Clutching???

In short the primary is rpm sensing and the seconary is load sensing. the weights in the primary are forced outward via rpm and centrifigal force. the heavier the weight the more outward force is applied to the roller causing the sheave to clamp on the belt. The spring works aginst the weights. The profile and shape of the weight affect how much force is applied and there are endless combinations and setups.

A good read for clutch tuning would be "Olav Aaen's Clutch Tuning Handbook." I have read mine cover to cover atleast 3 times and refer back to sections all the time.