Thanks - that makes more sense: they have a centrifugal clutch (strangely at the rear), in addition to the variable pulleys (with the control at the front as it should be). As I recall, snowmobiles just let the belt slip on the input pulley until the engine turns at high enough speed to cause enough clamping force (they even call the pulley control system the "clutch"), and this is much better. That clutch (mounted at either end) is certainly not required - or wanted - with an electric motor. A non-slipping belt-type CVT might work well, keeping the motor in a more useful speed range, although with the right motor it isn't necessary.it's the front, the rear is just spring loaded.
what's different to the systems I know (mopeds), is that the clutch is at the rear and not at the front.