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Thread: 850 CFM 4150 style carb floods under hard braking.

  1. #1

    Default 850 CFM 4150 style carb floods under hard braking.

    I have a '66 Chevelle with a Merlin 509, HEI, dynoed at 570 HP at the crank, 9-10 inches of vacuum at idle, 5 inches in drive, the cam is an Isky roller 300 duration, 608" lift at .020 intake, 617" lift at .020 exhaust, dual-plane manifold. The car runs incredible, except when braking.

    What I have done:
    Float Levels - really low, especially in the back, hardly any dripping out of the sight hole.
    Floats are new - they are not saturated with fuel.
    Added Truck Avenger vents - essentially connecting the front and rear vent.
    Retested, still flooding I have to hold my foot to the floor to start it. Thanks.

  2. #2
    Join Date
    Nov 2014
    Ont. Canada


    Lower the rear float some more.

  3. #3


    Be 100% sure there is no dirt/crud in the needle & seat assembly on both front & rear bowls. I had the exact same problem with 4150 750 cfm, and there was a very small piece of dirt on the tip of the needle not allowing it to seat all the way.

    Quick way to tell if this is happening, is to drive the car and as soon as it starts acting up, pull over, raise the hood and check out the fuel levels in the bowls through the site glass. If the needle & seat aren't closing properly, the bowl will be almost full of gas.
    Last edited by 69cam; 01-22-2018 at 10:36 AM.

  4. #4


    Thanks for the advice, I'll give it a try.

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