Re: 1958 35hp OMC drops one cylinder at low throttle

[jerry-ahrens]

Agreed, I think the problem is in the ignition system. Did you replace the spark plug wires back when the coils were replaced? The reason I ask is this, some of the auto parts 7 mm plug wire is poorly made, and will chafe after the motor is used awhile. This is caused by the wire rubbing back and forth with the movement of the mag plate. At certain throttle positions, it can cause a cylinder to arc to ground, where the wire is damaged, then correct it’s self after the throttle is advanced. Problem is, they don’t make most spark plug wire as well as the original 50’s stuff. I would take a look at the wires too see if this could be the problem. In short, time to pull the flywheel and have a look. If you are using Sierra ignition points, they are notorious for these kind of problems. I would also check for a worn mag plate bushing…. this will cause the mag plate to be sloppy and move around at idle speed. Keeping a good point gap will be impossible.