Towards the end of my 2022 summer trip, I had trouble starting my para motor, and on my last flight, the engine briefly went to idle before recovering a few seconds later period I decided to take apart the engine and figure out what was wrong.

As soon as I got the head off, I could tell that there was something wrong. Both the inside of the head and the top of the piston have these odd circular digits in them:

I took the top end off, and I could see that there were these troughs inside of the piston as well:

Continuing the tear-down, I found that a roller bearing had disintegrated, and the rollers had gotten between the top end and the piston wall, which caused the scarring on the side of the piston. They then got up beyond the piston into the combustion chamber, which is why there are round divots in the top of the piston and the inside of the head:

I ordered and replaced the roller bearing, top end, and piston.  The engine runs like new now!