first off determine your motor. I got mine from a homelite 26cc weed whipper. simply take the outer casing off the motor to begin.
Step 1: Drive Shaft
I used an old bike axel to attach the bike peg to the motor. initially I squared the bolt to fit into the socket but later you'll realize why that's a bad idea.
Step 2: Mounting the Motor
I used angle iron and 1/4" bolts to attach the motor to the bike. NO WELDING! I did have to grind a portion of the angle iron to account for the flywheel. I used the screws from the casing to attach the angle iron to the motor base.
Step 3: Mistakes
the bike axel I used broke. but it helped because I saw a threaded bolt underneath the socket.
Step 4: Fixing Mistakes
I was able to take the bike peg and drill out the thread in it because it had to fit over the previous shaft. I then used a stop nut and washer to hold the peg. the stop nut is critical. for added assurance I added to screws between the flywheel fins to insure the peg wouldn't spin while riding.
Step 5: Finish
I used an old coat hanger to control the throttle. (not permanent.) and I use the brakes to stall out the motor when I'm done riding.
this was my first instructable. if I wasn't clear enough or you have more questions please comment and I will try to respond.