella.

16. Separate the metering body from the main body – if the gasket is glueing the two together, a gentle tap with a screwdriver or hammer handle may loosen it. Retain the old metering body gasket to compare to the new one from the kit.

17. Unscrew the two main metering jets with a wide-blade slot-head screwdriver. Carefully remove the fuel bowl gasket, taking care not to damage the metering block face. Unscrew the two slothead idle needle valves and pick out the associated cork seals. Remove the power valve with a 1” AF socket. Carefully remove the metering body gasket, taking care not to damage the metering body face

18. Unscrew and remove the phillips-head pump discharge nozzle screw. Remove the pump discharge nozzle and associated gasket. Turn the main body upside down and catch the pump discharge needle valve as it falls out.

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19. Unscrew and remove the five phillips-head throttle body to main body screws. Separate the main body, throttle body and associated gasket. Remove the slot-head choke air bleed orifice from the base of the throttle body.

20. Unscrew the slot-head pump cam lockscrew and remove the lockscrew and pump cam. Undo and remove the accelerator 3 pump adjustment screw, nut ( /8” AF) and spring. Remove the pump operating lever retainer and slide off the pump operating lever. Unscrew the throttle stop screw and spring.

8.4 Cleaning and Inspection 1. Clean all parts in some petrol to remove most of the oil and dirt. Ensure good ventilation and no open flames when washing parts with petrol (or any of the solvents below). An alternative is to use one of the spray type “carburettor and throttle body cleaners” available from SuperCheap, Repco etc. Most of the cleaners available are made for spraying down a carburettor throat with the engine running, rather than detailed cleaning of a disassembled carburettor. They tend to be mainly solvent, evaporate very quickly, and are this not much use for “soaking” parts. They are also not very suitable for removing the carbon (“coke”) that builds up inside carburettors (what little they dissolve tends to restick as the cleaner evaporates). From trying some of them, I personally believe these spray cleaners are little (if any) better than using straight petrol for cleaning disassembled carburettors. Many forums recommend the use of “dip” cleaners to soak parts in (for example Berrymans B9 Chem Dip, which has a number of solvents, cresols and sodium bichromate). Some hunting has shown that “dip” cleaners are very hard to come by in Australia. One that is available is Yamalube Carburettor Cleaner, though I have not tried it. Paint thinners also does a fair job of removing the gunk. Note that the plastic choke link seal will be left in the airhorn – whilst it is tolerant of a short bath in petrol or thinners, soaking it for an extended period is not advisable. The same goes for the plastic pump cam. 2. Blow out all passages with compressed air in the opposite direction to normal flow. Do not rod-out any jets or passages with drills or wires unless absolutely necessary as it is likely to change their flow characteristics. If a compressor is not available, a bicycle pump (with a ball inflation needle fitted) will do the task. 3. Use a steel rule to check that the main body assembly, metering body and float bowl are flat where they join. Should any of these surfaces not be flat, replacement may be required. Whilst the main body can be machined flat (within reason), the metering body and float bowls each have gasket sealing beads. Machining these parts removes the beads, causing difficulty in gasket sealing.

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4. 5. 6.

7.

Check the idle discharge holes and transfer slots in the throttle body assembly to make sure they have no carbon deposits. Examine the idle needle valves. If they are ringed or grooved they must be replaced. Inspect the main metering jets to ensure they are clean and unmarked.

Check the float assembly for dents and punctures (for example the float on the left of the image is severely dented, either from being used in a blow-through forced induction system, a severe backfire, poor handling during reassembly or being used in a dual-fuel (LPG) vehicle).

8.

Check the throttle lever and shaft assembly where it passes through either side of the throttle body assembly (62) for looseness. Worn assemblies should be professionally rebushed during the rebuild. Check that the throttle valve opens and closes correctly. Check that the throttle plate screws are tight and staked. 9. Check the choke shaft assembly where it passes through either side of the air horn for looseness. Check that the choke valve assembly opens and closes correctly and that the choke plate screws are tight and staked.. 10. With the fuel bowl inverted, check the clearance between the accelerator pump check ball and the retainer bar. The clearance should be 0.0110.015”. Note that in order to do this a set of feeler gauges will need to be modified (narrowed and bent…a handy hint is to bend them first then file them narrow, as they don’t like being bent once they are narrowed). The retainer bar can be bent gently, though care needs to be taken not to pry the bar from its end fittings.

8.5 Assembly When assembling the carburettor, the bolts and fittings may be torqued. Whilst not absolutely essential, torqueing to a set value can prevent stripping threads (most of the screws are into alloy), or uneven tightening (leading to leaks). The following torque settings should be applied during assembly. Note that the values are in inch-pounds (not foot-pounds!). Application

Fastener SizeThreads Per Inch

Fuel bowl screws Main metering jets Fuel valve seat lock screw Float shaft retainer screws Fuel bowl inlet fitting Power valve Accelerator pump cover screws Choke vacuum restrictor grub screw Fuel level check plug Choke housing screws Pump discharge nozzle screw

12-24 ¼-32 ¼-32 6-32 7 /8-20 ½-28 8-32 10-32 5 /16-24 8-32 12-28

Torque Range Minimum-Maximum (inch-pounds) Dry Oiled 25-30 19-22 30-40 20-30 50-60 40-45 3-5 2-3 200-250 150-190 40-50 30-38 6-10 5-8 10-15 8-11 55-65 40-50 6-10 5-8 25-30 19-22

13. Install the pump cam and slot-head pump cam lockscrew into position #2 of the throttle shaft.

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3

14. Install the accelerator pump adjustment screw, nut ( /8” AF) and spring to the pump operating lever, leaving them loose for now. 15. Install the throttle stop screw and spring into the throttle body. 16. Fit and tighten the slot-head choke vacuum restrictor grub screw into the base of the throttle body. 17. Using the new throttle body gasket from the kit, fit together the main body and throttle body. Take care that the correct gasket is chosen from the kit. Tighten the five phillips-head throttle body to main body screws. 18. Fit some spare ½” AF bolts into the throttle body flange holes. The bolts act as “legs”, supporting the carburettor off the workbench. 19. Install the pump discharge needle valve. Using the new gasket from the kit, install the pump discharge nozzle and tighten the phillips-head pump discharge nozzle screw. Set aside the throttle/main body assembly for now. 20. Screw the two main metering jets into the metering block with a wide-blade slot-head screwdriver. 21. Using new cork seals from the kit, install the two slot-head idle needle valves into the metering block. Screw them in gently until they seat (do not overtighten!) then back them out 1½ turns. 22. Install the power valve and gasket (both from the kit) into the metering body with a 1” AF socket. Set aside the metering block assembly for now. 23. If the pump non-return valve is the “plastic umbrella” type, install a new “umbrella”. Wet the umbrella nipple with some spit, then insert the umbrella nipple from the outside of the fuel bowl and gently pulling it through from the inside. You will feel the nipple “click” as it seats. Cut the top off the nipple, leaving a small amount protruding into the fuel bowl (if the whole nipple is left it will interfere with the float at low float level).

24. Place the new diaphragm return spring into the accelerator pump housing. Fit the accelerator pump diaphragm from the kit over the spring, taking care to select the 30cc diaphragm from the kit. Fit the accelerator pump cover then install and tighten the four phillips-head accelerator pump cover screws. 25. Reassemble the float shaft retainer, float lever shaft, float spring and float assembly as one unit. Install the assembly into the fuel bowl, tightening the two slot-head float shaft retainer screws. 26. Install the new fuel valve assembly from the kit, using the adjustment screw and locknut gaskets from the kit. Install the fuel valve seat adjustment nut and the slot-head fuel valve seat lock screw. 27. Note that there are three types of float construction: hollow brass (left image below), solid black nitrophyl (centre image below) and hollow white Duracon (right image below).

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28. 29.

30. 31. 32.

33.

34. 35.

36.

37.

38. 39. 40.

