2009 Kawasaki KX450F - Meaner And Greener

By Brian Catterson, Photography by Mark Kariya

For 2009, Kawasaki becomes the third Japanese manufacturer to offer a fuel-injected open-class motocrosser. The all-new KX450F uses essentially the same Keihin EFI system as the Honda CRF450R and Suzuki RM-Z450, with a 43mm throttle body, 12-hole injector and progressive, two-shaft throttle link that gives quicker response beyond 3/8-turn. Like the CRF, the KX gets by with a plastic gas tank instead of metal as on the RM-Z. Naturally with EFI, jetting changes are a thing of the past. Moreover, with no float bowl there are no worries of fuel sloshing causing bogging; and with no breather hoses no gas spills out, which is good for fuel economy and the environment. An optional setting "tool" with a diagnostic port bolts behind the front numberplate to allow further EFI tuning and data acquisition via a laptop computer.

Engine changes are comprehensive, with revised cylinder head porting, a 5mm lower head height and a new high-compression piston (12.5:1, up from 12:1) boosting power. A larger, heavier ACG rotor supplies the EFI system with the required electrical power while increasing inertia for smoother acceleration. A lighter, reshaped crankshaft offsets that weight increase while retaining the same balance factor. A revised automatic compression release with more lift eases starting. And new intake valve material, longer big-end rod bearing and a revised-angle under-piston oil jet improve longevity.

The aluminum frame has also been redrawn, with a slimmer head pipe, differently shaped spars, a larger diameter aluminum subframe and a "Tapered D" swingarm that pivots 3mm higher in the frame for improved stability and rear-tire traction. The chassis weighs 1.8 lbs. less than last year, working with a new one-piece titanium exhaust to offset the additional weight of the EFI system. The new, larger-volume muffler is said to be quieter but still chimes in at a too-loud 99 decibels. Less sound equals more ground-right, guys?

The suspension didn't escape the engineers' attention either, the Kayaba Air-Oil-Separate fork receiving Diamond-Like and Kashima coatings for reduced stiction. A more rigid upper triple clamp matches less rigid stanchion tubes for optimum flex, while 1mm less offset enhances front-tire traction. The reshaped Kayaba shock also gets a Kashima coating on its internals, as well as a 4mm larger piston. Mounting the Uni-Trak linkage below the swingarm allows a longer rear-suspension stroke for more precise control.

Just one week after we rode the '09 Honda at Lake Whitney, Texas, Kawasaki invited us to sample the '09 KX at Muddy Creek, a fun and jumpy track in Tennessee. Unlike the mold-breaking Honda, the Kawi feels like basically the same bike as last year, only better in every way. The first things you notice are the slimmer bodywork and seat, plus the lighter overall feel. The batteryless ignition requires three crank rotations to power up the system, but once charged the motor consistently fires on the first kick. That's a big improvement from the days when stalling meant certain defeat.

Power delivery is also much like last year, though noticeably smoother, which we appreciated when the hard-packed track surface dried out. Throttle response and clutch feel are very precise, and the low-end snap makes it easy to loft the front wheel over whoops or find the speed to clear jumps coming out of turns

Handling feels much like last year's model too, and steered better after the fork tubes were pulled up 3mm through the triple-clamps. Overall the bike is stable yet flickable, and the suspension proved plush yet resistant to bottoming. The brakes are powerful yet predictable, though the rear was somewhat easy to lock on the slick surface.

Kawasaki has worked magic with its latest KX450F, keeping what worked well while making noticeable improvements and adding EFI. We can't definitively say it's the best motocross bike of 2009, but it's certainly in the running.

By Brian Catterson
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