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Thread: Another Stumble Problem

  1. #1

    Default Another Stumble Problem

    Have a stock 1967 Mustang with a automatic transmission and recently rebuilt 289 four barrel. Had a Motorcraft 4300, but was not satisfied with idle and top end power. The carburetor had great bottom end power with no stumble at all. Bought a new Holley 4160 and it runs great, but stumbles every time you give it throttle. It'll die about 30% of the time. If it makes it through the stumble the engine has power like I've not seen before. I've been working on it for a while and can't figure it out and no shops around my area to help. Here the stats and what I have tried:
    1967 Mustang stock 289 2BBL automatic.
    Timing 10 BTDC. Vacuum 18 inHg at 750 RPM. Vacuum 15 at idle in drive.
    *Note. There was no stumble with the Motorcraft.
    *Note does not stumble in neutral. Only under load. Also NO backfire.
    What's been tried:
    Adjusted timing from 4° to 14° TDC.
    Vacuum advance is working properly. It's a Pertronix distributor which worked great with the Motorcraft carb.
    Accelerator pump is adjusted properly.
    Tried orange and white cam.
    Tried nozzels 35, 31, 28, 25. When I tried the 25, I got a little hesitation in park as while as in drive.
    Power valve is 6.5 and new.
    Running 66 jets.
    Wired secondary shut for test and stumble still there.
    Checked everywhere for vacuum leaks. No leaks.
    Mechanical fuel pump pressure 4.75 at idle and increase to 5.9 with RPM. Fuel level at bottom of sight hole.
    Put the Motorcraft back on and there is no stumble at all.
    Conclusion: Must be in the setup of the carb. HELP.

  2. #2
    Join Date
    Jan 2010
    Brisbane, Australia


    Hello there. Your 4160 is the model, what's the list number stamped on the front tower? Gary
    Regards, Gary

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