I just bought a few big reds and get on of them goin yesterday. Suprisingly it runs beautiful. I rinsed out the gas tank and filled it with clean stuff and had my dad pull me in 4th gear so we could get it started. It now starts and runs great. However, I give it gas and only the left rear wheel spins. So it spins out cause its only one wheel going. Anyone have any ideas on this? Do I need to swap out the rear end? Is there something wrong with the drive? I can go through all 4 gears no problem. Please help!

 

Sounds like the spline is gone on the hub that is not driving, jack up the bike and see if that wheel spins freely in gear. If it does you will need to get either a new hub, most likely, or a complete rear shaft.