problems with my baja motorsports go kart?

i recently got a 2008 baja motorsports revenge 150 cc and when i put it in drive and go it like bangs in and out of gear and makes a grinding noise but it works fine in reverse and it pops out of drive when you get going to fast and i was wondering where to get parts on line or if it should be an easy fix and wht might the problem be i thought maybe a gear was bad or something pleasae give me an opinion

Try adjusting the clutch.

Baja Motorsports Blaster Off Roading (Short Version)