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Thread: Primary Bowl Inlet Fitting Leak

  1. #1
    Bigblox1 Guest

    Default Primary Bowl Inlet Fitting Leak

    I have a stock 1970 vintage Holley 4150 Dual Feed Carb (Sorry, don't have the Air Horn number handy) that I'm using on my stock `68 Chevrolet L72 427 in my `68 SS427 4-speed Impala. I am using all stock (NOS) fuel inlet lines, tees, and fittings, with a stock L72 mechanical fuel pump.

    This carburetor has developed a chronic fuel leak at the Primary Bowl Fuel Inlet Fitting between the Float Bowl Body and the Inlet Fitting gasket. This started out as just a slight amount of noticeable "dampness" around the fitting that I could occasionally smell and feel on my finger tip in that area after several miles of driving. I could generally wipe it down with a rag and it would remain dry after that until the next time it was driven. The leak has become increasingly worse to the point where I can actually watch the fuel "percolate" or bubble out between the Float Bowl Body and the Inlet Fitting Gasket. All other fittings, tees, and fuel lines are completely dry, and the Secondary Float Bowl Inlet Fitting is dry as a bone.

    I have to this point:

    > Replaced the Primary Inlet Fitting, gasket, and Inlet Filter & Spring multiple times using all new components.
    > Replaced the Primary Float Bowl Assy' with an identical NOS replacement using all new Holley internal rebuild parts (gaskets, o-rings, Float, etc..) Nothing unusual noticed internally during that rebuild.
    > Replaced and rebuilt the Primary Accelerator Pump Assy' with all new Holley components.
    > Adjusted everything to Holley recommended specs. (Pump, Fuel/Float level, etc..) Vacuum readings also look good, and are in spec.

    I have also ensured that all torque settings for all of the afore mentioned fittings and hardware are in spec during all this rebuild/replacement process, but the Primary Inlet fuel leak has not been eliminated. I am starting to think there has got to be a source of back-pressure or blockage somewhere internal to the Primary circuit that is great enough to push the fuel in the Float Bowl out past a properly torqued Inlet Fitting and gasket (?) I have broken the fuel line at other locations just to see if there is excessive pressure built up in the line when this leakage is occurring, but there does not appear to be. I'll just get a "normal" trickle of drainage onto a shop rag - no indication of pressure build-up.

    Any input or suggestions you could provide on resolving this issue would be greatly appreciated.



  2. #2
    Join Date
    Nov 2009


    If there was a blockage, fuel would come out the boosters before it would the fitting. You can check the bowl vent to make sure it is clear, but I do not think this is your problem. As for the leak, you have replaced everything that could be faulty, except you did not mention replacing the fuel line going into the primary fitting. It sounds like there could be a hairline crack in the inverted flare causing your leak. Take a look at it and see if it does not help.

    1972 Rally Nova
    1972 C-10 Short Step
    1970 Rally Sport Camaro
    1986 Chevy Silverado K10
    2009 F150 Lariat

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