Just thought I'd throw this idea out there to see if anyone has tried it. The rear axle on riding lawn mowers is pulley driven seems like ya could throw a lawn mower engine in front of it and atatch it as a push trailer thereby curtailing the 50cc rule as it would be on the trailer not the bike.
I've seen a lot of these in lawn mower junk yards:
http://www.ebay.com/itm/Foote-Trans...396?pt=LH_DefaultDomain_0&hash=item417861df9c
I've seen a lot of these in lawn mower junk yards:
http://www.ebay.com/itm/Foote-Trans...396?pt=LH_DefaultDomain_0&hash=item417861df9c