Ha, if you go back to the first post I opened it up with.

I was already a year in and nearly everything replaced before I started this thread.

On a serious note, towards the end I was worried it was something I was doing wrong, and to some extent one of the issues was something I was doing but it wasn't necessarily wrong according to the manual. If I had purchased a brand new engine I would have run it for x hours, then tightened the valve clearance and may (or may not) have been back to square one with the same problem with a brand new engine.

I know that's what I did with this engine from new and mostly I've been able to tune around it not knowing any better. I had a fantastic run with it for a couple of years with the clearance being on the verge of too tight, but at a rebuild I set it a fraction too tight (but within spec) and the woes began shortly after. Every time I pulled the engine to swap parts it went back together with about 1 thou of valve clearance and I was having problems.

The penny finally dropped when I replaced the head assembly and left the clearances loose for two flights to bed it in and and it ran fine. The valves in the original head were leaking so the new head assembly "fixed" the problem or so I had thought, except the problem came back during the next trip to the field after I had re-set the clearances to 1 thou.

Now I've got the engine sorted I've bought myself a kite to play with. https://prismkites.com/product/hypnotist/