 For brass and nitrophyl floats, turn the fuel bowl upside down, then adjust the fuel valve seat adjustment nut until the float sits in the middle of the fuel bowl (as per the image to the right). Tighten the slot-head fuel valve seat lock screw.  Duracon floats ride higher on the fuel than either the brass or nitrophyl float and, therefore, a higher setting is in order. For Durcon floats, turn 5 the fuel bowl upside down, then adjust the fuel valve seat adjustment nut until the float sits /16” from the bottom of the float bowl (the side with the adjustment nut), measured at the middle of the float (a drill bit is handy to measure with). Tighten the slot-head fuel valve seat lock screw. Install and tighten the slot head fuel level check plug, using the new check plug gasket from the kit. Assemble the main body assembly, metering block and fuel bowl, using the new fuel bowl gasket and metering block gasket from the kit. Whilst the fuel bowl gasket is normally symmetrical, the metering block gasket is not, and care must be taken that it is not put in back-to-front – check the alignment of the holes in the gasket with those in the metering block. Install and tighten the four slot-head fuel bowl screws, using the new plastic bowl screw gaskets from the kit. Fit the pump operating lever, screw, spring, locknut and retainer. Ideally, the accelerator pump operating lever should just be in contact with the short pump arm (mounted on the accelerator pump cover) at idle. This absence of slack gives sharp accelerator pump response. However, the accelerator pump operating lever needs to be set such that it does not overflex the pump diaphragm. To set the operating lever clearance, tighten the locknut such that the pump operating lever is just in contact with the short pump arm. Next, hold the throttle fully open, then move the pump arm until the pump diaphragm is fully flexed. Measure the gap between the pump arm and the pump operating lever adjustment screw with a set of feeler gauges. If the gap is less than 0.015”, back off the locknut to suit. This will mean that there will be a slight throttle response delay (due to the operating lever having to move a little bit before it contacts and starts to move the pump arm), but this is preferable to overflexing (and tearing) the pump diaphragm. Reassemble the three separate choke assemblies (fast idle pick-up lever, fast idle cam lever spring and fast idle cam lever as one unit, back-up plate and stud assembly, choke rod lever and bushing assembly and choke spring as a second unit and choke lever and swivel assembly, fast idle cam plate and fast idle cam and shaft assembly as a third unit. Install the fast idle pick-up lever, fast idle cam lever spring and fast idle cam lever as one unit and hold it in place with the phillips-head fast idle cam lever screw. Fit a new paper circle gasket from the kit to cover the choke vacuum passage. Holding the gasket in place, fit the back-up plate and stud assembly, choke rod lever and bushing assembly and choke spring as one unit. Install the choke link hairpin clip to the choke link. Install the choke lever and swivel assembly, fast idle cam plate and fast idle cam and shaft assembly as one unit. Install the single slot-head screw to hold it in place, then fit the choke cable holder bracket with it’s two slot-head screws. Adjust the fast idle screw with the choke fully open such that the gap between the throttle plates and the throttle bores is 0.020”. This is pretty small to measure with a set of standard drill bits, so again a “bent and narrowed” feeler gauge is handy. Set the throttle stop screw such that the throttle plates are closed, then back the screw out 1½ turns. Install the fuel filter spring, new sintered bronze filter and fuel filter gasket from the kit. Install and tighten the fuel inlet fitting (1” AF), using the new gasket from the kit. Before putting the carburetor onto the vehicle, it is wise to double check (triple check) that the parts that can fall through into the carburettor throat are staked and/or tight:

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41.

42.

43. 44.

45. 46.

47.

48. 49. 50.

 pump nozzle screw tight. Although the screw and nozzle cannot pass into the engine (won’t fit past the booster venturi), the pump check valve “needle” certainly can.  hot air choke restrictor grub screw tight.  Choke plate screws tight and staked.  Throttle plate screws tight and staked. Install the carburettor to the manifold using the new gasket from the kit. Do not tighten the flange nuts just yet as the ability to move the carburettor slightly makes some of the connections easier. 11 Note that the throttle bores are not centered on 350 Holley carburettors, and are offset 0.17” (~ /64”) to the back of the flange. If the carburettor flange gasket is put in back-to-front, it may catch the throttle plates, causing them to jam open Connect the choke control cable to the choke actuation lever, and mount the outer sleeve to the cable clamp. Actuate the choke cable through its full range of motion to ensure full choke operation and adjust as necessary. Connect the fuel line to the carburettor fitting. Connect the manifold vacuum hose at the rear of the throttle body base, and the timed spark vacuum hose at the side of the metering block. Note that in some cases either or both of these hose connections may be not used, and must hence be capped off at the carburettor with plastic caps. Install the throttle cable to the clamp and to the carburettor. Refit any throttle return spring(s) required. On automatic transmission vehicles only, install the transmission kickdown adjustment screw and black retaining clip, as correctly indicated. Failure to attend to this detail may result in a sticking wide-open throttle or dangerous uncontrolled engine speed. Tighten the manifold flange bolts to 15ftlb in the pattern shown in the image to the right. Do not overtighten the nuts, as a warped or cracked throttle body may result. Check that the throttle operates smoothly and returns to idle. Check that wide open throttle (WOT) is achieved. Start the engine and check the fuel lines and inlet fitting for possible leaks. Place the air cleaner gasket (not supplied in the kit) on the sealing flange, and install the air cleaner.

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9

Tuning

9.1 Fuel Level Fuel level is adjusted so that the vehicle does not run out of fuel (lean out) under cornering or acceleration (too low) or burp uncontrolled into the engine (too high). To set the fuel level: 1. 2. 3.

4. 5. 6. 7. 8.

Start the vehicle. Remove the fuel bowl sight plug. Observe the sight plug hole for the fuel level. If none is seen, the level is too low - fuel should be even with the bottom of the sight plug hole. If fuel comes pouring out of the sight hole, the float is set too high. To adjust the float level, shut down the engine. Loosen the lock screw on top of the fuel bowl just enough to allow you to turn the adjusting nut. Hold the screw in position with the screwdriver. 5 Turn the /8” AF adjusting nut in the appropriate direction: clockwise to lower float and counterclockwise to raise float. Turn the nut in increments of ¼ of a rotation. Retighten the lock screw. Restart the vehicle and observe the sight plug hole. Repeat steps 4. – 7. as necessary.

Note that there are a variety of Viton-tipped needle and seat combinations available for 350 Holley carburettors, ranging from 0.097” seat diameter to 0.110” diameter. Steel and titanium needle and seat assemblies (not recommended for street use but required for methanol use) are available up to 0.150” seat diameter. Installing too small a needle and seat means that the engine can starve under high load. Installing too large a needle and seat means that control over the fuel level will be more sloppy. The chart below shows the fuel flow through various needle and seat sizes at different fuel pressures. Note that for early Holdens (running at 3-6 psi of fuel pressure) there is no benefit in changing to a larger needle and seat size (even the 0.097” diameter seat will flow twice the early Holden fuel demand).

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50

40

Fuel Flow (GPH)

30 0.082" 0.097" 0.101" 0.110" (holes) 20

0.110" (windows) 0.120"

early Holden fuel demand

10

0

0

1

2

3

4

5

6

Inlet Pressure (psi)

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9.2 Idle Speed and Idle Mixture Engine idle speed (often referred to as “curb idle”, the speed the engine runs at when warm with the choke off) is adjusted so that the vehicle does not stall when stationary (too low) or consume excess fuel/jump when moving off (too high). Idle mixture is set to provide a good fuel/air combination (neither too rich nor too lean) when stationary. Whilst idle speed and idle mixture can be set “by ear”, there are some tools that make it easier/more consistent: 



A tachometer (either dash mounted or fed from the ignition leads) can help accurately set idle speed. If a tachometer is unavailable, a timing light can be connected and the number of “flashes” in twelve seconds counted. Multiply the number of flashes by ten to get the RPM. This is pretty hard to do though – you are looking to count around four flashes per second. A vacuum gauge (either dash mounted or a removable pressure gauge that screws into the inlet manifold after disconnecting the vacuum wipers (FB and earlier Holdens) or power brake/windscreen washers (NASCO accessories) from the manifold. The vacuum gauge gives a more accurate setting to the idle mixture than the “back it off until it runs smooth” method.

To set the idle speed and mixture: 1. 2. 3.

4.

5. 6.

