Vintage, classic. This mini bike is souped up with a torque convertor. There are two plans - the first uses a junked bicycle for parts, and the second is the super old-school traditional mini bike style.
We've also found a lot of good information on free mini bike plans at the DIY Go Karts website.
Take a small kart engine, add a slick variable-ratio belt transmission and you'll have a real performance 'bear' for half the cost of a commercial motor scooter.
On flat ground this scrappy little mini bike can hit around 30 mph. And when you come to a hill, the torque convertor will automatically downshift to a lower drive ratio to give you rugged hill-climbing power.
The best part is the machine's lightweight, low-cost design. The basic frame comes from a discarded 26-in. boy's bicycle, which you can usually pick up for a few dollars at a bike shop or junk yard. Most of the parts are stock bike or kart items, easy to come by and easy to assemble. Even if you start with a new engine, the entire scooter can be built on the cheap.
A simple mini bike is a great way to get you and your kids working together. You'll both learn a vast amount about small engines. It's a great way to encourage mechanical ability in your children. And if you give them a budget for custom work, watch thier imaginations fly dreaming up cool accessories and doodads.