Yamaha, the Japanese motorcycle manufacturer, made major changes to its WR off-road bikes in 2007. The 250F and 450F got new aluminum frames, similar to those on the YZ motocross models, reworked suspension, and a new engine design with a built-in sump and enclosed oil passages.
Both models are powered by liquid-cooled, four-stroke, single-cylinder engines. The 250F’s engine has a 249cc displacement; the 450F displaces 449cc. Both have dual overhead cams with five valve heads and Keihin carburetors. The five-speed manual transmissions on both models are chain-driven.
The new suspension system uses Kabaya inverted forks in front, with adjustable preload and rebound damping, and twin-sided swing arms in the rear, with adjustable spring preload and rebound damping. Reviewers thought that the new suspension worked better for woodland trails than the system it replaced, but which was better suited to desert riding. Stopping power comes from 9.8-inch disc brakes in front, and not much smaller discs in back.
Famous for toughness and reliability, the 2007 Yamaha WR met air-quality standards in all 50 states. The new engine struck reviewers as livelier and smoother than previous years. And the new frame made it less bulky, with solid and seamless feeling.