Make no mistake about it, Yamaha isn't one of those companies that develops an off-road bike, gives it a lukewarm update the second year and then forgets about it to concentrate on the motocross side of the house. The tuning-fork engineers do spend a lot of time and energy on perfecting the YZs and YZ-Fs, but reading down the list of changes to the 2005 WR250F and WR450F shows they still care about their trail-oriented four-strokes. Sure, it might take a year for the trickle-across technology-such as the 48mm inner fork tubes-to arrive, but often the changes are concurrent, most notably the same-as-YZ revised intake tract and smoother combustion chamber surface.
The big news is Yamaha has finally addressed the WR line's chronic chubby feel. The new bikes are slimmer than ever before and carry their claimed 1-pound-lighter weight lower, thanks to a serious redesign that included lowering the engine cradle by raising the steering-head tube 10mm on the frame, shortening the shock 3mm and sacrificing a minor 10mm of travel. The 450 saw its seat height drop 20mm overall. These small adjustments equal big changes in the overall feel of the bike. But wait, there's more. The tank was also given a trimming, reducing the capacity a half gallon to 2.1 gallons, but it now shares the radiator shrouds with the YZ-F. Perhaps the biggest weight savings came from tossing the stainless steel ex-boat anchor, otherwise known as the silencer, for a svelte aluminum version that is both light and quiet. With the insert installed, the blue bikes whistle an 82-decibel tune; remove it and they both issue a still-muffled sub-96-decibel bark. Yes, we can now say quiet, performance and Yamaha in the same sentence!
WR450F
Overall, the engineers basically answered many of the gripes riders have had since the first WR400F: too heavy, too wide and too unruly in the woods. Besides the common changes to both WRs, the 450 had its carburetor and ignition settings revised to make more power and do it right now. To tame some of the big girl's notorious bite, the designers left the same piston in the bike after the chamber makeover, dropping the compression ratio to 12.5:1 from 12.3:1.
For those living in California, the big addition to the WR450F engine is an Air Induction System (AIS). Besides adding more tubes and hoses under your seat, the device routes clean air from the air-filter box to the exhaust port to lower the emissions. This means that for the first time ever, a WR-F is green sticker-legal. And Yamaha did it without stifling the output of the 449cc powerplant. That translates to just leave it alone; you'll be wasting time fiddling with bypass kits and all that. The only things we did before we attempted any serious riding was to replace the WR throttle-stop screw with one from a YZ450F (part No. 5JG-14591-00-00, $11.20), remove the 82-decibel insert in the exhaust and disconnect the famous gray wire under the tank.