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.

In total there were a 186 changes done to the last 426 to make it a 450, most had gone into making the revolutionary thumper some 13 pounds lighter and infinitely easier to start without losing that famous YZF handling and bark. We’ll have to see how the 450F compares to the CRF in the shootout and on tracks across America, from Peoria to Washougal, but rest assured, the ocean won’t be all red anymore.

In gaining 23cc, the 450F was stroked 3.3mm, but why did it feel like a 250F the first time we slung a leg over it? Because the engine has been downsized and actually fitted with the kickstarter from the 250F. The new auto-decompression system on the exhaust cam makes starting as easy as the two-stroke YZ250. The downsized head, new frame and almost flat seat-tank junction exaggerate the 250F feeling, that is, until you snick it in gear and dump the clutch. Where the 250F wants first gear only, the 450F will happily launch in second or third, it has that much torque and off-the-bottom throttle response.

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.

Big news from the suspension front involves more tunability than ever and a new swingarm. Yamaha worked long and hard on lightening the components and reshaping the upper fork tube to work with the lighter, lower frame. Even the steering stem taper was massaged to provide flex were it’s most needed New Valving, although the owner’s manual now has fork preload adjustment by adding or removing 2.3mm washers under the rubber-bumper fork cap. Spring rates are 0.46Kg/mm fork and 5.3Kg/mm shock.

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.

As we’ve said many times, anyone can make a slow bike handle, the trick is to make a beast motor tame with the right combination of rigidity (tortional, etc.), flex, geometry, weight bias, and power delivery. We don’t pretend to know squat about any of those things, because we’ve never even owned a pocket protector, much less an engineering degree. We do, however, know a good-handling bike when we ride one, and this is one of the best ever. The suspension keeps each wheel on the ground, and the chassis flexes or doesn’t where and when it’s supposed to.

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.

Yamaha lowered and flattened the new gastank and seat, giving a very flat and narrow cockpit and plenty of fore-aft movement. This is good. However, the seat is incredibly thin, and the base actually drops in the center into the airbox area. Sitting over any G-outs flexes the flimsy base and puts your softer anatomy in collision with hard aluminum. Wolf hated the new seat and immediately called Guts for a taller one. Too bad the 426 seat won’t fit the 450F.

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.

* Yamaha’s rear master cylinder with integral reservoir is downsized some 11 percent from ’02, while Honda’s rear M/C is 32 percent smaller. Boil-overs shouldn’t be a problem with the 450F as it was with some CRF brake-draggers. Both YZF brakes are strong with good feel at the respective levers.
* Keihin’s flat-slide carb gets a new designation, FCR-MX, as the body no longer has the bolt-on intake bell, and the cable cover is aluminum. Where the KTM 525 went to 41mm, the 450F stays with 39mm.
* We never crashed the 450F, so we didn’t feel the need for the bar-mounted hot-start lever. It’s sure nice to have the automatic decompression system built in like the CRF. You don’t even have to fish for neutral.
* Standard fork-oil level is 135mm, with an adjustment range of 80-150mm. The manual reminds us not to use more than two preload washers, so there’s only 4.6mm of adjustability there. On the other hand, Kawasaki removed the HSCD adjuster on its shocks, and Yamaha didn’t.
* Besides the non-adjustable, non-damped perch, the YZF still comes with cost-cutting, cheesy chain and handlebars. And, although the headpipe is completely Ti, including the heat shield, only the endpipe of the muffler is Ti, so the aftermarket pipe makers will have something to do this winter.

Yamaha kept all of the great traits of the 400/426 and improved on throttle response, suspension and handling, but the biggest news are the CRF-class weight and starting ease. We’ll have to see if the dirttrackers and supermoto guys jump off of the CRF bandwagon, but you can bet the local and national motocross tracks won’t be all red for ’03. The 450F is as light and flickable as the upstart Honda, so, from a distance, starts will look purple, maybe even bluish-purple. The question will likely be, is balance and a planted feel (YZF strengths) more important than a lack of four-stroke compression breaking (CRF)? Or will four speeds beat five?

* YZ250F flickability with 450 power
* Fall-on-the-lever starting drill
* Bar-mounted hot-start just in case
* Balanced, widely-adjustable suspension
* Planted, neutral-handling chassis
* Wide power, thin ergonomics

* Four-speed gearbox less versatile
* Non-adjustable, non-damped tripleclamps
* New seat foam too thin, base flexes
* Smaller tank cuts fuel range 12-15%
* Light flywheel enertia causes stalls
* No juice clutch, bulge bar, stout chain

FROM 426cc TO 450cc
* Stroke increased from 60.1mm to 63.4mm
* Four-speed tranny, all ratios higher
* New cases with less ‘pumping loss’
* Direct ignition like Ferry’s works bike
* Auto-decompression, bar-mounted hot-start
* Smaller head, Ti valves and headpipe
* New crank with 20% less enertia
* Smaller waterpump, camchain tensioner
* Ti endcap is 20mm longer, 50mm longer can
* New cush-drive for primary gear
* New frame rigidity, balance, 500cc less oil
* Reserviorless rear brake m/c, new caliper

* Temperature: 80-98 degrees
* Humidity: 40-60%
* Altitude: 640′ MSL
* Fuel: 91 octane pump
* Jetting: 165 main, 100 pilot-air, 42 pilot, NCVQ/4 needle, 2 out on airscrew
* Fork: 11c (12 std), 12r (10 std), std position (5mm above clamp)
* Shock: 12 LSCD, 1.5 HSCD, 10r (12 std), 100mm rider sag

2003 YAMAHA YZ450F
Engine type…DOHC, 5-valved, liquid-cooled 4-stroke
Bore and stroke…95.0mmx63.4mm
Carburetion…39mm FCR-MX Keihin/w TPS
Fuel tank capacity…1.8 gal. (7L)
Final gearing…14/48
Lighting coil…No
Spark arrester…No
EPA legal…No
Wet weight (no gas)…N/A
Wheelbase…58.5 in. (1485mm)
Rake/trail…27.2@/4.6 in.
Ground clearance…14.6 in. (371mm)
Seat height…39.2 in. (995mm)
Tire size and type:
Front…80/100-21 Dunlop D739FA
Rear…110/90-19 Dunlop D739
Front…KYB 46mm cartridge fork, adj. reb.,comp., 11.8 in. (300mm) travel
Rear…KYB aluminum piggyback, adj. prld., reb., hi-lo comp., 12.4 in. (315mm) travel
Country of origin…Japan
Suggested retail price…. $6,299
Yamaha Motor Corp.
6555 Katella Blvd.
Cypress, CA 90630
(714) 761-7300


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