Warm the car up to normal operating condition. Check the choke is off. Leave the air cleaner in place. Fit the vacuum gauge to a vacuum manifold port on the carburetor and the tachometer (where available). Adjust the curb idle speed screw until the engine idles at 480-520 rpm (check with a tachometer, timing light counting or “by ear”).

1

Adjust the two idle mixture screws /8 of a turn at a time, alternating between each screw. Turn them equally, until you achieve the highest possible vacuum reading without adjusting the curb idle speed screw. If a vacuum gauge is not available, use a tachometer (or your ear) to obtain the highest possible RPM. Check the engine speed again, and repeat steps 3. and 4. above until a satisfactory idle is achieved. Remove the tachometer and vacuum gauge and refit any vacuum lines that were disconnected.

If a rough idle persists after the mixture screws have been adjusted, check for vacuum leaks. These could result from unplugged vacuum fittings, carburetor flange gaskets that were torn during installation,

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cracked lines or loose bolt/screws. A quick way to check vacuum leaks is to spray WD40 in the suspected area with the engine running – if the engine speed increases, there is a vacuum leak. Note that on vehicles with very lumpy cams, the large amount of valve overlap can mean that there is very little vacuum at idle (6”Hg or less). At times, these vehicles may not respond well to setting the idle mixture – the idle mixture screw seems to do little to help the idle. The low engine vacuum at idle means that the throttle plates need to be opened more than usual to draw fuel from the idle system… in fact they can be opened so much that the idle transfer slots are uncovered, leading to excessively rich idle (and no control of the idle mixture as the idle needle valve only controls the lower idle discharge hole). To check for this, set the idle as best as possible, then remove the carburettor and check the throttle plate position – if more than 0.030” of the idle transfer slot is exposed, then this may be the cause of the loss of idle 1 control. One method to fix this is to drill a /16” hole in the throttle plate on the same side of the shaft as the idle discharge holes. The small hole will allow some air to pass, allowing the throttle plates to be 1 closed further and idle mixture control regained. The hole can be enlarged by stepping up drillbits in /32” increments until the throttle plates are sufficiently closed (don’t go too large or the throttle paltes will be fully closed, giving an off-idle flat spot). This condition should not be confused with an early opening power valve – see Section 8.8 below. For some vehicles, even with the idle mixture screws turned all the way in (lean), it may not be possible to obtain a satisfactorily lean idle mixture. In these cases the idle feed restriction may be closed up, or the idle air bleed enlarged. Modifying the idle feed restriction is preferred, as it does not affect the timing of the idle system. However, the 350 Holley idle feed restriction appears to be inside the idle tube, making this a difficult task. Whilst it is simple to “drill out” the idle air bleed, this will cause the idle system to start flowing later. Modifying the idle feed restriction and idle air bleed should not be taken lightly, and should be avoided where possible. Whilst early Holdens, being manufactured prior to July 1972, are generally not required to comply with emission standards. However, from that date onwards, all petrol passenger vehicles (and derivatives) were required, when new, to comply with a performance standard (ADR) that set limits for exhaust emissions of hydrocarbons (HC), oxides of nitrogen (NOx) and carbon monoxide (CO):   

ADR26 was introduced 1/1/1976, and captures the CO at idle test (limit of 4.5% maximum volume CO). ADR27, 27A, 27B and 27C applied to vehicles manufactured from July 1976 to January 1986. Vehicles made in this period generally ran on leaded petrol and employed carburettors. ADR37/00 covers the period from February 1986 to the present. Vehicles manufactured after January 1986 generally run on unleaded petrol (catalytic convertors), with computerized engine management systems, fuel injection.

A summary of the emissions requirements of each of the tests above can be found here: http://www.infrastructure.gov.au/roads/environment/impact/emission.aspx. Most early Holdens will not have to conform to the above. However, some engineers request the CO at idle test when vehicles have been modified to the extent that they require an engineer’s report. It is important to note that the idle test is normally done at idle (480-520rpm). There is an alternative “high idle” test, which is conducted at 2500rpm. This test, although usually not applied to early Holdens, will bring the main metering circuit into play (i.e. tuning for the CO at idle test is made via the idle needle valve (59), tuning for the “high idle test”, if it was ever applied, is by changing the main metering jet). To tune the idle circuit to meet a CO at idle test, an engine exhaust analyser is used – these are discussed more fully in Section 2.5.4 below. When tuning for emissions, a CO at idle reading of 1-3% should be targeted.

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9.3 Fast Idle Speed Fast idle is the speed that the engine runs at when the choke is on. To set the fast idle speed, 1. Start the engine, allowing it to reach operating temperature. Manually advance the throttle to just off idle. Push the fast idle cam up, so the fast idle screw is on the top step of the cam. This fast idle speed should be set to 1500-1600 RPM. 2. To adjust the fast idle speed, shut down the engine and hold the throttle in the wide-open position to expose the fast idle screw below the choke housing. Use a small ¼” open-end spanner for adjustment, turning the screw clockwise to increase the RPM or counterclockwise to decrease the RPM. 3. Start the engine, and recheck idle speed. 9.4 Accelerator Pump There are three different tuning parameters that may be modified to tailor the accelerator pump action (how the vehicle initially responds when you put your foot down): a) Pump discharge nozzle size, b) Pump cam profile (colour and position), and c) Pump capacity. The amount of fuel that can be delivered by one accelerator pump stroke is determined by the pump’s capacity and the profile of the pump cam. The period of time that it will take for this pre-determined amount of fuel to be delivered is affected by the pump nozzle size. 9.4.1 Pump Discharge Nozzle Size Holley accelerator pump discharge nozzles are stamped with a number which indicates the drilled pump hole size. For example, a pump discharge nozzle stamped “35” is drilled 0.035". Pump nozzle sizes are available from 0.025" to 0.052". Note that:  whenever a #40 (0.040)" or larger pump discharge nozzle is installed, the “hollow” pump nozzle screw should also be used. This screw will allow more fuel to flow to the pump nozzle, assuring that the pump nozzle itself will be the limiting restriction.  whenever a #37 (0.037") or larger pump discharge nozzle is installed, the 50cc accelerator pump should also be used. The following guidelines can be used to tune the pump discharge nozzle:  a vehicle that accelerates well at first then bogs down may be squirting all the fuel shot too quickly. The fuel shot can have it’s dutation extended by changing to a smaller pump discharge nozzle.  a vehicle which initially hesitates then accelerates smoothly (or gives a lean backfire) may need more fuel initially. This can be achieved by fitting a larger pump discharge nozzle.  when changing the pump discharge nozzles, jump three sizes at a time. For example if there is currently an off-line hesitation with a #28 (0.028") pump discharge nozzle, try a #31 (0.031") pump discharge nozzle. Once a pump discharge nozzle size selection has been made the accelerator pump system can be further tailored with the pump cam. 9.4.2 Pump Cam Profile and Position Holley offers an assortment of different pump cams, each with uniquely different lift and duration profiles. The cams are colour coded (see graph below), with the standard 350 Holley cam being Orange. The cams are available as Holley part number 20-12. Switching cams will directly affect the movement of the accelerator pump lever and subsequently, the amount of fuel available at the pump nozzle. The table below gives the speed with which each cam delivers fuel, which has been drawn from the first chart below. The second chart gives the fuel volume delivered by each cam.

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← Faster shot

Pink Black Green, White, Red and Orange Brown Blue Yellow

Whilst the table and charts gives some guidance, the best method of selecting the correct pump cam is by trial and error – monitoring either “seat of the pants feel”, quarter mile times or circuit elapsed times.

