Not to sound like a know it all, but I'm pretty good with those nasty little buggers(nitros in general), but I have in my time run into the exact same experience as Jeff & bono(with the Traxxas mills). You can tune and check for leaks for days and it'll run exactly the same! I'm not bustin' on Traxxas but I've heard this same story sooooo many times. Seems some were good engines and some weren't. Even a good one is very sensitve to proper tuning, moreso than most! I gave up and got an OS18TM. Been ear to ear grinnin' ever since! I here there's a 21 TM now[>:]!