New head assembly arrived, new check valve fitted, valve clearance set in the middle of the range (about 0.05mm) to allow for some settling in and out to the field I went.
First impressions were a bit of extra oomph at lower throttle settings but no spectacular change on the tacho at full noise. 5 minutes in the air later I'm creeping up the throttle position a little more each pass as the power is dropping off, then the misfiring starts all over again. Land it, shut it down, spinner back plate is cool and the cylinder is cool enough to hold for a few seconds without burning yourself. Bit more needle and reg tweaking and a few more ups and downs and nothing is getting better so called it quits for the afternoon. Odd thing is that the leaner I went the more responsive the engine became, and the earlier it began to misfire..
Pulled it apart last night to replace the ring seeing as I had one in stock, and the crankcase and valve lifters were full of fuel. Had a real close look at the throttle body and butterfly seal and couldn't see/feel anything obvious. Pressurised it underwater and nothing leaked where it shouldn't, and reassembled it all with new o-rings, gaskets and carb insulator.
Took it out at lunch today and same thing, cruising around to bed in the ring, with the occasional upline to clear things out and 5 minutes later, I'm inching up on the throttle as the power starts dropping off, then the misfiring starts again.
The oil underneath the plane is as clean as it went in, usually it's lightly speckled (running 10% coolpower) under there with slightly darkened (but not burnt) oil.
I'm stumped how an engine that can run so well for so many years, can become unreliable within the space of 1/2 dozen flights with nothing obviously broken.
I've got some choice words I'd like to use to describe my feelings on the matter, but "very disappointed" is close enough for now.
Last edited by bjr_93tz; 03-15-2017 at 08:49 PM.