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0.15

0.1

0.05

0

0.2

0.25

Cam in position 2

Cam in position 1

Cam in position 2

Cam in position 1

Cam in position 2

Cam in position 1

Cam in position 2

Cam in position 2

Cam in position 2

Cam in position 1

Cam in position 1

Cam in position 1

Cam in position 2

Cam in position 1

Cam in position 1

Pump Volume (cc) 0.4

0.35

0.3

Pump Cam and Position

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Note that there are two holes in each pump cam, numbered 1 and 2. Placing the screw in position #1 activates the accelerator pump a little early, allowing full use of the pump’s capacity. Generally, vehicles which normally run at lower idle speeds (600-700rpm) find this position more useful because they can have a good pump shot available coming right off this relatively low idle. Position #2 delays the pump action, which is good for engines that idle at 1000rpm and above. Repositioning the cam in this way makes allowance for the extra throttle rotation required to maintain the relatively higher idle setting. In some drag racing applications, the vehicle is staged at considerably higher rpm. Where the full accelerator pump shot is required at the (high) staging rpm, the pump cam can be rotated such that the cam is at the start of lift at the staging throttle position. The cam holes are then redrilled for this new position. Note that pump arm adjustment and clearance should be checked and verified each and every time the pump cam and/or pump cam position is changed. 9.4.3 Pump Cam Profile and Position The standard 350 Holley accelerator pump is a 30cc unit. The larger 50cc unit should be used:  where a #37 (0.037") or larger pump discharge nozzle is installed,  where the brown or yellow pump cams are used (using the 30cc pump with these pump cams can cause the throttle to jam open). The 50cc accelerator pump is available as a bolt-on conversion kit (Holley part number 20-11). The main differences between the 30cc and 50cc pumps are as follows: Item 50cc 30cc Image (30cc on right)

Accelerator pump cover

Stamped 34R2773

Stamped 34R2178 B

Pump diaphragm

135-14 – deeper

135-12 shallower

Diaphragm return spring

4 coils

3 coils

7

Note that the pump diaphragm cover screws are /32” longer for the 50cc pump. The accelerator pump cover is thicker in the 50cc unit. This may necessitate the use of a ¼” (or thicker) spacer between the carburettor and manifold in order for the pump cover arm to clear the manifold. Another method used is to carefully grind a crescent in the inlet manifold to give the pump cover arm a slot to operate in.

9.5 Main Metering Jets Holley main metering jets are broached, flowed, and stamped according to flow rate. The stamped numbers are reference numbers and do not indicate drill size (for example, #88, #89 and #90 jets all have a 0.104” diameter hole). As Holley jets are widely available, there is no need to redrill a Holley jet (in any case,

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modification of the chamfers – see the image above left - on the jet by drilling can make the resultant jet flow very different rates to what would be expected). Holley main metering jets are available in sizes from #40 – #156. A higher relative number indicates a larger jet size. Standard main jets have a 3% tolerance in flowrates for a given jet size and approximately 4½% flow difference between jet sizes. A range of close-limit jets are also available with 1½% flow difference between jet sizes. Changing to a larger or smaller jet will either richen or make leaner the carburetor’s fuel curve from part throttle to full throttle, respectively. When changing the carburetor jetting, it is recommended to jump two jet sizes (e.g. change from a #60 to a #62 main metering jet). As there is only 4½% flow difference from one jet size to the next, changing one size won’t make that much of a difference. Listed below is a recommended jetting range for various Holden engine sizes using the 350 Holley carburetor. This jetting size is a good general guide only and will vary from engine to engine depending on the degree of modification. Engine Main jets Capacity Without venturi sleeves With venturi sleeves (Ci) 149 #55 #49 161 #57 #50 179 #58 #51 186 #60 #53 192 #60 #53 202 #61 #54 If a vehicle is changing operation to a higher altitude, air is thinner so decrease the jet size one number for every 2000’ (600m) increase in altitude.

There are a number of ways to select the correct main metering jet (or correctly adjust an adjustable main metering jet):   

reading the spark-plugs, measuring exhaust gas carbon monoxide, and running the car on a dyno/strip (more applicable to the power bypass jet – see below).

Each of these methods should be undertaken in conjunction with road testing, looking for stumbles, flat spots, drivability and fuel consumption. Reading the colour of the spark plug electrodes (and to a lesser extent the colour of the exhaust pipe) provides a cheap and easy guide to correct main metering jet choice. This technique involves driving the vehicle for a run (up to operating temperature and a moderate distance at “cruise” conditions – not all at idle or full throttle!). After stopping then cooling down the engine, each plug is removed in turn and the colour of its electrode compared. Today the use of unleaded fuels and high-energy ignition systems has made this method much harder because very little color is seen on the spark plug; however the pictures below give some guidance:

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Overly lean (main metering jet is too small). Whitish or pale deposits. May also be seen by erosion of the spark plug electrode or detonation damage of the insulator.

Correct jetting: electrode deposits are slight and not heavy enough to cause any detrimental effect. Colour is brown to greyish tan colour, and minimal amount of electrode erosion.

Overly rich (main metering jet is too large): Soft, black, sooty deposit.

A more full description of spark plug readings can be found at http://www.classiccarhub.co.uk/articles/spark_plugs.html. A much more accurate way to tune the main metering jets is to measure the carbon monoxide (CO) in the vehicle exhaust. CO is one of the gases in the engine exhaust (along with nitrogen (N2), carbon dioxide (CO2), water (H2O), hydrocarbons (unburnt fuel, often written as HC), and various nitrogen oxides (NOX) and sulphur oxides (SOX). The amount of CO in a vehicle exhaust is an indicator of the air/fuel mixture being supplied to the engine, and thus is an excellent way of tuning jet sizes on carburettors. Manufacturers typically specify a CO level somewhere within the range 0.5% to 3.5% by volume. At CO levels higher than this there is a loss in economy, and at very rich settings, typically 8% to 10% CO, the onset of poor running occurs, characterized by the particular engine sound that is known as “hunting”. It should be noted that an engine, even in good overall condition, will show a fluctuation in idle CO over a period of time, of typically 0.5%. To measure CO, a sample probe is placed into the exhaust pipe and an exhaust gas analyser unit “reads” the CO in the exhaust. The other readings that some exhaust analyzers provide include HC (the best mixture gives you the lowest HC), CO 2 (the best mixture gives you the highest CO2 reading) and O2. Whilst workshop units can cost in excess of $4000, a simple and cost effective exhaust analyser (the “Gastester Digital”) is available from Gunsen for around $250 (see http://www.gunson.co.uk/item.aspx?item=1835). This would not be a bad investment if you are planning to tune a few early Holdens over the years. Using this analyser, some starting points for tuning would be to tune to 0.75-1.25% CO (1–3% CO for a lumpy-cammed engine) at cruise conditions.

9.6 Power Valves There are two different parameters that may be set for the power enrichment system – the time (or vacuum) at which it comes on, and the amount of fuel which is flowed. The number stamped on a power valve, such as 65, indicates the manifold vacuum below which the power valve is operational. In this case, all manifold vacuums below 6.5” Hg, the power valve is operating. The factory “out of the box” power valve for 350 Holley carburettors is a standard-flow 85 (Holley part number 125-85). For most early Holden applications, a 65 power valve is suitable, provided

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the manifold vacuum is 12”Hg or higher. However, vehicles with a large overlap cam can idle at 6.0”Hg. At this vacuum, the power valve has opened and is starting to feed the mixture, leading to the vehicle “loading up” at idle. To correct this problem, install a lower-numbered power valve (e.g. a 55, 45 or 35 power valve). If the engine has a manifold vacuum of 12”Hg or less, a simple way to determine power valve size is take the manifold vacuum at idle and divide that number by two. The answer is the power valve size. For example a vehicle with an idle manifold vacuum of 9”Hg, a power valve of (9 / 2 =) 4.5 is reasonable. Holley power valves come in two different types – a standard flow and a high-flow. The high-flow power valves will flow more fuel, though it should be noted that the power valve does not usually control the fuel flow – the Power Valve Channel Restrictions (PVCRs) do. The following table gives the Holley power valves available: Part No. Flow Vacuum opening (“Hg) 125-1005 High 10.5 125-105 Standard 125-95 Standard 9.5 125-185 High 8.5 125-85 Standard 125-75 Standard 7.5 125-165 High 6.5 125-65 Standard 125-155 High 5.5 125-55 Standard 125-50 Standard 5.0 125-145 High 4.5 125-45 Standard 125-135 High 3.5 125-35 Standard 125-125 High 2.5 125-25 Standard 125-10 Standard 1.0

As indicated above, the amount of fuel which is flowed is determined by the PVCR. These are located in the metering block, and are able to be drilled to larger sizes to richen the fuel mixture under load. PVCRs which have been over-enthusiastically drilled and are too large can be reduced in size by inserting small vee-shaped lengths of wire into the PVCR. One method to tune the power valve (PVCR diameter and best vacuum opening point) is to use timed acceleration runs (e.g. ¼-mile times), or top speed/power (e.g. dyno-tuning). This involves trial and error jetting changes to obtain the best results, and needs some moderate track or dynamometer time to get decent repeatable results. An easier way is to again tune using an exhaust analyser (particularly if you have the Gunson exhaust analyser described in above). Some starting points for tuning would be to tune to 6.6% CO under load conditions. Whilst this could be reduced to 4% for engines with very good combustion chamber design, early Holden cylinder heads rarely meet this criteria. For vehicles that run wide-open throttle most of the time (like HQ Holden circuit racers), the power valve is often removed (blanked off with blanking plug part number 26-36) and the main jet sizes increased 6-8 jet sizes to suit. Whilst this is suitable for full throttle performance, it will lead to a very rich “cruise” condition and is not recommended for street use.

