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Thread: Erratic Vacuum

  1. #1
    bigvette1 Guest

    Default Erratic Vacuum

    I have the SA 770 cfm on a 73-454. Vacuum at idle is 16- to top of 17", but bounces back and forth 1 points. Adjustment of the idle mix screws assists but does not eliminate the bounce.

    The cam is fairly calm, 218/218 @ .050 with .500" lift.
    Timing is rock solid at 12 degrees.
    Crimping one vacuum line at a time makes no change. Spraying carb cleaner around the base gasket makes no difference.

    The reason of some concern is the vacuum used to be in the 18" range .

    Am I chasing a ghost or is there a problem to be addressed. Thx

  2. #2
    Join Date
    Mar 2010
    Bowling Green KY


    It is normal for a vacuum gauge to bounce up and down a point or so on the gauge especially with aftermarket cams. Were you running the same cam when you seen the higher readings? I feel that you probably do not have a vacuum leak if these are the only symptoms you are having I would consider it normal and gauge variation, you may try a liquid filled gauge for a more stable needle.
    Thanks, Travis
    Holley Performance Products
    Technical Service Representative

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