thanks for the suggestions all.

I don't think it was the clunk as I had just redid the fuel tank after previously having it cut out a blip when inverted, the clunk was too far back. When I replaced that line, I made sure the brass tube inside the tank was fairly long to help prevent the clunk going forward. I feel pretty good it is in good shape now after reviewing several posts here.

I suspect one of two things: when originally tuned, it was very very hot/humid here. It was probably a bit lean now that it is less hot and less humid (100 degrees 70 degree dew point then vs 80 degrees 40 degree dew point now).

And probably the plug. Plugs seem to be funny, last thing to check as the cause of problem, but in many cases, it's the root of the problem.

I'll do the vertical test as part of normal pre-flight. Does pinching the line at full throttle basically test the same thing (it's easier/safer to do)?

And I'll change the plug.


Tom