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If a vehicle is changing operation to a higher altitude, less vacuum is made by the engine so decrease the power valve setting 1.5-2”Hg for every 3000’ (900m) increase in altitude. Note that it is possible to damage the power valve by engine backfire. For carburettor built after 1992, a power valve blow-out protection system (a ball check valve is located in the throttle body, designed to be normally open but which quickly seats to close off the internal vacuum passage when a backfire occurs) is installed. Once closed, the check valve interrupts the pressure wave caused by the backfire, thus protecting the power valve. A kit is available to retrofit the power valve blow-out protection system to pre1992 350 Holleys – see below.

9.7 Venturi Sleeves Venturi sleeves increase air speed through the venturi, which help prevent flat spots and assists with low-down acceleration. Venturi sleeves should be used on Holden 149 and 161 engines when using a Holley 350 carburetor. Main jet sizes must be reduced when using these sleeves (see table above). It is also recommended to close up the two power valve channel restrictions in the metering block from 0.060” to 0.030”. This can be achieved by inserting bent vee-shaped wires or by fitting brass bleeds, though this can be a difficult process and it may be worthwhile putting up with a slightly rich power system for everyday (not race dedicated) use. Redline Performance venturi sleeves are available from American Auto Parts (part number 14-35) and Barnes Performance (part number BP14-35). The Redline Performance venturi restrictors are 0.035” thick 1 3 5 (~ /32”), and will change a Holley 7448 venturi diameter from 1 /16” diameter to 1.118” diameter (~1 /32”). The venturi restrictors are fitted into the top of the venturi (with the gaps over the booster venturis) and epoxied in place. The gap in the sleeve does not close up – it leaves a gap down the venturi wall. Note that venturi sleeves will slightly reduce the flow capacity (the 350 Holley is reduced from 350CFM to approximately 320CFM). To install venturi sleeves: 1. Whilst it’s possible to install the venturi restrictors with the carburettor still on the vehicle, there is a fair risk that you will drop something down the carburettor throat. It is strongly recommended that the carburettor be removed before fitting the venturi restrictors. 2. Clean the venturis and the outside of the venturi sleeves with some thinners to remove any coke, grease or fuel. 3. Unscrew the retaining screw and remove the accelerator pump discharge nozzle, screw and gaskets. 4. Place a small piece of PVC tape across the top of the accelerator pump discharge hole and another one across the four air bleeds. This will stop any stray epoxy falling into places it shouldn’t. 5. Drop the first venturi sleeve down past the choke plate. It’s a lot easier if the choke plate is removed, but not impossible (and restaking the choke plate screws is a pain in the bum). Resist the temptation to put the epoxy onto the venturi sleeve before dropping it in – there is a fair amount of twisting and wiggling to get the restrictors past the choke plate, which would get epoxy everywhere.

6. Turn the venturi restrictor around so that the slot lines up with the booster venturi, then push the restrictor into place (dummy fit). It should be a nice snug fit. The lip on the top of the restrictor stops it

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from pushing down too far down into the venturi (…or into the motor!).

7. Turn the carburettor over and use a screwdriver to gently poke the restrictor back out of the venturi, leaving it sitting on top of the booster/venturi.

8. Mix some epoxy, and using a cotton bud (or similar spreader) paint the outside of the venturi sleeve with epoxy. Take care not to get epoxy near the carburettor walls. Use only a thin smear of epoxy and don’t spread it too close to the edges of the venturi restrictor as it will smoosh out later. Avoid the temptation to fit and epoxy both restrictors at once… it is a fiddly process, easy to bugger up and the epoxy goes off quickly. 9. Push the freshly epoxied venturi restrictor into place. Check for any smooshed epoxy (or smears on the carburettor walls) and wipe it out while it is still wet. 10. Repeat steps 4 – 8 for the second venturi restrictor. 11. Allow the epoxy to set thoroughly. Remove the PVC tape and reinstall the accelerator pump discharge nozzle.

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10 Troubleshooting It is common knowledge that “carburettor” is French for “don’t F%@# with it”. Many Australian children have learnt to swear from listening to the carefully phrased epithets gently wafting from the open bonnet of an early Holden. The guidance below may assist in hunting down the cause of early Holden Stromberg issues (and perhaps prevent your children from developing their vocabulary). Of note, many ignition and timing issues are found to be the real cause of what is perceived to be a “bad carby” – the following table assumes all electrical and timing issues have been resolved.

Stalling (cold)

Power

Back fire (cold)

Surge

Acceleration

Hesitation

Economy

Hot Start

Flooding

Rough idle

Cause

Stalling

Problem

Incorrect idle adjustment Damaged idle needle Incorrect fast idle adjustment Idle passages blocked Metering jets loose or blocked Power valve loose or sticking Fuel inlet needle and seat loose or passing Float leaking, rubbing or level incorrectly set Gaskets leaking Pump discharge holes blocked Pump diaphragm worn or cut Pump check ball dirty or sticking Choke valve and linkage dirty, sticky or damaged Throttle valve loose, damaged or sticking Venturi dirty

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11 Modification

11.1 Fuel Supply Stability

11.1.1 Wedged Float For vehicles which are frequently turning under load (for example Speedway use and circuit racing), fuel can slosh to one side of the float bowl. The fuel acting on one end of the float causes it to rises, prematurely cutting off the fuel supply. To prevent this, a wedged float is available (part number 116-13). The wedged float is made from nitrophyl, and as the name suggests has a wedged shape. The wedge is designed so that as fuel sloshes up the side of the bowl, the fuel will ride up the wedge and allow the float to stay open and not close off prematurely. The wedged float is a bolt-in replacement for the original 350 Holley float.

11.1.2 Float Bowl Vent Baffle (Whistle) For vehicles which are under frequent acceleration (for example drag racing use), fuel can slosh to the rear of the float bowl and burp out the float bowl vent. This can lead to overly rich mixtures as the burped fuel is not metered. To prevent this, a float bowl vent baffle (often called a “vent whistle”) can be added to the metering block. The vent whistle (part number 26-89) extends the vent to the front of the float bowl, which is normally “dry” under hard acceleration. To fit the vent whistle, 1. 2.

3.

4.

5. 6.

7.

Remove and dissassemble the metering block. Insert the vent whistle into the metering block vent hole, protruding towards the float bowl side. Drill through the top of the metering block and the top of the vent whistle with a #51 drill (0.067”). Insert the supplied drive screw through the metering block and vent whistle. Ensure that the top surface of the vent whistle is not depressed (bent down) after installing the drive screw. Trim the end of the vent whistle so that it fits into the float bowl and has clearance to the front edge of the bowl. Check that the vent baffle has not sagged as it may contact the float, causing flooding. If it has sagged, stake the metering body underneath the baffle to raise it. Blow out the metering block with compressed air to remove any drill swarf before reassembly.

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11.2 Higher Air Flow

11.2.1 Choke Horn Removal One technique for squeezing more airflow (around 30-50 CFM) from a 350 Holley carburettor is to remove the choke air horn and blend the radius of the resulting edge. Whilst the process is simple, it does have it’s downfalls: Pro More airflow is gained (30-50CFM). Bonnet clearance is increased. Material cost is low.

