Are you working on some of these engines for others? I was just wondering because you've had a lot of problems at the same time on different units. It's not a problem and I like trying to figure out engine problems. I am curious.
Doe's this engine run fine below full throttle and at idle. If it doe's then like mentioned above you probably have a high needle out of adjustment. Sounds like a lean missfire. Try going counter clockwise half a turn at a time. Sometimes the main jet gets clogged and you'll need to blow that out.