Here is my take on the Tom Thumb minibike plans on this forum. I really didn't NEED a minibike but I wanted to learn how to TIG weld (still a lot of learning to do....). There were some modifications of the plans; the handlebars are taller, there are footpegs and footpads because there at nearly 6 feet and 60+ years of age this was the only way I could ride it. It's also wider because I am (somewhat) wider than the skinny kid who originally made one. There is a brake; the hub brake/sprocket adapters are homemade, the wheels/tires are Harbor Freight, the engine is a 47/49CC Chinese engine with a transmission so no jackshaft was needed. The gas tank is PVC fittings and the seat is homemade and was then upholstered by an auto trim shop. I welded on a kickstand. I really tried to DIY everything because just getting a kit or buying off the shelf and screwing everything together is just not very satisfying.
The tools I used were fairly crude; MIG/TIG welders, a bandsaw, angle grinders, a chop saw, tube notcher, and the low-end HF pipe bender (that I bought used cheap). It was impossible for me to go much more than 90 degrees so this was done by cutting and welding the curves. This was difficult and tedious. The bends on the back were just BARELY done with sand and BB fill and constant repositioning. The cables were off the shelf but I had to cut them and remake the throttle cable end. I had a waste factor of about 2x on the pipe.
A lot of this was "barely"; the front tire barely fits; I can barely ride it; the engine barely fits; I barely bent the pipe. The muffler barely fits. in short, I got somewhat lucky.
I originally had a 72 tooth gear on the back and it didn't go very fast but the torque was crazy.
I look fairly silly riding it but all in all it was a satisfying project. I hadn't actually BEEN on a minibike for about 45 years until I rode this.
