As Neat Times found out, im using a setup from an old pedalmoped.
The belt pulley on the left side, have on the backside a chainsprocket who freewheels, or when in locked position, dont freewheel. The pulley is "similar" to a jackshaft.
The engine (centrifugal clutch) engage the pulley by belt, with pulley/sprocket not locked, no power to the chain to the rear wheel, or pedals. Pulley spins free. Locked sprocket (knob on pulley)engine transferes power to rear wheel.
Unlocked when pedaling, pedal chain (right side) transferes power to rear wheel, and trough the chain on left side to the sprocket on the pulley, who freewheels,not spinning engine.
Locked you engage the pulley by pedaling trough the left side chain/sprocket on pulley, trough belt,C.clutch, and the engine will rotate/start.
Pedals are only connected to the rear wheel by its chain, not on the pulley, the shaft just go trough it, and i can backpedal to engage rear brake .
At pedaling just chains & frewheel sprocket would be engaged when unlocked, not in a need om turning engine also.
MeasureTwice, yes its existent on Peugeot 102/103 and Motobecane mobylette. Found the idea by surfing around trying to find out which engine i´ve bought......Could say some about French´ones, but this was a nice idea.
NeatTimes, NO, im not using a belt tensioner, dont need one, the C.clutch on the engine would not engage the drivepulley not under power,
The clutchsystem is of 2 different parts, one by arms who engage quite fast (slow rpm)by centrifugal force when pedalforce,(if drivepulley is locked!) who will connect and start the engine, and another centrifugal clutchsystem who connects on higher rpm´s, engaging the drivepulley, and locked sprocket to drive. And i got a freewheel rear wheel pedalside sprocket,yes.
When starting the motor, bike on the stand, locked drivepulley, and (hopefully enough..) one step on the pedal,nearly as an kickstarter. Unlocked just pedal way..........
Heres a exploded view of a Motobecane drivepulley,and an Peugeot engine centrifugal clutch, who could show a little more.