Raf, make that an engine in good condition with fresh fuel and .... as there could be many more reasons.

Actually there are a lot of reasons, engine conditions, old fuel, filling the muffler with fuel when he fueled the helo, either end not carbed right... And the enfine in good condition can include bad bearings and the front bearing seal, a number of carb issues, loose head screws, glow pug, and backing plate screws.... alot of things.

But the original poster had already found his proble by thesecond post here on this thread so it didn't matter. I probably shouldn't have posted and let this die but I was curious why Bug answered, nothing more, and I pissed him off. Luckily he has thick skin and can take it.