This is a wet clutch which works both centrifugally and manually. Pushing the shifter (rocker front and back) disengages the clutch and selects the gears. If you leave it in gear then it will idle in that gear until you give it some throttle and then it will accelerate.
Heel push=1st gear
Toe push=neutral
2nd toe push=2nd gear
3rd toe push=3rd gear
Pushing the gear lever disengages the clutch which also works centrifugally when you do not push the lever regardless of the gear chosen.
So the clutch is both centrifugal and manual.
http://en.wikipedia.org/wiki/Honda_Super_Cub
regards
Mech