I haven't started accumulating parts yet...I trying to do as much research as possible beforehand.
Is it possible to change springs in a clutch to change engagement rpm?
Another possibility I've been considering is using a standard Briggs engine and using a small gear reduction box much like Harley does with their trannys. This way, the clutch could be mounted to the engine output shaft, and primary chain drive to the gear box, secondary chain to the hub.
Depending on the clutch, there are usually springs that can adjust the engagement rpm- but down that far- I don't know. Gear reduction engines are usually used in applications where a centrifugal clutch is not used. I have never seen one go that low- might be out there though- I'm not saying I know the universe of clutches.