The clutch
The clutch allows the scooter to idle with the engine running by isolating the rear wheel from the transmission. It operates in much the same way as the variator, being of a centrifugal design. As you twist the throttle, the engine increases its speed and the belt drive spins the clutch. As the rotational speed increases, centrifugal force causes the clutch inner to expand, and begin driving the clutch outer, which is connected to the rear wheel.