AUG 27–2003 YAMAHA YZ450F–SPECIAL TEST
AUG 27–2003 YAMAHA YZ450F–SPECIAL TEST |
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All-new, faster than ever, but still a YZF The Dirt Bike Staff just returned from the infamous Lake Whitney motocross track in Whitney Texas for the press introduction of the new 2003 Yamaha YZ450F. This machine has been eagerly awaited by all enthusiast four stroke pilots and is Yamaha’s answer to onslaught that Honda has created since the introduction of their CRF450. It’s interesting especially since Yamaha virtually created the 4-stroke class when their YZ400 debuted in 1998. But in one short year, the sea of blue was painted over with red, and Honda’s lighter, easier to start CRF450 pretty much stifled the roar of the YZ. The goals for the new Yamaha YZ450F were simple. It had to be faster, lighter and easier to start. And really that’s no easy chore especially when we heard from Yamaha’s Mark Porter about the how long, involved and painstaking the testing was. Simply carving off the weight took mastery and every item on the YZ450F has received close and careful scrutiny. From the plastic, the fuel tank size, the engine hangers, the hardware, all internal motor parts, the brakes; each and every piece was studied and designed to work better and be lighter than their past efforts. Cracking the throttle yields an instantaneous leap forward, as the revised crank has some 20% less inertia. Indeed, every reciprocating part has been downsized and lightened, and racing technology has trickled down from Ferry’s works bike to the showroom floor. The ignition coil is integrated in the sparkplug lead and cap, and the tranny is a four-speed, which Ferry uses outdoors. Yamaha’s testing revealed that the four-speed 450F, with the stock 14/48 gearing has the same top-end speed as a ’02 426 with the preferred one-tooth lower 50T rear chainwheel. We don’t know about that, but the 450 does pull each gear longer than the 426, so much that we could circulate the Whitney track in third gear and even fourth. However, the high-compression (12.5:1 vs. the CRF’s 11.5:1) motor has much more compression braking, and we stalled it a few times when chopping the throttle over jumps. Also, the four-speed is going to limit versatility for off-roaders and dirttrackers. Overall, the new 450F is a darned effective motor with super-easy and consistent starting, near-perfect jetting, smooth shifting, gobs of linear power and almost-two-stroke throttle response, even though the muffler’s can has been extended 50mm and the Ti endpipe lengthened by 20mm. TUNING-FORK PEOPLE’S TUNE Whitney has red sand-loam soil with a few hardpacked sections, and the 450F suspension works very well on both extremes. It has the hooked-up feel of the 426 at both ends with excellent balance, and the action at either end is spikeless. The 46mm Kayaba fork still has some harshness on slapper landings on hardpacked jumps, but we tuned most of it out by going in one click on compression and out two on rebound. This results in excellent bottoming resistance and a bit freer front end for diving into turns. Lighter riders are happy with stock shock settings, but bigger pilots like Lumpster and Wolfster will need to crank in shock rebound to offset all the preload dialed into the spring. We went in two clicks and left high-speed and low-speed compression alone. The shock makes the rear-end feel planted, even on over-watered parts of the track. It’ll pick up stutter bumps without upsetting the chassis (Remember Yama-hop? It’s history), stroke smoothly into the meat of the valving, then bottom unnoticeably, if at all. Good stuff. 250F-HANDLING WITH 450 POWER The 250F-sized motor has very little gyroscopic effect, so it can be easily flicked into turns or whipped over jumps. Excellent throttle response helps bend it around corners and bury the backmarkers after the apex. A neutral handler, the 450F can be steered with the handlebars or with the throttle and brakes. It feels super-stable on rough sweepers, just like the 400 and 426. We’d dare say it feels like a punched-out 250F on ethanol and nitrous. For the sandy bottomlands at Whitney, one might want to drop the fork to be flush with the new top tripleclamp. This stops any tendency to knife in the soft, deep stuff. On tighter tracks, raise the fork for carving up RM250s and such. Also, the pilot’s compartment is still cramped in typical Yamaha fashion. The tripleclamps have solid bar risers that don’t allow fore-aft adjustments for rider size and preference. The low seat and high pegs cramp the legs of taller folk, too. But worse yet, the gas capacity dropped a whole liter, from 2.1 gallons to 1.85. Off-roaders won’t stray far from the truck with the stock tank for fear of pushing back. YZ450F YIPPIES!
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