Could be hand shifter is in Neutral or one of the centrifugal clutches are slipping. The machine on the front of the engine has both a centrifugal clutch as well as a standard clutch actuated by solenoid.
verify gear selection is not in Neutral first and then as long as it is in gear it should go, if not I would look at the front solenoid (clutching) to make sure it is not separating the pack. If it is not then time to go in the front cover to inspect the clutches.