Last year this engine started this weird 4-cycling behavior, worse at full throttle (WOT). Its not consistent. I can sometimes almost tune it out o the ground, but those same setting sputter terribly in flight. I even took the silencers off, no change at all, just louder.
Yesterday at the field this was just constant and not reassuring. I tried retuning it, and this was the best I got on the ground. In the air it worsened. I should have taken notes last year, when I took the engine apart looking for any issues. Not sure if I changed the spark plug but it would have been on the list. I haven't changed the ignition. It sounds to me like an air leak that leans out the fuel mixture as altitude increases, but then richening it should lessen the sputter; it doesn't. Any ideas are welcome.
I have benched it and will be once again looking for issues, will change the ignition and the spark, see if another carb I have will fit. Something happened to this once perfectly running engine, I have no idea what.
Took the silencers off. No performance improvement, just much louder.
These do bring the noise down.
Back on the bench... will drop the engine and try again.
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