An additional note I'll add. My engine has a steel piston, pretty heavy because it's nearly solid. It has two rings.
After the engine runs a few hours ( I take it to shows and I'll start it and it will run nearly all day), it seems to acquire a carbon build-up near the bottom of the cylinder. The piston will settle on the top of this ring and will not sink to the bottom of the cylinder so the cycle can repeat.
If I open the exhaust, letting the piston settle faster, it will sink through this build-up, but then it runs too fast with the result that the pawl/ratchet starts to stutter.
Time to dis assemble and clean.