Paul's Daimler Diary, balancing the Strombergs.

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Stromberg Page 2 - Go to page one two three four five 2. Before You Even Touch the Carb's! Start with the engine warmed up to operating temperature and perform your standard ignition tune-up (points gap, timing, spark plug gap, new condenser, etc.) first. All of these things can affect the setting of the carb's, which should be adjusted last, if at all! After being properly set, the carb's should rarely need further adjustment. If you've got a timing light and a dwell meter, you can verify the ignition components independent of the way the car is running. When it's warm, shut the motor off and remove the air filters. Of course, it helps if the carb's are in good mechanical condition as well. But you can consider a rebuild once you have gotten things working first! 3. Balancing The Air Flow But first a note from Roger Bywater of AJ6 Engineering (Roger worked for Jaguar on the development of the V12 engine and now owns a tuning firm specialising in the V12 and other Jag engines - Paul.) “…. the manometer idea is equally unsuitable as a means of balancing multiple carburettors. Indeed it is probably even worse than the old and discredited idea of trying to equalize the hissing noises of the carbs by listening to them with a length of pipe. Yes, I know that method is mentioned in various Jaguar workshop manuals, but those were just throwbacks to the days when they didn’t know any better. By the 1970s any raw fitter trying to do it that way in the Emissions Department at Jaguar soon had the folly of it demonstrated to him with the aid of a simple flow meter. Crypton used to sell a useful little airflow meter called a ‘Synchro-check’ which is quite handy for quickly checking carbs on the car but I always found that the same equalisation method as for an EFI system worked as well as any, particularly with four carb V12s. It is just a matter of carefully assembling all the carbs on the bench top with float heights, etc., all exactly the same (actually if they are not all set exactly the same no method of balancing is likely to work) and the butterflies centred, set to 0.002'' clearance, then opened by exactly 2 turns on the screw for a basic idling condition. Obviously all the mixture trimming ancillaries attached to the carbs must be in proper working order. Any subsequent adjustments are then applied exactly equally to each carb until the required idle speed and exhaust CO figures are obtained. Of course the throttle linkage must be so adjusted that the movement of all carbs is synchronised. Whatever tolerance differences there might be between carbs is always likely to be less significant than tolerance differences between individual cylinders.” ... End. Paul's thoughts on balancing the air flow Roger is the Guru on V12s. I would go with the method he recommends. It's the modern professional's way of synchronising the butterfly throttles after sorting them on the bench. However, if the engine is running very rough and the carbs are staying on the car, then balancing with an air flow meter is a relatively quick way of improving things. If your carb's are already off the car, then do it Roger's way. I used a Gunsons "Carbalancer" - a slightly poor quality air flow meter - but better than the hosepipe in the ear method. You'll have a merry dance round the front of the car trying to balance each bank! After you do one side, you'll find that it needs doing again when you've matched the opposite bank, and so on and so on. It can take several attempts to get all four synchronised. This is another reason why I recommend Roger Bywater's method. Now back to the original article....... If your car has multiple carburettors, the air flow needs to be balanced amongst all carb's before the mixture is adjusted. If you have only one carb on your car, you can proceed directly to mixture adjustment! 1. Begin by balancing the air flow. To do this, first loosen the throttle linkage nuts. Leave them connected, just loosen them half a turn or so. 2. Back out the throttle stop screws till you can see that they are just touching the throttle stop. Then open each carburetor (that is, lower the throttle stop screw) 1-1/2 turns of the throttle stop screw and start the engine. It will probably idle at about 2000 RPM; don't worry. 3. Put the Unisyn over either carb and adjust the orifice in the Unisyn till the little float at the side rests at the middle of its graduated tube. (Pre-diagnostics: if the idle drops and the car wants to die when you slap on the Unisyn, the carb is too rich; if the idle soars upwards, it's too lean.) Hold the Unisyn over the carb for only long enough to see the level of the float, then remove it. 4. Place the Unisyn on each carburettor in turn to check its flow, adjusting the throttle stop screws until all carburetors register the same position on the graduated tube of the Unisyn. (The float will probably move either up or down in the tube, which is why you want to centre it in Step 3.) When both carburettors flow the same amount of air, tighten the throttle linkage nuts, adjusting for the amount of free-play between the linkage and the throttle stops that your manual calls for (probably about 0.006"). Your goal should be to achieve the lowest possible idle with both carb's balanced and the engine running smoothly. (Note that the idle speed will very probably rise as you get the mixture correct.) If you've taken more than five minutes to do this, rev the engine to over 2500 RPM (assuming the idle isn't already that high) for thirty seconds or so to clear the spark plugs. Then adjust the mixture. Stromberg Page 2 - Go to page one two three four five This site is for the benefit of enthusiasts. Much of the content is my own to use as you wish. However, some I have collected from various (forgotten) sources in the public domain. If you are the owner of any material used and wish it to be removed or so accredited, please contact me. Web Site © Double Six Design

Stromberg Page 2 - Go to page one two three four five

2. Before You Even Touch the Carb's!

Start with the engine warmed up to operating temperature and perform your standard ignition tune-up (points gap, timing, spark plug gap, new condenser, etc.) first. All of these things can affect the setting of the carb's, which should be adjusted last, if at all! After being properly set, the carb's should rarely need further adjustment. If you've got a timing light and a dwell meter, you can verify the ignition components independent of the way the car is running. When it's warm, shut the motor off and remove the air filters.

