I have started makeing this instructable since I cant find anything nice on how to make a cheap motor bike. so here it is (my cost was ONLY $30) but i already had the motor and some other stuff. you will need to read through this whole instructable before you start also this is my second instructable so i may have forgoten something so just leave a comment. you should reach speeds up to 30mph depending on weight and ratio and the size of the engine.
you will also want to check your local laws to make sure it is legal! and stuff
it is better if the motor you are using doesn't have a clutch if it does then remove it. now take off all the plastic on the motor that doesn't need to be there mainly just over the flywheel. then if your motor doesn't have a clutch remove the cover over the crank shaft, not the crank case! it will take lots of effort, it helps to use a hammer. then take your bike peg and see if it fits the threading if it does your lucky, if it doesn't take the cover to a machine shop and have it threaded to fit the peg this is what i had to do
set up the kill switch on the handle bars i just went and used the kill switch from the motor and extended it with some normal electrical wire from home depot. the throttle is very tedious to connect and is different on every motor, so your on your own then but use the rear brake lever for and cable
now your done go impress everyone thats has been doubting you to start you just peddle and give it some throttle and keep peddleing when you are going slow just to keep the engine from stalling. please comment and rate! my motor just died so i am replacing it then i will post a video of it working.