For a friction drive motorbike, how big is the difference in cc's. Im having trouble finding a 30+ cc weedeater with a rear or back pull start. (so i can still pull start the thing once mounted) Ive found a bunch that were 25-28ccs with the rear pullstart. It will be mounted to a somewhat heavy bmx bike and im about 190lbs. Would a 25cc motor work well enough given the weight?