Of course, it helps if the carb's are in good mechanical condition as well. But you can consider a rebuild once you have gotten things working first!

3. Balancing The Air Flow

But first a note from Roger Bywater of AJ6 Engineering

(Roger worked for Jaguar on the development of the V12 engine and now owns a tuning firm specialising in the V12 and other Jag engines - Paul.)

“…. the manometer idea is equally unsuitable as a means of balancing multiple carburettors. Indeed it is probably even worse than the old and discredited idea of trying to equalize the hissing noises of the carbs by listening to them with a length of pipe. Yes, I know that method is mentioned in various Jaguar workshop manuals, but those were just throwbacks to the days when they didn’t know any better. By the 1970s any raw fitter trying to do it that way in the Emissions Department at Jaguar soon had the folly of it demonstrated to him with the aid of a simple flow meter.

Crypton used to sell a useful little airflow meter called a ‘Synchro-check’ which is quite handy for quickly checking carbs on the car but I always found that the same equalisation method as for an EFI system worked as well as any, particularly with four carb V12s. It is just a matter of carefully assembling all the carbs on the bench top with float heights, etc., all exactly the same (actually if they are not all set exactly the same no method of balancing is likely to work) and the butterflies centred, set to 0.002'' clearance, then opened by exactly 2 turns on the screw for a basic idling condition.

Obviously all the mixture trimming ancillaries attached to the carbs must be in proper working order. Any subsequent adjustments are then applied exactly equally to each carb until the required idle speed and exhaust CO figures are obtained. Of course the throttle linkage must be so adjusted that the movement of all carbs is synchronised. Whatever tolerance differences there might be between carbs is always likely to be less significant than tolerance differences between individual cylinders.” ... End.

Paul's thoughts on balancing the air flow

Roger is the Guru on V12s. I would go with the method he recommends. It's the modern professional's way of synchronising the butterfly throttles after sorting them on the bench. However, if the engine is running very rough and the carbs are staying on the car, then balancing with an air flow meter is a relatively quick way of improving things. If your carb's are already off the car, then do it Roger's way.

I used a Gunsons "Carbalancer" - a slightly poor quality air flow meter - but better than the hosepipe in the ear method. You'll have a merry dance round the front of the car trying to balance each bank! After you do one side, you'll find that it needs doing again when you've matched the opposite bank, and so on and so on. It can take several attempts to get all four synchronised. This is another reason why I recommend Roger Bywater's method.

Now back to the original article.......

If your car has multiple carburettors, the air flow needs to be balanced amongst all carb's before the mixture is adjusted. If you have only one carb on your car, you can proceed directly to mixture adjustment!

1. Begin by balancing the air flow. To do this, first loosen the throttle linkage nuts. Leave them connected, just loosen them half a turn or so.

2. Back out the throttle stop screws till you can see that they are just touching the throttle stop. Then open each carburetor (that is, lower the throttle stop screw) 1-1/2 turns of the throttle stop screw and start the engine. It will probably idle at about 2000 RPM; don't worry.

3. Put the Unisyn over either carb and adjust the orifice in the Unisyn till the little float at the side rests at the middle of its graduated tube. (Pre-diagnostics: if the idle drops and the car wants to die when you slap on the Unisyn, the carb is too rich; if the idle soars upwards, it's too lean.) Hold the Unisyn over the carb for only long enough to see the level of the float, then remove it.

4. Place the Unisyn on each carburettor in turn to check its flow, adjusting the throttle stop screws until all carburetors register the same position on the graduated tube of the Unisyn. (The float will probably move either up or down in the tube, which is why you want to centre it in Step 3.)

When both carburettors flow the same amount of air, tighten the throttle linkage nuts, adjusting for the amount of free-play between the linkage and the throttle stops that your manual calls for (probably about 0.006"). Your goal should be to achieve the lowest possible idle with both carb's balanced and the engine running smoothly. (Note that the idle speed will very probably rise as you get the mixture correct.)

If you've taken more than five minutes to do this, rev the engine to over 2500 RPM (assuming the idle isn't already that high) for thirty seconds or so to clear the spark plugs. Then adjust the mixture.

Stromberg Page 2 - Go to page one two three four five

This site is for the benefit of enthusiasts. Much of the content is my own to use as you wish. However, some I have collected from various (forgotten) sources in the public domain. If you are the owner of any material used and wish it to be removed or so accredited, please contact me.