Retains the 350 Holley carburettor (important where carburettor choice is restricted, such as in Australian Speedway Production Sedan and Modified Production Sedan classes)

Con The flow increase is small, and may be made more reliably by changing to a 500CFM Holley. The process is not reversible, unlike the use of a K&N Stubstack (see below). The flow increase may be detectable on a dynometer, but is not likely to be noticed “by the seat of the pants”. The change does not allow the use of the choke, making starting in colder locations difficult in winter. To get the full benefit, some epoxy needs to be added to the top of the carburettor air-horn. This may be susceptible to cracking off (and falling into the running carburettor throat) and hence required periodic checking.

The process is undertaken as follows: a) Disassemble the carburettor such that the main body assembly is bare. b) Scribe or stamp the List number and date code onto the underside of the air filter mounting plate (the next guy who tries to work out what the carburettor originally was will thank you for it). c) Hold the main body in a vice (using wooden jaws/packing to avoid marking the faces) and cut off the choke horn a few millimeters above the top of the main body with a hacksaw. d) Blend the top edges into the venturi with a die-grinder. e) Fill any resultant rough edges (including the now-redundant choke rod hole) with epoxy and sand smooth. f) Wash out any filings in petrol, then blow through all orifices and channels with compressed air.

Note that in the photographs above I have not shortened bowl vent – this can be brought down to 7 approximately /8” tall and mitred similar to the original. It is important to realize that the increased airflow gained from removing the choke horn can change air/fuel ratios – the carburettor should be retuned after installing one.

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11.2.2 K&N Stubstack An alternative to removing the choke horn in search of more airflow is to use the K&N Stubstack (K&N part number 85-021 for 350 Holley carburettors). The Stubstack is designed to increase the airflow of carburetors (typically 20-40 CFM, Hot Rod magazine's testing showed an increase of 28 CFM on a 650 Holley and 40 CFM on an 850 Holley, other testing has found 30 CFM on an 850 Holley) by decreasing the restriction around the choke horn. It reduces turbulence, improving metering accuracy. The Stubstack fits inside the air cleaner housing and slides snugly down over the choke horn. It is installed by loctiting into place on the choke horn whilst holding the air filter retaining nut finger tight. When installed on some models, there may be a slight gap at the base, however this is normal and will not affect performance. Due to space limitations between the choke horn and some air cleaner baseplates, the Stubstack has two thin spots in the casting. These will sometimes crack or chip slightly, but does not affect the performance. Whilst the Stubstack has been designed to work effectively with K&N Filtercharger™ elements and 360° custom air cleaner assemblies, many enthusiasts have found that it works equally well with other filters provided the minimum height above the stack is at least 1½" (preferably 2-3”), with best results obtained with large diameter filters of 4-5” height. This is not always possible with low bonnet clearances. It is important to realize that the increased airflow gained from installing a Stubstack can change air/fuel ratios – the carburettor should be retuned after installing one.

11.3 Automatic Choke 350 Holley carburettors came from the factory with manual chokes. The manual chokes fit well with the FB/EK Holden dash, as the original Holden choke knob and cable can be used to drive the 350 Holley choke and looks factory. However, for ease of driving it is possible to convert the choke to either electric or hot air. Whilst conversion to electric choke is the far simplest option, I will cover both electric and hot air chokes here for the sake of completeness.

11.3.1 Automatic Choke Operation Electric and hot air chokes operate almost identically – the only difference is the heat source they use. Just like the manual choke, the choke plate is connected by a link rod that passes down through the air cleaner mounting boss to the choke assembly. The rod is connected a choke housing lever. The lever is put under tension by a coil spring which holds the choke in the closed position when the coil spring is cold. If the coil is warmed up, it expands and slowly moves the choke housing lever/choke link rod/choke plate to the open position. The amount of tension in the spring determines how much heat is required to get the spring to start moving. The tension can be adjusted (by manually winding the spring up or down) by rotating the choke housing cap a few degrees either way. A series of marks on the cap show just how far it has been turned. One mark (the “index mark”) is normally bigger than the others and is used as the reference point. Rotating the cap anticlockwise to make the choke stay on longer is referred to as “richer”, whilst rotating the cap clockwise to make the choke open earlier is referred to as “leaner”. Both RICH and LEAN are cast into the choke

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cap as a reminder. The choke coil must be adjusted so that it opens the choke plate at the proper speed as the engine warms up - slowly enough to prevent lean stumbles; yet fast enough to prevent over-rich mixtures. The heat source for a hot air choke is the engine warmth. A small amount of air is drawn from a clean place, often by tapping into the air cleaner (the image to the right shows a Model 2300 carburettor where the air cleaner bosses have been drilled and a tube fitted to allow clean air to be drawn from the air cleaner). The clean air is then routed past a source of heat – often a choke stove in the exhaust manifold or inlet manifold crossover. If the engine is cold, the air is also cold, As the engine warms up, so too does the air flow. The “hot air” then passes into the choke housing past a small brass piston (we’ll come back to that small piston later) and past the coil spring. The “hot air” provides the heat to warm up the coil spring. The spent air then flows through a small vacuum port in the side of the carburettor (see red arrow in diagram to the right above). This port is present in all 350 Holley carburettors, though with manual chokes fitted the port is either covered with a gasket or is lead-filled. The air flows down a channel in the main body, through a channel in the throttle body and into the inlet manifold (manifold vacuum is used to “suck” the air along). A small screw-in brass restrictor (0.055” diameter or #54 drill) in the throttle body is used to control the rate of the air flow (the orifice is present in all 350 Holleys, including those with manual chokes – see red arrow in the diagram to the right). For an electric choke, the same air flow occurs, but the air source is not heated (it is often still drawn from the air cleaner, but does not pass through a hot air stove). Here the air flow is used to prevent the electric choke coil from burning out. Heat for the electric choke is supplied by electricity warming the coil (just like a toaster element). The electrical power is turned on when the vehicle ignition is switched on, starting to slowly warm and unwind the choke spring. Even when the engine is hot, the choke spring normally has power supplied to it. Without the air flow, the choke coil would soon burn out. The air flow path can be seen in the image to the right: 1. hot air enters the choke housing, 2. passes through a channel and into the main housing compartment, 3. flows over the choke coil (removed in this photograph) which warms the coil, 4. flows past the choke pull-off piston, 5. passes through a further channel, and 6. exits the choke housing to flow to the throttle body.

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Having the choke plate fully shut is fine for initial starting as it puts a lot of vacuum on the fuel system (at the low engine speeds developed by the starter motor there is precious little vacuum, so closing the choke plate helps conserve what little there is). However, when the engine first fires the vaccum available is much larger, and the engine requires to be fed some air. A fully closed choke plate will cause the engine to be overly rich, and can stall or flood. To prevent this, the choke plate is cracked open slightly as soon as the engine fires. This is done by the small brass piston mentioned above, called the choke pulloff. The choke pull-off has the air flowing past it for the choke supply. At low engine speeds (when the starter motor is turning) there is not enough vacuum (and hence not enough air flow to the choke) to move the small brass piston. Once the engine fires, vacuum increases (as does air flow to the choke). This causes the choke pull-off piston to move, overriding the choke coil spring and cracking open the choke plate. After a minute or so of operation, the choke coil spring has warmed up and opens the choke plate even more, making the choke pull-off redundant. Note that the choke pull-off piston only just cracks the choke plate open – if it opens too much, the engine could hesitate, backfire through the carburettor or stall from having too little choke function. The amount the choke plate is cracked open by the choke pull-off is adjustable, often by bending a linkage rod or by an adjustment screw. The choke pull-off can be seen in the image to the right. The choke linkage also incorporates a fast idle cam (the red plastic item in the image to the right). The fast idle cam bumps open the throttle a small amount when the choke is opened, increasing engine speed. The fast idle cam has a number of “steps” that are ridden by the fast idle screw. As the engine warms and the choke closes, the fast idle cam rotates, the fast idle screw drops down to lower “steps” and the throttle closes back to the curb idle speed. When the choke pull-off cracks the choke plate open, pushing the accelerator pedal allows the cam to rotate so that the fast idle screw will drop from the highest (fastest) step and align with the second highest (second fastest) step of the fast idle cam. Note that adjusting the choke pull-off may also change the fast idle cam position and vice-versa. If the vehicle has flooded, the spark plugs will be wet and will prevent the engine firing. If the accelerator pedal is pushed all the way to the floor (and held there), the throttle will rotate open ready to let lots of lean fuel/air mixture in to dry the plugs. However, the closed choke plate will prevent this air getting in. To accommodate this, the fast idle cam lever has a small unloader tang on one side. By pushing the accelerator pedal all the way to the floor, the rotating throttle shaft rotates the fast idle cam lever, the tang moves forward and butts up against the end of the “steps”, pushing the fast idle cam partly around. This drives the choke plate manually open (not all the way, but a little bit more than the choke pull-off would open it). This allows the airflow in to clear the flooded engine. Releasing the throttle allows the choke spring (or choke pull-off) to resume controlling the choke plate position.

