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Old 10-05-2008, 11:06 AM
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accelerator pump questions

hey just picked up a 850 holley at a swap meet cheap that has 50cc accelator pumps
i have never done to many mods to carbs and was wondering was the benefit was to the larger pumps?

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Old 10-05-2008, 06:20 PM
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The large pumps help to cover a "hole" or "flat spot" that occurs when the throttle is opened.

In the case of the carb you have it was probably the previous owner's effort to get the engine running right with a carb that was way too big.

Normally if there is plenty of engine underneath the carb the 30cc pumps would probably be enough.
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Old 10-06-2008, 07:27 PM
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Hey rustydawg said, a 50CC pump kit purcase can allot of times be a cover up for some other carb/ignition problems and on most carbs a 30CC pump is enough.......But in the case of a 850 Holley, they have the largest venturi and butterfly diameter in the whole family of 4150 style the top of each venturi it measures 1.600 and the butterflys measure 1.750...that leaves hardly no taper in the venturis and the air speed down low is real bad......causing allot of "transfer" style issues.....and a large "hole" of instantly opened up CFM introduced to the engine, hence making it nessesary for the bigger 50CC pumps to help cover up the flat spot.....If your engine is realitivly healthy then you should keep the 50CC pumps on there becasue you will probably need them.......Later, Jesse @ BIGS!!
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