http://www.youtube.com/watch?v=kBHVuquATDM

This is very much the same but not as bad as the engine shown in the video. It just does it when throttling down to idle speed then wears off even if I set it richer than what is good for flying with. I had a carb problem also too rich in the middle so changed it for an Italian ST V60 carb. Very nice also reduced it but not completely. And when I run it ,it was positioned on it's side. I plan to use it in an inverted position now in another plane a Graupner Extra 300S 63" span. I have a feeling this will induce it. Paul the piston ring I checked and it nice and free no castor build up or any carbon on it or around it also using Model technics Supaglow fuel was thinking I might go for some straight fuel see how that goes what do you guys think. Reading back on this forum I read that one of you guy's are having problems getting rpm out of the same engine. It must be a major fault because mine even with the timing issue it turns a 12x8 with ease Graupner G sonic. Any further help on shimming or general improvement methods are more than welcome.