I had a ’55 15 Evinrude that I had some weird coil rubbing issues with. It turned out to be that the crank bearings and bushings were worn out. When I rocked the flywheel side to side, left to right, fore and aft, it moved a bit more than “normal,” and you could hear an ever-so-slight, “tic-tock.” For what ever reason, it seemed to be worse when it had run for a few minutes, like yours. Maybe your upper and/or lower bushing is worn out? It might also explain what seems like some difficulty in keeping it tuned?
Long live American manufacturing!
