So, I disassembled the 21-4C that was giving me a hard time the other day, and there were a couple of minor suprizes.
One thing was there was a massive ammount of carbon buildup, in the ports there was what I'd describe as a .5 mil thick layer of crud with some actual lumps, on the rod there was a layer of carbon, in the combustion chamber/button head there was a thick layer of crud again around the circle around where the plug sits, and on top of the piston there was an unusually thick layer of crud which seemed to be sort of sandy/uneven in texture.

The sleeve was stuck on the button head, and I mean really stuck, I couldn't get it off it. Is this normal?

Then for the sake of it I measured the lower hole on the rod, and it was 4.99mm from side to side, and 5.05mm from top to bottom, does this say anything about use?

Anyhow, I figure this engine seems to have seen some use? am I right?