Chain Vibration?

Chain tension and alignment is critical.
Also if you're using the kit supplied #415 chain (you didn't tell us what engine you have) that most Chinese 2 strokes use, it can be a source of rough running. They sometimes have kinks, twists or binding links which transmit into vibrations or general roughness.

Dressing, or filing the rough edges from the rear driven sprocket teeth and proper lubrication is also a good idea to achieve a smooth running chain drive system.

Tom