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Thread: 4150 High Idle

  1. #1
    PMJJ Guest

    Default 4150 High Idle

    I have a 4150 double pumper, mechanical secondaries, 4 corner idle screws. Carb had a mechanical choke but I just milled off the choke housing, and took the linkage off the carb. Question is: the carb will not drop the idle down below 1500 or so. Curb idle screw is backed out all the way, the intake has been triple checked for leaks, carb base gasket for leaks, no vacuum leak anywhere. mixture screws are about 2 turns out. The timing is set correctly. I just disassembled the carb completely for the milling and cleaned it all. The carb did this before I machined it as well. Any thoughts would be appreciated. Thanks a lot, Pete.

  2. #2


    Have you checked the secondary idle screw? You can only get to it with the carb off & upside down. With the carb off can you see daylight through any the venturis? If so then the throttle plates are not closing all the way. Z.

    '66 GT-350 Original Drivetrain, Sheet-Metal, Interior, & Paint

  3. #3
    kd5icr Guest


    I would like to know what the spark plugs look like. Milling the choke horn off you could have cracked the body causing an internal fuel leak that you wont see.

  4. #4
    PMJJ Guest


    I found the problem. Good old intake leak, even though I said I double checked the entire intake. Intake gasket on the LH side pushed up in two spots. Problem was I couldn't see the carbon stain due to a 3/4" round wire loom running right down that side. Found the leak with some brake clean while she was running. Rolled the wire loom over and sure enough it was black on the bottom! Thanks for the inputs. Pete.

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