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11.3.2 Electric Choke Conversion An electric choke kit is made by Holley (part number 45223) to replace the manual choke. The kit supplies the following parts: a) short black earth lead, b) long red (sometimes black) 12V positive lead, c) thermostat housing gasket d) thermostat housing clamp e) thermostat housing assembly f) choke housing assembly g) choke link h) fast idle cam lever i) fast idle cam lever spring j) choke housing gasket k) choke link retainer l) choke housing screws m) fast idle cam lever screw n) thermostat housing clamp screws To install the electric choke kit: a) Remove the carburetor from the vehicle. b)

Remove the three choke housing screws securing the manual choke housing assembly to the main body. Remove the choke link retainer from the choke link and the manual choke backing plate. Keep the retainer for use at a later time.

c)

Remove the fast idle cam lever screw. Remove the fast idle cam lever and fast idle pickup lever and fast idle cam lever spring. Retain the screw, spring, and small pickup lever.

d)

Pull the choke housing gasket off and discard it. If the choke vacuum passage has been lead-sealed, carefully drill through the lead (with a drill in a hand chuck) then pick out the hollow ball. Thoroughly clean the mounting surface of the gasket. Blow compressed air through the passage from the bottom of the throttle plate up to make sure the passage is free of blockages. Air should exit from the choke passage.

e)

Use the new fast idle cam lever from the kit and the screw, spring, and small pickup lever retained above, as

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shown in the figures below. Assemble the parts onto the throttle shaft.

f)

Moisten the cork choke housing gasket provided in the kit. Attach it to the vacuum passage hole on the choke housing assembly. Insert the choke rod through the hole in the lever on the back of the choke housing. Make sure the fast idle cam is above the choke rod. Use the fastener clip retained above to secure the rod to the lever. Position the choke housing assembly to the carburetor main body. It will help to open the throttle slightly to clear the fast idle lever away from the fast idle cam assembly. Note that on most applications, the original choke link will be used. However, on certain carburetors the new choke link supplied with the kit may have to be used.

g)

Using the three equal-length long choke housing screws from the kit, secure the choke housing assembly to the main body. Manually operate the choke plate by moving the bi-metal pick-up lever on the front of the choke housing assembly. The choke plate should move freely. If not, check the choke linkage to make sure there is no binding and that the fast idle screw is in alignment with the cam on the back of the choke housing.

h)

Install the new thermostat housing gasket onto the thermostat housing.

i)

Install the thermostat housing and thermostat housing clamp. Install the clamp so it bows outward from the housing as per the image to the right. Ensure the bi-metal pick-up lever (in the housing) fits into the loop on the bi-metal spring. Check this by turning the housing in both directions. The choke plate should open when rotated clockwise, and it should close when rotated counter-clockwise.

j)

Using the three equal-length short thermostat housing clamp screws from the kit, fasten the clamp and thermostat housing to the choke housing assembly. Tighten it enough to hold the thermostat housing in place, but still allow it to be rotated.

k)

Rotate the thermostat housing until the mark on the housing aligns with the index on the choke housing assembly. Tighten the clamp screws so the housing cannot rotate. Do not block the fresh air intake.

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l)

Correct polarity must be observed when connecting the electric choke wires. Connecting the (+) lead to earth and the (-) lead to a 12V source will result in a direct short and could cause a fire. Use the shortest wire from the kit to connect the bayonet end to the thermostat housing negative terminal marked (-). Ground the eyelet end to the carburetor. Do this under a screw securing the choke housing assembly to the main body.

m) Remount the carburetor on the vehicle. Connect the long wire from the kit to the thermostat housing positive terminal marked (+). Run the other end of the wire through the firewall using an existing grommet. Connect is to an ignition activated 12V source so that the choke cap only gets voltage when the engine is running – for FB/EK Holdens, this is the from the fuse panel (located under the dash on the driver’s side) via the 15 amp turn signal/heater/backup fuse (the lower one on the picture to the right) at the back of the panel. A blown choke fuse will disable the heater fan, indicators and reverse lights (each of which were either options or standard on FB and EK Holdens). The choke power lead will require a female spade connector on the end to connect onto the male terminal blade at the rear of the fuse panel (a simple push on fit as the male terminal is already present in all FB/EK Holden fuse panels). It is recommended that insulated terminals are used, as many of the FB/EK wiring terminals are bare, and easy to short. Double check with a voltmeter or test light that the choke only has power when the ignition is on. Note that it is not recommended to use the 12V side of the coil for the power source, as it will result in unacceptable choke operation, and could cause engine misfiring, resulting in possible engine damage. If the vehicle has an aftermarket oil pressure switch (for example driving an electric fuel pump), it would be even better to route the power through that switch – that way the choke only gets power once the engine has fired (and has oil pressure), and does not get power (and start opening) if the vehicle is hard to start and cranking for a long time. n)

Start the engine, allowing it to reach operating temperature. Manually advance the throttle to just off idle. Push the fast idle cam up, so the fast idle screw is on the top step of the cam. This fast idle speed should be set to 1500-1600 RPM. Shut down the engine, and hold the throttle in the wide-open position to expose the fast idle screw below the choke housing. Use a small ¼” open-end spanner for adjustment, turning the screw clockwise to increase the RPM or counterclockwise to decrease the RPM. Start the engine, and recheck idle speed.

o)

Choke tuning adjustments are listed below. After making final adjustments, start the engine and make sure the choke plate opens completely.

11.3.3 Hot Air Choke Conversion Whilst a genuine kit is not available, it is possible to fit the 350 Holley carburettor with a hot-air choke from another Holley carburettor. This tends not to be a common modification though, as it is easier to source a 12V power source for an electric choke than it is to tap a hot air source. The hot air choke operates similarly to the electric choke described above, with a coiled spring being connected to the choke rod. When the engine is cold, the spring holds the choke plate closed. A flow of air is drawn into the choke housing, past the coil and into the carburettor. The air is drawn from a source that will heat up as the engine does – often by taking air from the air filter and passing it over the exhaust manifold before feeding to the choke housing. As the vehicle warms up, the hotter air heats the coiled spring. The spring expand, moving the choke rod to open the choke plate. It can be a challenge to find a source of hot air in aftermarket manifolds. One solution is to draw air from a clean source (preferably inside the air filter) via a

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thin ductile copper tube. The copper tube is wrapped a few times around the exhaust manifold (or an extractor pipe) before being connected to the choke housing. The choke housing thread is a weird one, though a 12.7x0.91 annealed copper tube (from Bunnings) fits over it with a little persuasion..

11.3.4 Automatic Choke Tuning The following tuning points are available for Holley automatic chokes: a) Adjusting how much the choke plate pulls open when the engine first fires. As a starting point, the factory tuning settings can be used. The integral chokes which are bolted onto 350 Holley carburettors are normally of two types – either with an adjusting screw, or without one. If the adjustment screw is present on the side of the choke housing, the following can be used as a starting point:  Dig the caulking out of the adjustment screw with a sharp pick.  Remove the choke cap and push the choke pull-off piston inwards (onto the adjustment screw shoulder).  Apply light closing pressure to the choke plate, then use drill bits to measure the gap between the top edge of the choke plate and the air horn wall (put the drill bit in parallel to and adjacent to the air horn vent, but up against the carburettor wall).  Adjust the screw in or out to give a gap of approximately ¼”. Turning the adjuster screw counter-clockwise (out) will open the gap, turning the adjuster screw clockwise (in) will close the gap. Note that the adjustment screw should be sealed over again once tuning is finished to prevent vacuum leaks. If the adjustment screw is not present on the side of the choke housing, the following can be used as a starting point:  Bend a paper clip so that it has 1 an /8” end.  Remove the choke cap and insert the paper clip into the end of the choke pull-off piston. Feeling gently, hook the paper clip into the piston bore slot.  Move the piston in until the edge of the piston slot engages the paper clip. The piston is now “pinned” into the bore by the paper clip.  Apply light closing pressure to the choke plate, then use drill bits to measure the gap between the top edge of the choke plate and the air horn wall (put the drill bit in parallel to and adjacent to the air horn vent, but up against the carburettor wall).

