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The original YZ250 of 1974 used an air-cooled 250cc two-stroke engine of 70 mm bore and a 64 mm stroke, which was improved semi-annually. The air-cooled motor was replaced in 1982 with a 249 cc liquid-cooled two-stroke reed-valved engine with a mechanical, rather than servo-driven, YPVS exhaust valve for a wider spread of power.
Yamaha YA-1. YA-1 built August 1954, produced January 1955. The first bike manufactured by Yamaha was actually a copy of the German DKW RT 125; it had an air-cooled, two-stroke, single cylinder 125 cc engine [1]
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In 2003 it received an aluminum subframe, which was replaced in the 2006 model with an all-aluminum frame. The YZ250F has been praised for combining the broad-power characteristics of a four-stroke engine with the light handling more common in smaller, 125 cc two-stroke motorcycles.
In addition, the cylinders received a so-called Yamaha Power Valve System (YPVS). The first model series (TZ 250 A) of the water-cooled twin with contactless thyristor magneto ignition had a power output of 51 HP, the last expansion stage [clarification needed], the TZ 250 A (3TC) from 1990, 76 HP.
Kocinski at the 1990 Japanese Grand Prix. 1989 was also the year of his 500cc World Championship debut. In 1990 he raced in four different championships, but the highlight was winning the 250cc World Championship in his first full season on a Team Roberts Yamaha YZR250. [1]
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Model Constructors' championship; 1973: 0W20: Liquid-cooled, inline-4, two-stroke engine, chromoly frame. Yamaha's first 500cc factory bike won from the outset at the first round of the 1973 season, ridden by Jarno Saarinen. 2nd 1974: 0W23: Yamaha's first machine created specifically for 500cc racing.