I guess I would start with a basic spark test with the throttle at known good running and problematic positions. That system should jump a 3/8″ open gap, all day long. If you find a discrepancy, swap the coils and see if the problem follows. Don’t forget a compression test, too, just to be sure both cylinders are bringing the same thing to the proverbial table. Then there are the surface gap plugs. Very prone to low speed fouling. There IS a conventional gap type for that engine, too; but I don’t recall the number. Then I would start thinking about going deep…a lower seal or reed not closing all the way. Let’s hope for a spark problem.
Long live American manufacturing!
