I recently bought a nice used '06 from the second owner who had the bike for about 6 months... the bike looks to have low hours (hardly any wear anywhere), all stock except FMF slip on and recently installed 6.15 flywheel. The guy I bought from was meticulous with his bikes (this was his "extra" bike - he has a bad ass KTM 350 as his main ride and a couple bikes for his kids) and he recently rebuilt the top end with new cylinder, piston, rings, timing chain, etc. He put an hour meter on after the rebuild which read just over 4 hours. He said the valve train was still in great shape, valves never out of spec, etc, so he left them as is. He runs full synthetic in all his bikes, the bike starts first or second kick every time, hot or cold, runs good, crisp response, etc. Here's my question: I took it out for the first time last weekend and noticed a vibration on deceleration. I never noticed this when I test rode at his house. Could this be a bad crank or main bearing? timing chain or tensioner? the heavier flywheel?? or is this normal? I've owned Yamaha four strokes in the past (a couple 426s and a 250F) and have never noticed this type of vibration before, even on my CRF450. It wasn't arm numbing, but just enough to be noticeable. I put about 6 hours on it last weekend in the desert and it ran fine. I checked the engine mounts and all other nuts/bolts and every thing was good. I'm worried now that I bought a lemon Does anyone have any insight on what this could be?? help!