If you're tired of paying astronomical gas prices or just looking for a fun, cheap ride around the neighborhood, weed trimmer powered bicycles are a great way to get around, especially if you are under the legal driving age. They attain an average speed of 20 to 25 mph and can get up to 250 miles to the gallon.
Items you will need
Bike--simple frame, no rear shocks
Weed trimmer motor (the smaller the better, preferably with mounting holes and a clutch)
Welder
Tension
4 metal straps with mounting holes
Grinder
Wheel sprocket
1 metal end stop
6 to 10 metal bolts, matching the size of the holes in the mounting straps
2 feet of spare bike brake cable
Step 1
Remove the rear tire. Install a large sprocket on the left side facing outward. Bolt the sprocket on from the outside with a washer. Then weld a small sprocket, with 10 to 12 teeth, to the bell housing of the clutch of the engine. Make sure it is centered.
Step 2
Weld two metal straps behind the seat or under the center bar, wherever you have enough room to place the weed trimmer engine. If the straps have holes in them, you can bolt them to the frame. Leave just enough distance between straps to hold the engine box.
Step 3
Mount the engine in between the metal straps with metal bolts. If you do not want to use metal straps, you can drill holes in the motor and bolt it to a plate that you weld to the frame.
Step 4
Wrap the bike chain around the newly applied wheel sprocket. Tighten the sprocket ring with a tensioner.
Step 5
Unhook the brake cable and attach it to the carb throttle of the motor with a metal end stop. You may need to add two feet of bicycle break cable to the weed eater throttle cable with the end stop to make it long enough. Once this is done, you are ready to ride.