IM 15. I know alot about engines and how they work, so im not a retard or anything. My dad bought me a YS91 last year for christmas and ive been flying it ina midget mustang. very good combination. very fast, very predictable. i was running a 15/6 on it and it went fine. Had a run in at my high school, apparently planes and trees dont mix well. Took the engine apart to check or damage or any sand or whatnot. put it back together no problem. Ran it again in my new midget (totalled the last one) and something wasnt right. low end was fine, but the transition was another story. It kept seizing up everytime. settings were all the same as before the incident so i check the valve lash. way off. fixed ran great. I then proceeded to race some guys at the feild and i was not keeping up. i noticed one had the same engine only a 15/8 prop, the other running a saito 100, not sure of prop, but i should have been able to keep up with them, if not pass them. no contest. i switched to a 15/8 that very day. tached it and peak rpm was about 7500. i know it can do beter then that. ive heard with that prop it should be turning around 9000, which with the 15/6 it was turning around 11 grand or so. something wast right. made the mistake of flying anyways that day. took off around half throttle as usual, but after about 3 sec. it went lean and quit. hasnt run the same since the crash. wondering what to do. and if anybody else is flying a similar combo that could give me their rpm range.

thanks,
ken

With a 15x6 the 91 should run well over 9000 rpm. Something is bent from the crash, but it's impossible to tell without seeing the engine.

Dave

we figured either that, or the piston is bad