There is one other reason not to do a bike with that engine. If you spend any time in the Laws and Legislation forum you will see that Illinois has very strict laws on motorized bicycles. Most obviously, a 1 HP limit
on engine size. Lots of guys run 66 cc 2 cycles and others the 49 cc Honda clones. Even though all of those are above the 1 HP limit, they are not so freakin' huge as to be painfully obvious to any cop observing you.
Build what you want, but understand you are begging for trouble.