Yamaha Bucket Racer

Here's a little cutie, a bucket racer I built around the mid 80s. It’s a YB90 of early 70s vintage. I bought the bike for around $30 from memory and bought another from a wrecker for parts. The YB eventually morphed into the YB100 with a whopping 100cc of raw power, it had a pressed steel frame, and a 90cc two stroke motor. The carb is hidden behind the right engine side cover and feeds fuel into the crankcase via a rotary valve mounted on the end of the crankshaft. Quite a few mods to this little monster: From an old fridge door, using a dolly and panel beaters hammer, I shaped a tail light bracket, a single seat, left hand side cover, oil tank (after the green repaint), air cleaner (seen sticking up on the top of the right hand side cover) and an expansion chamber. Handlebars were made from a bit of 7/8” tube I had lying around. The wheels were stripped and the hubs polished along with side covers and a few other bits and pieces. The speedo was jammed when I bought it and the other bike didn’t have one so I stripped it, freed it up, painted it, made a bracket and installed it on the top pressed steel triple tree. I removed the shrouds covering the rear shocks and front forks to make a feature of the springs, re spoked the wheels and painted everything jet black, later I stripped it and repainted everything in two pack F111 green.
For the motor, I had it rebored, bought a new piston, replaced the big end and mains, re shaped the rotary valve, reshaped the ports a little, shaved a smidgin off the hear, re jetted the carb and made an expansion chamber (ex fridge door). In the background you can see a second frame, I believe Yamaha called these no 7 frames.


Single seat bikes were only $50 to register at the time, but when I took it in the inspector, whilst happy with the seat insisted I drill out the threads either side of the swinging arm, so the rear footrest couldn’t be screwed in (nothing to stop you putting a nut on the end though).


The bike was made using the best bits from each of the two bikes and a lot of manufactured parts. Got looks wherever I went, don’t know if this was due to it’s unusual looks or the noise it made. On full song it created a bit of a racket. Surprisingly for a pressed steel frame, this bike handled extremely well, the motor was quite fast but not as fast as I wanted, just couldn’t find the room to fit a larger chamber without sticking it alongside the rear wheel. But, it was certainly quite a bit faster than other 100cc bikes around.


Again many, many more mods that I can’t remember. Used it as a daily work commuter, a real fun bike.

I also tricked up the motors on a couple of 50cc mopeds: a Honda and a Yamaha. These two instead of getting around 90mpg as was the norm, only got around 40 on full song. The Honda was capable of 50kph standard, after a little work I managed to squeeze justshort of 70kph from it.