There can be a few things that cause this, however, the most likely cause is worn springs in the outer clutch basket.
If the springs are too loose this can allow the outer basket to spring back and forth on the ring gear when the bike is launched, resulting in the bike being very erratic. We recommend that you have the basket inspected for excessive wear.
MTC can rebuild some stock baskets and can upgrade many applications to a heavy duty billet basket. Please contact us for details.