Hello, I just joined. I couldn't find anyone mentioning severe vibration in the forum. I've got a chinese "80" cc engine on an old Giant mtn bike. My brother has the identical motor on an old Schwinn mtn bike. They both produce hand (and crotch) numbing vibration between 15- 22 mph. This vib. goes away at higher speeds. At lower speeds it's still there but not as intense. Any ideas? Thanks, Joe. nevermind, I just found a couple of relevant threads.