We spotted this 1975 Yamaha YZ125B for sale locally, and it got us to thinking about the tuning fork company’s early years in the 125cc motocross class.
Just a year after Yamaha stood the burgeoning 250cc class on its ear with the introduction of its blazing fast YZ250, Yamaha unleashed its first ground-up 125cc motocross design in 1974, the YZ125A. This screamin’ baby demon took its styling cues from its big sister, right down to the unique saddle-stitched tank halter that helped hold the fuel tank on the bike. The story of that unique feature is a good one all on its own, as it was actually a mistake of sorts, invented by Don Jones, the father of three-time AMA 250cc National Motocross Champion Gary Jones, back when the Jones family was instrumental in the development of the YZ250. In a rush to send the prototype for what would be the YZ250 to Japan, Jones realized he needed a way to secure the tank, so he sent sons Gary and Dewayne to the local tack shop to pick up some horse bridle material that he fashioned into a halter to secure the tank before crating the bike and shipping it to Japan. The stop-gap item was never meant to be used for production, and yet when the first YZs hit American shores, they did so with the tank halters in place.
But we digress.
However, there simply wasn’t enough time to bring the new YZ125 out for 1975, so Yamaha soldiered on with what went on to become one of the rarer YZs in existence, the 1975 YZ125B. While Yamaha could have refined the YZ125B, most of its R&D efforts were already focused on the bike that would replace it. Thus the YZ125B was basically a YZ125A painted yellow and black, beginning the legacy of Yamaha YZ color schemes that we wish the company still used for its YZ models today (fortunately, we do get those colors back every 10 years when Yamaha releases an anniversary model). The YZ125B retained the original twin-shock rear suspension design with Yamaha’s large-reservoir Thermaflow shock absorbers, and it also retained a few glitches that didn’t put the YZ125B in the most favorable light. In at least two magazine tests, YZ125Bs failed due to faulty idler gears.
But Yamaha knew it had a class killer coming in the YZ125C, which featured Tilkiens revolutionary rear suspension design, now known as the Monocross, a faster engine and better all-around reliability, paving the way for increasingly better 125cc motocross machines from all of the Japanese manufacturers, who quickly left the Euro 125cc models in the dust. Hitting the market as an early-release 1976 model, the YZ125C was available in Yamaha dealer showrooms by mid-1975. The YZ125B’schrome bore was replaced with a more serviceable cast sleeve, and the new engine made more than 20 horsepower thanks to a new four-pedal reed valve and a 38mm Mikuni carburetor that replaced the B-model’s 28mm unit. The YZ125C was a huge success, bolstered when Bob Hannah gave Yamaha its first AMA 125cc National Championship in 1976.
Thus, the 1975 Yamaha YZ125B is rare by virtue of its role as a stop-gap model. Estimates are that only about 1500 of them were ever produced, which could arguably make YZ125B models valuable to collectors, although we wonder if the $3500 asking price for the used model in our photos, which were taken from the Vintage Dirt Bike Swap & Shop page on Facebook, represents the model’s current value. We imagine that’s to be worked out by the buyer and seller.
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