The seller sums this bike up better than I probably could: “This is the answer to a question nobody asked. Its a BSA B50 single in a Yamaha RZ350 chassis. I can say with 100% certainty you will never find another, and you will be the only person out there with one in the entire world.”
He continues by saying, “the bike is a homebrew creation with plenty of one off machined aluminum bits. It is actually pretty well done and well thought out. I should probably keep it for novelty’s sake but I can’t keep them all. The bike fires up and runs and rides but it hasn’t been regularly ridden for a couple years. It will fire up first kick if you know how to start a British single cylinder, and it pulls like a freight train. The bike is what is, and its neither a B50 or a RZ350, but its quite possibly the coolest moto-hermaphrodite you’ll run across this year. The bike has a clean California title with both the Yamaha frame VIN and B50 engine number on it.”
I had to look it up – claimed output of the original RZ motor would have been 52 horsepower and 30 ft-lbs of torque per this Cycle World review. It’s unclear what year this B50 motor comes out of but the 499cc air-cooled single was typically good for around 34 horsepower and 28 ft-lbs of torque. It’s a crazy concept – would you ride it?
Find this odd pairing in Grass Valley, California with a BIN of $1,600 here on eBay.