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Manufacturers kept plugging away at roughly the same recipe for decades until Yamaha released its YZ400F four-stroke dirt bike, which won its first race (1997 Las Vegas Supercross) with relative ease.
A stroke is the action of a piston travelling the full length of its cylinder.In a two-stroke engine, one of the two strokes combines primarily the intake stroke and the combustion stroke, while the other stroke primarily combines the compression stroke and the exhaust stroke, though technically since both ports are exposed during both the combustion and compression strokes, some reversion ...
The four-stroke engine is more efficient when running at full throttle, while the opposite is the case for the two-stroke engine. When a small car under heavy load runs at half speed, the engine automatically switches to the two-cycle mode, which is then more efficient. The research on this showed a 27% reduction in fuel consumption. [8] [9]
Engine 499 cc (30 cu in), 2-stroke, four-cylinder, liquid-cooled, reed valve induction with YPVS Bore Stroke 56.4 mm × 50.0 mm (2.22 in × 1.97 in) Compression Ratio 6.6:1 Fuel System Mikuni VM26SS 26 mm (1.0 in) carburettor x 4 Lubrication Yamaha Autolube two stroke injection, transmission gear pump. Ignition
The Yamaha PW50 is a commercially available two-stroke 50 cc (3.1 cu in) mini dirt bike, designed, developed and produced by Japanese manufacturer Yamaha since 1980. [ 7 ] [ 8 ] [ 9 ] References
The Kawasaki KX100 is a two-stroke motorcycle made by Kawasaki, positioned between the 85 cc and the 125 cc classes, with 19 inch front and 16 inch rear wheels, compared to 17-inch/14-inch typical of the 85 cc motocross bikes. Longer travel suspension and larger bore size main differences between these bikes which otherwise are the same.
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.
The engine has a single rotor that spins on an eccentric shaft in a peritrochoid (Mazda uses an epitrochoid) housing. [38] Since the stationary/rotor gears ratio is 2:3, the rotor rotates by 360° every three rotations of the crankshaft. The eccentric shaft runs on plain bearings, [38] which were better than rollers for heat dissipation ...