Maybe the beginning of the end for two-stroke motocross bikes here in the United States was the decision by Kawasaki a couple of years ago to drop the KX 125 from its U.S. line-up. Today, as you may have read, American Honda has advised its dealers that the 2007 model year will be the last year for two-stroke Honda motocross machines here in the United States. Of course, several other manufacturers continue to offer two-strokes.
Honda appears to be the first to market with a 150cc four-stroke motocross bike — intended to take the place of 80 and 85cc two-strokes. The other manufacturers are hard at work on four-strokes of approximately 150cc, as well, however. This will mean four-strokes will dominate every major motocross displacement category here in the United States before too long.
Aside from emissions issues, the torque and power delivery of four-strokes tends to make them easier to ride/race. Maintenance, however, can be significantly more expensive with four-strokes than with two-strokes. Valve trains, for instance, have been problematic on some of the smaller displacement four-stroke motocross bikes (250cc), but the reliability of these machines is continually improving.
If you had told anyone in the U.S. motocross industry in the late 1990s that two-stroke production machines would largely disappear within a decade, they probably would have laughed at you. This has been quite a revolution.
