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    What makes an 8 Stack Injection spit back through the stacks at idle?

    When you experience “Spit back”  through the butterflies and sometimes spitting through the air vents in the nozzles –  Here are some things to check.

    Barrel valve is set too lean
    Butterflies may be bent
    Bad Valve Job on the heads
    Intake valve adjusted too tight
    Vacuum  Leak around manifold or shafts
    Timing too retarded – Generally timing should be 30-36 Degrees for unblown, injected engines except flatheads  – less for them
    You may be trying to idle it too slow – 1200-1600 RPM is where it will want to idle
    Butterfly gap for 8 Stacks:

    The larger the engine, the more generous you can set the leakdown % since it will want more fuel at idle

    .002” Methanol Leakdown % 16-25

    .003” E-85 Leakdown % 12-16

    .004” Gasoline Leakdown % 8-12