Assuming its a 2 cyl?
maybe swap coils?
I had a bad coil that was internitantly firing on then spark plug and under the coil to the engine.
Just a thought.
i was installing all new guts, and just didn't get the plug wire totally connected. got it started, and running, but at lot of adjusting to do. also have to drop foot,again, as new impeller is not pumping.