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b)

c)

 Bend the piston lever tang to give a gap of approximately ¼”. Once this basic setting has been made (and the choke cap reassembled), start the vehicle and observe how the vehicle performs for the first thirty to sixty seconds:  If the choke plate refuses to move at all when the engine first fires, there may be a number of reasons: o the cork seal is installed in between the main body and housing may be missing, o the hot air supply may be blocked with carbon, or a lead ball, o the linkages or the piston could be binding, or o the vehicle may have a very, very lumpy cam and make insufficient vacuum to move the pull-off piston.  If the engine is running overly rich (black smoke, strong smell of unburnt fuel, or rich-stalls), adjust the choke pull-off to open the choke plate a tiny bit more.  If the engine hesitates, backfires or lean-stalls, adjust the choke pull-off to close the choke blade a tiny bit more Be careful, as a tiny change in the choke pull-off is amplified by the linkage and makes a big difference to the choke plate position. Adjusting how long it takes the choke to start opening once the engine has fired. The choke plate should be tightly shut when the engine is cold. With either of the hot-air or electric chokes, start the choke coil adjustment by turning the mark on the choke coil to the index position on the housing. To adjust the choke coil, start the vehicle and let it run for thirty to sixty seconds.  If the engine hesitates, backfires or stalls after the thirty to sixty seconds, the choke is probably opening too soon. Loosen the three lock screws (see red arrows in the image above) and turn the choke cap one index mark anticlockwise (RICHER). Tighten the three lock screws, let the engine cool all the way down then repeat the tuning.  If the engine is running very rich (black smoke or the smell of unburnt fuel) after the thirty to sixty seconds, the choke is probably opening too late. Loosen the three lock screws and turn the choke cap one index mark clockwise (LEANER). Tighten the three lock screws, let the engine cool all the way down then repeat the tuning.  If the choke plate won’t open all the way even long after the engine has warmed up, the problem issue is almost certainly a lack of heat to the choke coil - blocked exhaust crossovers, missing or defective heat riser valves, blown electrical fuses or blown electric coil. Adjusting the unloader tang. When the engine is cold and the choke is closed, check that the fast idle cam is on the highest step. Push the accelerator slowly to the floor. The choke plate should be observed to be mechanically forced open at least as much as the choke pull-off would open it 11 (about /32”). Although not critical, the amount that the choke is forced open can be adjusted by bending the unloader tang. The tang is pretty heavy, and buried under all the fast-idle linkages – it is easier to remove the choke housing first before bending the unloader tang. The image to the right shows the fast idle screw (item 1) and the unloading tang (item 2). Bending the unloader tang in the direction of the green arrow will crack open the choke plate more.

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11.4 Power Valve Blowout Preventer (Check Ball). It is possible to damage the power valve diaphragm by engine backfire. For carburettor built after 1992, a power valve blow-out protection system (a ball check valve is located in the throttle body, designed to be normally open but which quickly seats to close off the internal vacuum passage when a backfire occurs) is installed. Once closed, the check valve interrupts the pressure wave caused by the backfire, thus protecting the power valve diaphragm. A kit (part number 125-500) is available to retrofit the power valve blow-out protection system to pre1992 350 Holleys. The kit contains a drill bit with stop collar, two check balls, springs and retainers and is installed with the carburettor removed from the vehicle and the throttle plate removed from the main body. Note that two balls/stops/retainers are supplied as the kit is also used on four-barrel carburettors with secondary power valves. To install the kit: 1. Clamp the throttle body gently in a drill press, using soft faces to protect the aluminum. 2. Check that the stop collar is mounted 0.300” from the supplied drill tip and is tight. 3. Locate the power valve passage on the top face of the throttle body (circled in red in the image to the right). Drill the passage larger, until the stop collar contacts the throttle body. 4. Remove the throttle body from the drill press and blow out all passages with compressed air to remove any drill chips. 5. Install the spring (tapered side facing up) into the newly drilled power valve passage, followed by the check ball. 6. Tap the spring retainer into place, flush with the surface of the throttle body.

11.5 Better Fuel Metering (Adjustable Metering Block) An adjustable metering block is available for 350 Holley carburettors (Holley part number 134-276), identified by the numbers "12323" stamped into the casting on its throttle lever side. The metering block is supplied with all Keith Dorton Signature Series 350CFM carburettors, and is used to tune the fuel curve to individual vehicles. Gains of 5-7HP have been reported when the block is used instead of the factory metering block. The adjustable metering block has the following features:  The factory 350 Holley metering block doesn't have emulsion tube holes drilled in to the main well. Common practice is to drill different sized holes in the main well chanels to get the engine to operate at around 12.5:1 air/fuel ratio throughout its power curve. The holes introduce air in different volume amounts (controlled by the number of bleed holes and their diameter), and at different points in the fuel curve (controlled by their vertical placement in the channel). However, once the holes are drilled, they cannot be readily “undrilled”. The adjustable metering block has five screw-in emulsion air bleeds for the main circuit. These are supplied as 0.031”, 0.031”, 0.031”, 0.020” and 0.020” (bottom to top).

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 Similarly, the factory 350 Holley metering block power valve restriction channels (PVCRs) are not adjustable. Common practice is to drill out the PVCRs larger than the factory size (~0.056”). Again, once the PVCRs are drilled, they are difficult to “undrill”. The adjustable metering block has screw-in PVCRs, supplied at 0.042”.  At wide-open throttle (WOT), the high vacuum generated in t he venturis can suck unmetered fuel from the accelerator pump discharge nozzles. The adjustable metering block has an anti-siphon air bleed fitted in the accelerator pump passage just above the main metering jets (sometimes referred to as a “kill bleed”). The bleed is supplied with a 0.020” screw-in restriction. Air introduced into the pump passage by the bleed breaks the vacuum being pulled on the fuel, and stops the accelerator pump feeding the mixture at WOT.  A wide range of screw-on restrictions are available to tune the emulsion air bleeds, PVCRs and kill bleed as per the table below: Part Number 142-00 142-20 142-21 142-22 142-24 142-25 142-26 142-28

Hole Size Blank 0.020” 0.021” 0.0225” 0.024” 0.025” 0.026” 0.028”

Part Number 142-29 142-31 142-32 142-33 142-35 142-36 142-37 142-38

Hole Size 0.0292” 0.031” 0.032” 0.033” 0.035” 0.036” 0.037” 0.038”

Part Number 142-39 142-40 142-41 142-42 142-43 142-46 142-52 142-55

Hole Size 0.039” 0.040” 0.041” 0.042” 0.043” 0.0465” 0.052” 0.055”

Part Number 142-59 142-62 142-64 142-67 142-70 142-73 142-76 142-78

Hole Size 0.0595” 0.0625” 0.0635” 0.067” 0.070” 0.073” 0.076” 0.078”

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12 Contacts

Holley Dealers:

Email: Internet:

http://www.holley.com/dealers/InternationalHolleyDeal erLocator.asp http://www.holley.com/TechService/TechRequest.asp www.holley.com

AussieSpeed Performance Products Address: PO Box 4009 Seaton, SA 5023 Australia Telephone: (04) 03221105 Internet: www.aussiespeed.com Redline Performance (Hardiman Auto Supplies) Address: 9 Bullecourt Avenue Milperra, NSW 2214 Australia Telephone: (02) 87238888 Facsimile: (02) 97712176 Email: [email protected] Internet: www.redlineauto.com.au K&N Dealers: Email: Internet:

http://www.knfilters.com/search/dealersearch.aspx [email protected] http://www.knfilters.com.au

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