The handlebars have a nice bend to them and are well-placed for good rider control and legroom. In fact, the entire ergonomic package on this YZF is well thought out. says that "The gas tank is reasonably thin and allows good forward and backward movement while providing something nicely shaped to hold onto with your knees. In 2002 the blue painting was stopped and left to a bare aluminum look. Carburetor tuning was modified to deal with starting and off-idle take off difficulties.Īlso in 2001 the subframe was changed from a steel to a blue painted aluminum style. Yamaha also designed a new exhaust pipe design so that exhaust header removal would no longer be required when replacing the oil filter. The suspension also received a bit of an overhaul with the goal being reduced weight and smoother action throughout the stroke. The crankshaft was also reshaped and the whole assembly was redesigned for quicker throttle response and, Yamaha claimed, "less high-end horsepower loss." In addition to motor modifications, a few changes were made to the transmission to help contain the power and ensure longevity. The new valves were more than forty percent lighter than the previous valves, allowing for lighter and softer valve springs, in turn allowing a quicker revving engine, improved throttle response, higher rev ceilings, and more power. The next year, in 2001, Yamaha replaced the previous steel valves with titanium ones. In addition, the carburetor and jets were updated to ease the YZ400F's starting woes.
In 2000, Yamaha updated the YZ400F, increasing the displacement to 426 cc for greater power and throttle response. Titanium five-valve, 426 cc, 95mm x 60.1mm stroke, compression ratio 12.5:1 Type of motorcycle Second generation YZ426F Production
This victory is considered by some to be the major turning point in the motocross world-for the first time, four strokes were considered a competitive racing machine. In 1998, Doug Henry won the AMA National Motocross Championship aboard the YZF, becoming the first rider to win a championship on a four-stroke motorcycle. The 1998 YZ400F was the first bike to come stock with a Keihin FCR carburetor. It benefited from engine compression braking, which allowed the engine to slow the bike down during deceleration, giving the brakes a rest. The bike had an 11,600 rpm redline power and torque close to its 250 cc two-stroke rivals. It was "the first modern production four-stroke motocrosser that was directly competitive against two-strokes." Initially, Yamaha targeted a dry weight of 233 pounds (106 kg) (on par with the 250 two-strokes of the time), but by production, the bike weighed 250 pounds. Yamaha introduced the YZ400F in production in 1998 after a successful AMA season in 1997. Type of motorcycle First Generation YZ400F Productionįive-valve, 400 cc, compression ratio 12.5:1įirst generation: YZ400F 1998–1999 The YZ400M was the predecessor of the production YZ400F, which was released the next year. This was the first time any four-stroke had won an AMA event. Doug Henry piloted the YZ400M to its first victory in 1997 at the Las Vegas Supercross. The YZM was far ahead of all competition among four-stroke motocross bikes. In 1997, Yamaha rocked the motocross world with the introduction of the YZ400M prototype, a concept motorcycle which borrowed much technology from road racing.
It solved the power dilemma by borrowing superbike technology and giving the YZ a five-valve head, liquid cooling and a 12.5-1 compression ratio. The Yamaha YZ400F was developed to fit into this category. Yamaha engineer Yoshiharu Nakayama first came up with the idea of creating the first competitive four-stroke race motocross bike. In 1996, the AMA changed racing rules to allow 450 cc four strokes to compete in the same racing class as 250 cc two-strokes. Most riders considered four-stroke engine technology to be largely utilitarian and uncompetitive, relegated solely for trail riding. AMA racing classes had two classes: 125 cc and 250 cc two-strokes, with no provision for four strokes. 8 Seventh generation YZ450F 2018-Presentįor many years, the motocross world almost exclusively used two-stroke engines.
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