Vintage Mini-Bike Build
This little gem is a 1973 Western Flyer model SS300. The bike is indeed mini. Only 48" long and 32" to the top of the handlebars.
There is a spring front suspension that sits below the front steering tube.
Other features include no torque converter, no front brake, and no chain guard.
When purchased, the motor was non-original and not running. It also had a frozen clutch, rusted chain, and no brakes. All of these were simple and cheap to repair.
Because of the Tecumseh to Briggs engine swap, the throttle cable had been previously rigged to work. A new linkage was fabricated with some 1/8" welding rod, which allowed a better way to run the throttle cable.
The exact method to attach a cable to an engine depends on the engine type and style. Lubricate the inside of the cable, and keep it out of the rain!
Remove/Install Centrifugal Clutch
Before trying to remove the old mini-bike clutch, I sprayed the shaft with WD-40 and let it soak awhile.
I removed the clutch unit from the sprocket with a three-jaw puller.
When removing an old clutch, don't force it - make sure you've removed the small set-screw from the old clutch hub with an Allen key. Before installing the new clutch, I scuffed the shaft lightly with fine Emory cloth, then applied a dot of anti-seize.
I'm presently running a 10-tooth clutch with a 72-tooth rear sprocket. With this gear ratio there's decent power coming off idle with a top speed of about 20-25 mph.
Before replacing the old chain, I soaked it in motor oil for about a week, then scrubbed it with a brush. It was a little messy, but it saved me the cost of a new chain.
When purchased, this minibike had a frame-mounted on/off switch. I replaced it with a momentary-off button on the right handlebar. (On magneto-powered small engines, the ignition is always on).
Minibike Rear Brake
Band-brakes are commonly fitted to the outside of clutches or rear wheel drums. A new cable was needed to make it operable again, so I salvaged one from an old bicycle. The procedure was straightforward; the end of old frayed cable was cut off with a Dremel tool, then the outer casing was trimmed down to the needed length.
TIP: Before installing a brake cable, lubricate the inner cable lightly with oil.
After I got the minibike running and stopping, I noticed a vibration at top speed. It seems to be coming from the front knobby tire, which I will be replacing with a sawtooth-tread tire.
You Can't Beat Fun!