Reply To: 1975 Johnson 15R75C 15 hp

[Don]

These early versions were a hated due to plug fouling issues and that much hated but misunderstood “low tension” ignition system… This system isn’t all that bad once understood.  The key is to make sure the mag plate bushing does not get worn resulting in erratic point gap along with coil magnets hitting the flywheel.

There were several modifications that were supposed to be made to these engines to minimize plug fouling issues, including a new cylinder head.  So, if I had to guess here, I’m thinking one of the plugs fouled and it is running on one cylinder.  Confirm that the new prop is the same pitch as the one it replaced though.