ive done this with the 2nd gen of 31cc 4 strokes. you take off the clutch, starter, and most of the front housing (cutting is required, cut all the plastic that isnt the cooling shroud) you should have the flywheel visible. get a 1/2 black iron pipe nipple, about 1 1/2 in long, chew it up with a grinder,(extra traction) and put it over the shaft, grab a 3/8- 24 nut, and some washers, and clamp her tight. than get some angle iron, or c channel, attatch them to the metal mounting ears of the motor, so you have 2 going straight down. deflate the tire, and put the weedeater assy, on the bike. mark where you have to cut the metal "legs", and bolt of weld to it to the bike frame, pump up the tire. it will be pedal to start, and break or kill switch to stop. my top speed is 28 mph.