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Thread: 4150 gone bad?

  1. #1

    Default 4150 gone bad?

    Hey gents. I have a mid '90s produced 4150 (primary only idle circuit). I had a fuel tank rust out last year, and clogged up the carb. I found sediment in fuel bowl, but didn't know what it was. I refreshed the carb not knowing I had a rusted tank, ran good for a couple days, then went bad, I figured it out that I had rust in the tank after the fact, thought it clogged it back up, but maybe not. I have since replaced tank, sending unit, filter, pump (Edelbrock 110 GPH, 6 psi pump), flushed hard line, replaced all rubber hose, refreshed carb, have dipped in chem-dip several times, and dipped in Evapo-Rust.(which produced a lot of trash). The car will not idle on idle circuit, runs out of gas immediately. Disassembled, cleaned more, no change. Recently purchased a QFT 34-4 billet metering block, still won't idle. Sight plug out, fuel level stays right. I have a long duration cam that typically makes about 10.5-11 inHg vacuum at 800 RPM idle. Runs good on manual choke until warm up with old and new metering block. Check main body for throttle plate gasket surface variance and got no more than .007", which the gasket should easily compensate for. I noticed last night, may be a new development, that a good bit of fuel leaks out of both primary and secondary annular boosters after shut off (even with sight plug removed, so it's not due to pressure, I assume) and of course floods the engine within a few minutes. Never did that before that I recall. I can get an 1,100 RPM idle off idle circuit by turning stop screw in, but even then it will slowly start to run too lean to run and sputter and die. Mixture screws have always liked 1 and 3/4 turns on this engine and they are currently out 2.5 turns after trying 1.5 initial. I know it's lean because I've had this combination for 17 years and I can smell when it's right. Have tried an old Demon carb from a friend and it idles fine. I can not make sense of fuel leaking after shut off. It's almost like the metering blocks build pressure. Time for a new carb? Gamble on a replacement main body? Please help!
    Last edited by 1776 Woody; 07-11-2020 at 07:57 AM.

  2. #2
    Join Date
    Jan 2010
    Brisbane, Australia


    Did you blow the idle circuit passages clear in the throttle body when you cleaned the carb up? A different metering block still has the same fault, so either the idle passages are blocked after the mixture screw in the main body, or the throttle body. Gary
    Regards, Gary

  3. #3


    I'm fairly certain I've blown them out thoroughly. The throttle plate passage is easy to see, main body, not so much. I suppose I could disassemble once again and go through main body passages one more time. I did use a small LED light designed for looking into a rifle bore and light passes through the main body passage ways. I'd think fuel would also. Thank you for the reply.

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