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Discussion Starter #1
I keep on seeing people say i have a double pump vac secondary do those exist i thought that double pumpers were what they called mechanical secondary carbs. I just wnated to know if double pump is how holley calls there 4 barrel or if its just a mistake?? thankx
 

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A double pumper is one thing and a carb with vacuum secondaries is another. Double pumper refers to a carb which has accelerator pumps and power valves for both the secondaries and the primaries. Carbs with vacuum secondaries aren't typically double pumpers. More typically, mechanical secondaries and double pumper set ups go together.

Not to say you COULDN'T have a double pumper with vacuum secondaries, it just wouldn't be all that effective or work that well. Double pumper Holleys usually have dual fuel inlets as well.
 

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Gumball
a double pumper is a holley with 2 excellerator pumps,one primary,one secondary.the secondary throttle plates on a double pumper are mechanically operated.along with the exell pump.
a vacumm secondary carb has a vacumm canister that opens the throttle plates at a set vacumm,a spring in the canister sets when and how fast the secondarys open.most vacumm secondary carbs are single fuel feed,some are dual feed.while double pumpers are mostly daul feed,I have had a spread bore holley that was single fuel feed,double pump.hope this helps---67RAT member #199
 

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I think that mechanical secondaries need their own accelerator pump because since the secondaries can open instantly, a lean condition would exist if you waited for the fuel to be sucked in the normal way. I haven't personally checked it, but I would assume that without it, you would get a dead spot or boog when you stomp the pedal.

Vacuum secondaries open slow enough to where it is not an issue.
 

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Discussion Starter #5
Thank you for the responses i just kept seeing people say double pump vac 750 holley and i was pretty sure that just meant vac but now i do see why they call them dp's thankx again guys
 
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