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Carb sync update problems air leak high air flow rate

1621 Views 2 Replies 0 Participants Last post by  JRV
So I've got the carbed syn

So I've got the carbed sync'd pretty well. I understand the process fairly well, was able to sync each barrell, then each carb between banks, and then each bank.

Everything is flowing, according to my syncrometer (STE SK1), at 7 kg/hr +/- 1/2 kg/hr. I know that this seem high. Idle is fairly smooth and steady at 1000rpm. I've adjusted the idle mixture screws and am fairly confident that each is in the "range" of contributing to highest RPM, although where in that range I don't know (probably need to get a colortune).

So, the symptoms that I know are not good:

** 1. High airflow rate: 7 kg/hr for each barrell

** 2. When I "goose" the throttle, and then release it, the RPMs continue to climb even after I've released the throttle, and are very slow to come back down (Maybe takes five seconds to return to normal)

** 3. When I spray starter fluid at the carb bases (right on the insulator gaskets), the RPMs rise significantly (maybe 500rpm). Each carb appeared to exhibit this behavior.

NO WAY! I just had these rebuilt by Pierce Manifolds. There is NO WAY that I can have an air leak?? They straightened the carbs so that they were true, and every gasket is new in the thing.

For each carb, I used ONE 3mm thick black plastic base gasket piece, with very thin (1/3mm) light brown colored, pattern-printed factory gasket on either side of it. There were four additional regular 2/3mm thick gaskets, part of the rebuild kit which I did not use; they weren't on before and don't show up in the parts manual.

So, either I put them on the intake manifold wrong, over- or under-torqued the carb nuts, didn't use the proper intake manifold <--> carb gaskets, or Pierce Manifolds rebuilt me some leaky carburettors.

Any ideas?
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Try isolating the exact areas

Try isolating the exact areas you are spraying, meaning JUST the gaskets or JUST the throttle shafts etc.....

A cleaner safer way to test is to use a small propane bottle (plumbing type) with a 1/8th dia tube approximately 1 foot long fitted to the bottle. Place the tube right where you want to test.

I hope it's just a matter of under-torquing.

7 seems very high, should be b

7 seems very high, should be between 3.5 & 4.5 on a well tuned engine.

On carbed cars I like to see an idle rpm of no more than 950, recheck timing on both banks to insure it isn't creeping up and that it returns to initial (7 BTDC) quickly. Make sure linkages are not binding or out of adjustment front to rear. After opening throttle & closing gently push on the carb levers to insure they are on the stops and not staying slightly open. You can check for air leaks using soapy water in a spray bottle. the mess. Yes you definately need a colortune (minimum) to check mixture adjustments cylinder to cylnder.

Regards, JRV
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