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  1. #1

    Post low speed carb setting for 68 9.5 johnson

    I just performed major tune up coils, points, condensors, wires, and rebuilt fuel pump. The motor will now only start and run at higher throttles and will not idle. Is it possible that the carb mixture and low speed adjustment screws need adjusting due to the tuneup? If so how do you adjust them.

  2. #2
    Honorary Moderator Emeritus tashasdaddy's Avatar
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    Default Re: low speed carb setting for 68 9.5 johnson

    yes, and also could have a dirty carb.

    (Carburetor Adjustment - Single S/S Adjustable Needle Valve)
    (J. Reeves)

    Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

    Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

    Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

    Note: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

    When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway
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