Yamaha has just revealed its all-new YZ85 two-stroke motocross machine – which use Yamaha’s Power Valve System (YPVS). Plus, it has also revealed the return of its iconic YZ125 and YZ250.

Our friends Young Machine, Japan has just sent us details of Yamaha’s all-new YZ85 two-stroke competition motocross machine which uses YPVS. But what is YPVS? Well, it is actually fairly old technology, first implemented by Yamaha back in the late ‘70s. Basically, Yamaha engineers realised that by altering the height of the exhaust port they could effectively change the engine power delivery – and consequently offer optimal power and torque across the entire rev range. Clever.


YPVS’s balances power and torque using a valve at the exhaust port of the cylinder and rotating or sliding the valve in conjunction with the engine – controlling the timing of the exhaust. The valve drive control is done based on information such as the engine speed, the throttle degree, etc.


Interestingly, Yamaha was the first company to produce consistent results with their YPVS system in its race bikes – giving them a great advantage over other manufacturers throughout the late ’70s and into ’80s.Yamaha’s reintroduction of two-stroke technology is a very exciting development – and we’ll be keeping a close eye on how the iconic Japanese brand moves forward.

YZ series project leader Daisuke Sakurai said: ‘There are many merits to two-stroke, especially for the beginner. But most importantly, it’s fun.’


Ross Mowbray
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