I've seen centrifugal clutch kits too on ebay. Some are marketed as 'duel start'. I know that to start a centrifugal clutch you need a pull starter...but maybe the duel start kits can be pedal/pop clutch started as well. I would assume this is through the use of a locking clutch? I see these kinds of kits on the grubee website. Grubee Inc.
It's under the skyhawk engine kits. Has anyone here used one of these?