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Thread: Holley Vacuum Carb Question

  1. #1
    Join Date
    Jan 2007

    Holley Vacuum Carb Question

    We have a 74 Camaro with a 383, 12.5/1 compression, solid roller cam, Vic JR intake with a vacuum holley carb.

    The carb was used when I got it but nearly new. However, I have never thought it was working right.

    What I noticed today, at about 1000 rpm idle, I can lift the secondary plate open a little and when I do, the motor dies dead. With engine off, I can lift the secondary open a little without opening the primary all the way etc.

    My quesiton is, if I open the secondary with the engine running, should it die like that? I set the idle up to about 1500 rpm and it did the same thing. There appears to be no gas going in the secondary. The bowl is full however when you look in the inspection port.

    Should it be doing this?

  2. #2
    Senior Member RACING JUNKIE
    Join Date
    May 2006
    I first off would recommend a double pumper for your application.

    It sounds like you got an all out race motor on your hands and well I vacuum secoundary carb just aint gonna give you the performance you'd get out of an double pumper.

    Back to your problem.

    The secoundaries on a vacuum carb don't have jets like the primaries do, it has a metering plate, its a weird set-up to say the least and I'm not really "UP" on them but it sounds like you might have some blockage in the metering plate itself, remove the bowl and you'll see the meter plate on the back of the carb center section, remove the even weirder metering plate bolts and clean the plate out real good with some carb clean and compressed air, remember to blow out the feed holes in the carb center section as well.

    Goodluck, Cp
    ***IN GOD WE TRUST***

  3. #3
    Senior Member RACING JUNKIE oldandtired's Avatar
    Join Date
    Dec 2008
    Sugar Hill, GA
    The reason your engine quits, is a severe case of lean. A vacuum secondary is only metering fuel (remember no acc pump) to the intake when the engine is putting a lot of vacuum thru the side pod. In fact, many vacuum secondary carbs never open all the way!!
    Get one of the Holley quick change housing kit and the spring assortment (# 20-59 and 20-13, less than $30 total). Start with the lightest spring and work your way heaver. You will be able to tell when the engine likes it !!

    A rebuild would be insurance and also make sure you have selected the correct power valve.

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