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 Build
LAT OUT, this scrappy little motor
scooter will hit up to 32 mph on a
straightaway. When you come to a grade,
it automatically downshifts to a lower
drive ratio to give you rugged hill-climbing power. Although designed around a
modest 2-1/2-hp engine, its variable-speed
drive enables the PM minibike to equal
or exceed the performance of many commercial scooters selling for twice as much.
In most states, it can be licensed for road
use with no difficulty.
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 for $100 to
$120. With a used engine, the cost is considerably less.
Special features include a two-passenger
cushioned seat, a motorcycle-type twistgrip throttle and a novel, spring-action
front fork made by modifying the conventional bicycle fork. The automatic belt
transmission includes not only a centrifugal clutch but also a variable-diameter pulley system that adjusts drive ratio
to load. For road use, lights and a horn
can be added.
Start by cutting the bike frame so you
come out with the portion shown in color
in the drawing above. It’s necessary to
bend the “gooseneck” section of the frame
forward to make room for the engine. This
can be done with a bumper jack as shown.
Bend carefully to avoid flattening the tubing. Heating with a propane torch will
make the job easier.