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Thread: 750 HPVS Tuning Question

  1. #1

    Default 750 HPVS Tuning Question

    I have a 750 HP vacuum secondary carburetor. If I disable the secondaries so itís a two barrel, should I be reading 13-14 AFR at full throttle on just the two barrels? Iím getting around 15 AFR on the two barrels, but Iím getting 13.5 AFR on all four. Iím wondering if I should go up on the PVCR jets from the 71 I have now and down on the secondary main jets. Thanks.

  2. #2
    Join Date
    Jan 2010
    Brisbane, Australia


    You have 13.5 AFR when the carb functions as a 4 barrel.
    The primary side is set to slightly lean side (15:1 AFR) to help with fuel economy.
    The secondary side is slightly richer to even it up (12:1 AFR) to give you 13.5 AFR.
    You could square it up a bit if you like, but fuel economy might suffer.
    Typically, the primary main and PVCR should be approximately equal in area to the secondary main. Gary

  3. #3


    Thank you. Thatís what I figured, just needed some verification.

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