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Thread: Secondary carbs

  1. #1
    Join Date
    Aug 2014
    Location
    Holley, New York
    Posts
    13

    Default Secondary carbs

    I am having a problem with the rear carb with excess fuel running into the bores. I originally thought it was a problem with the float, but that looks really good with no leaks. I submerged it for several minutes in water, about 20, when I released it, it came right back up to the surface, and no water was inside when I shook it.

    Next I checked for pump discharge leakage. There was a small gasket between the venturi cluster and difuser, (synchromesh), but no gasket between that and the screw head. So I placed a gasket there.

    That only leaves the needle and seat.

    This had been a problem up until 3 years ago when I pulled the entire intake set-up off and ran the Carter AFB. 2 years ago I rebuilt the carbs and checked everything out with a fine tooth comb. So it has been sitting on the bench for the last couple years until a month ago when I decided it was time to reinstall it. When I put fuel to the carb it looked like a faucet running.

    Even though the needle and seat and gaskets were new. Is this just from sitting and need a new needle and seat, or is there a bigger underlying problem that I am not picking up on? Thank you for any help. Scott

  2. Default

    I assume you are setting the correct float level. If you are not a racer drop the float level a 1/16". Also does the engine have to be running or will they leak when cranking it over? Do they keep leaking with the engine off? Have you checked the fuel pressure? If they leak only when the engine is hot the gas may be boiling off. Does your fuel system have a return line to the tank? If it is only a hot problem try adding insulators under the carbs and insulating the fuel line from the pump to the carb.

  3. #3
    Join Date
    Aug 2014
    Location
    Holley, New York
    Posts
    13

    Default

    Thanks BobW. Not a racer. Fuel will start overflowing as soon as I start the car, then will continue to run after the car is shut off, till the fuel gets to a certain point. It is a stock '66 setup, with no return lines. I have the float set per '66 shop manual, float level at 21/32" and the float drop to 1-3/4". I have the front carb set the same with no issues. I have ordered a new Daytona Float Valve set-up (needle and seat assembly) from Daytona Parts. The only other thing I can think of is possibly a crack in the airhorn that I can't see in the needle seat area. Also running an AC-Delco fuel pump purchased from Ames Performance back in the 90's. I don't believe this to be the issue as it has run with the Carter AFB with no problems.

    When I first installed the tripower a couple months ago, i ran the center carb only with block off plates over the secondaries, with a mocked up fuel line only to feed the center carb. Dialed the center carb in all by itself, and got it running really good. I ran it like that until a month ago when I added the secondary carbs. The rear carb started leaking right from the get-go.

  4. Default

    If you had a leaky float there would be gas in it and you would feel it. I doubt you have a crack in the carb. It probably is a bad needle and seat. Years ago a friend of my family invented a substitute for the needle and seat and they were available locally and mail order. They used 2 ball bearings of different sizes to stop the flow of gas. The gentleman passed away so they are not available anymore. They worked so well I wish I had bought a bunch of them then. Good luck.

  5. #5
    Join Date
    Aug 2014
    Location
    Holley, New York
    Posts
    13

    Default

    I got the Daytona Float valve installed and with my short test drive it seemed to fix the problem. The venturi area was dry and no more signs of leaking fuel. Thanks for the help!

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