I converted a 28cc Ryobi a year ago and have been flying a 1/4 scale cub with it. As this left me with no string trimmer, I picked up another new one on sale. It never ran worth ____. Almost impossible to start, and when it did run, it would not rev up at all.

The problem turned out to be that the ignition timing was way off. When I compared the sick motor to the one I was flying, I could see that the timing was off (retarded) by at least 30 degrees in the sick engine. I filed off the cast in key and tightened the flywheel on the taper at the same position as the healthy motor. The motor starts fine now and revs up normally. I never determined if it was the cast key or the machined slot in the crankshaft that was off.

Just something else to watch out for!