The petcock was replaced about a week ago, but the replacement failed. Decided to just put a manual fuel valve on instead. Installed manual fuel valve and a new carb. Same issues.. Adjusted valves again (valve gap one increment less on intake+exhause), same deal..
So the piston ring suggestion was dead on. I ordered a piston kit and a set of gaskets over the weekend, so I pulled it apart this evening. I removed the piston, and found that the top compression ring had a very small piece snapped off:
Luckily that piece was still in the ring groove and not in the bottom end...
The piston also appears to have a small crack between the two compression rings:
Crack is on the right edge of the carbon line in the pic above.
I'm really surprised to see that the ring is cracked. After researching a bit it seems that ring gap is frequently off when these come from the factory, so I'm figuring that the ring gap was just too small and it ended up cracking off.
The good news is that the jug looks good. No scoring, no scratches, and cross-hatching is still present. Next week I should have the gasket set in from China. I'll install the piston, new gaskets, and throw it back together. Then I just need to drain the synthetic oil and do the hard break-in
Thanks for the help on this!
Rob