icebird_1981

just wonder what is the diffrence in a holley double pumper and not double pumper >(think its called vacume secondary?)

RB83L69

Manual secondary carbs have an accelerator pump on the secondary throttles, so that when teh driver just stomps it and opens them, there's a shot of fuel there too.

The secondary throttles in vacuum secondary carbs are operated by the venturi vacuum (measurement of flow) in teh primary venturis. In other words, they are clibrated such that they cannot open too soon, by design. They don't need a pump.

icebird_1981

ok so is there a diffrence in performance? what would make u want a double and not a double?

RB83L69

Think of them as being like transmissions.... vacuum is like an auto trans, manual is like a stick; you even use them together that way. Constant fine-tuning by the driver vs. automatic machine control.

A manual sec carb will almost always go faster, but a vacuum one will be more consistent.

Real racers drive man sec carbs.

icebird_1981

thanks, thats a perfect answer, i found out what i wanted to no.