|Engine||348cc two-stroke twin-cylinder|
|Bore / Stroke||61mm x 59.6mm|
|Top speed||99 mph|
|Horse Power||34.1 bhp @ 7,000 rpm|
|Frame type||duplex cradle|
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Honda had announced the CB450, featuring a twin-cylinder double overhead cam engine, in the spring of 1965, offering it for sale n the USA from 1966. The technology they used had matured in their GP racing program and they were able to apply mass production techniques to lower the overall unit costs for the production of the quite complex engine. Its sophistication with respect to the British 500 and 650 twins, with which it would compete, illustrated how well Japan had embraced mass-production techniques and how short-sighted the British industry had been in not following suit while it still could.
Yamaha was initially slow to respond, just as they had been slow to introduce the YDS5E, their main development program in 1965 was spent on the tiny AT90 twin. But during 1966 the new competitor to the CB450 began to take shape, and it went on sale in the USA early in 1967, alongside the YDS5E and the YCS1.
The YR1 was a mixed bag. It was a milestone in that it was the the first Yamaha two-stroke twin to adopt the horizontally split crankcases that would become common to the whole engine range. The engine layout followed the standard developing now for the twins, with the clutch on the right-hand end of the mainshaft, and the primary gear and Autolube pump on the right-hand end of the crankshaft, alloy barrels with cast-iron liners fed the two Mikuni carburetors of 28mm diameter on the 350. But in many ways it was also a massive disappointment. The cylinders were regular three-port, and the performance was no better than adequate, just managing to break the magic ton of top speed, and quarter mile just under 15 seconds. Styling was also very reserved, clearing aligned with the dreary styling applied to the YCS1 and YDS5.
This had been Yamaha's opportunity to stun the world with an outright fire-breathing race-bike for the street, reflecting their successes on the racetrack, but instead it seemed more like a steady tourer. Actually, it was in many ways a two-stroke equivalent of the CB450, so perhaps that was a deliberate choice. The chassis was essentially a larger version of the YDS5 frame with the more powerful brakes, thanks to new drum linings. Suspension was quite firm, and steering neutral. The YR1 was a decent bike, but it could have been so much more.