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Twenty years ago this month Yamaha dropped its game-changing four-stroke MXer bombshell, the YZM400F. The prototype set the precedent for a bold new era of four-stroke machinery. Aboard the prototype Doug Henry won the final Supercross round of the 1997 season in Las Vegas. Henry returned the following year aboard the production version YZ400F to claim the 1998 Outdoor National Championship. A Supercross championship for a modern four-stroke MXer wouldn’t be accomplished, though, until Ricky Carmichael’s 2006 championship season aboard a Suzuki RMZ450.


Yamaha Debuts All-New Four-Stroke YZM400F

By MO Staff Jan. 8, 1997

Yamaha released information today on a ambitious new project that will see the company go head-to-head against two-stroke motocross machinery in 1997 using a revolutionary new ultra-lightweight 400cc four-stroke MX racer.

Yamaha apparently decided to develop their innovative four-stroke off-road technology in an effort to stay ahead of growing environmental concerns over two-strokes and pending legislation that may ban the use of two-stroke motorcycles on public lands in the near future.

The company plans to field YZM400’s in a full factory effort in this year’s AMA 250cc Outdoor National Series, as well as entering machines in select world championship motocross grands prix in Europe.

Veteran MX racer Doug Henry has been contracted to ride the bikes in the AMA series for 1997.

According to Yamaha Motor Corp. USA Public Relations Manager Scott Heath, there are currently only two prototypes of the YZM400 in existence. “Both machines are in Japan right now undergoing further development,” said Heath. “Additional machines are being produced, and we plan on having two factory works bikes for our 1997 AMA program.”

Bristling with several advanced technological features, many of which have patents pending, the new machine “will meet the minimum weight requirements for the 250 class,” according to Heath. Although details are sketchy at this point, it is known that the compact, lightweight 397cc single-cylinder four-stroke engine features a DOHC 5-valve cylinder head, liquid-cooling, a four-speed transmission, and will produce “over 50 hp,” according to factory claims. Chassis and suspension are based on modified YZ250 components.

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