Kawasaki Kx450f

KAWASAKI KX450F

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COMPLACENCY MUST BE a taboo word around Kawasaki’s Akashi Works design facility in Japan. After all, just one model year after it rolled out the new 2009 KX450F-joining Suzuki and Honda in the fuel-injected MX big leagues-Team Green is back with a significantly updated 450.

No aspect of the $8049 KX450F was spared the designer’s stylus and CAD program in the revamp. Among the many engine changes, the new bridged-box-bottom piston (6mm shorter skirt, slipper-type) is claimed by Kawasaki to be the first of its kind used in a mass-production application. A new crankshaft has additional inertial mass to improve rear-wheel traction, while wedge-shaped chamfers on the edges of the counterweights improve balance for reduced vibration. These changes also necessitated a stronger cylinder for better piston durability.

Helping to optimize power output are a new intake camshaft and sprocket, which advance timing by 2 degrees. The digital fuel-injection settings in the ECU have been altered to provide more low-end and midrange power. “The engine is awesome,” said Off-Road Editor Ryan Dudek. “Bottom-end power is smooth and controllable, and the engine f pulls very hard through the midrange. Topend power tapers off early, but this is only noticeable on really long straights.”

Racers may want to purchase the optional ECU setting tool (part # 99999-0240, $515), which allows reprogramming of fuel and ignition maps in addition to acting as a data logger (records six hours). Contributing to the improved powerband is a new exhaust header, now 40mm shorter and made of stainless-steel in place of titanium for better durability. A larger-volume aluminum silencer is now rubbermounted. More power equals more heat, so thicker and wider radiators keep engine temps within an acceptable range. A new clutch design features 75 percent more friction material and improved oil drainage for better feel and longevity.

Although changes to the chassis aren’t as radical as those to the engine, there are plenty of them nonetheless. A new swingarm and linkage are mated to a Kayaba shock with revised spring rates and damping settings. Up front, the story is similar, with the Diamond-Like-Carbon coated, Air-Oil Separate Kayaba fork having received new spring/ damping settings.

Despite those changes, Dudek had some minor issues with the suspension. “I feel the KX is undersprung,” he said. “Although I am most likely lighter (163 pounds) than your average 450 buyer, I regularly bottomed the fork on jump landings.”

Handling performance varied depending on where on the track Dudek rode. “Entering corners with even moderate braking bumps, I couldn’t get the chassis to settle down, and it wanted to shake its head,” he said. “Lowering the fork in the triple-clamps to raise the front end, however, helped. In smoother corners, the bike steered very precisely and felt lighter than its claimed 250-pound curb weight would lead you to believe.” Overall, the KX is a very easy bike to adapt to, even after just a few laps on the track. As a Cycle World Ten Best Bikes Honorable Mention in 2009, the big KX came oh so close to a class victory; can these changes push it to the top? This may finally be the year we see green instead of red.

"Yearly updates are now the MX norm; somehow, Kawi has managed to make really good even better."

Blake Conner