Kawasaki kept the motor about the same as last year. It still has the short DOHC cylinder head with a 12.5:1 compression ratio. Also retained from last year’s motor was the wedge-shaped crank that offsets 60 percent of the crankshaft’s reciprocating weight and produces an effective balance to keep vibrations down. The digital fuel injection (DFI) automatically adjusts to altitude and climate conditions via a small engine-control module, and a lightweight aluminum fuel pump is mounted in a different location in the fuel tank. Connecting the tuning software is now easier with a USB cable under the seat/gas-tank area.Kawasaki's 449cc Single does not disappoint in the power department.Like last year’s bike, Kawasaki suggests a leak-down test be done after ten hours of hard riding. All that horsepower needs to be maintained. We spoke with a rider at the press intro who campaigned a 2010 KX450F last season, and he relayed that even after 18 hours on the motor, the top end was still tight, and he only had to adjust the valves once. Good news for the Kawasaki four-stroke crowd.A 43mm throttle body holds an ultra-fine atomizing injector, set at a 45-degree angle for good midrange and top-end power, via a 12-hole system that sprays the fuel in at 60-micron particles, allowing for smooth and accurate power delivery throughout the rev range.Kawasaki also improved the transmission by incorporating a larger internal roller on the shift cam, and a stronger shift-return spring for more positive shifts, something our tester complained about on last year’s model.
Kawi also dialed in more flex in the aluminum chassis by incorporating steel versus aluminum mounting brackets for the motor. The piston crown has been redesigned to go with the larger high-volume muffler, along with a longer and hotter spark from the programmable ECU.Suspension has been modified to provide a supple ride over braking bumps, with damping settings matched to provide a smooth works-like ride for the aggressive rider. The 2011 KX has a D-shaped aluminum swingarm that features a cross section of narrow ribs and thin-wall construction. It pivots high in the frame to increase rear-wheel hook-up. Mounting the rocker-arm of the Uni-Trak rear suspension linkage below the swingarm pivot provides a longer rear suspension stroke and allows for easier shock tuning.
Keeping current on the latest technology, the fork received the slippery DLC (Diamond-Like Carbon) treatment to the outer surfaces of the inner fork tube. This minimizes stiction when the fork is exposed to side loads that would otherwise restrict the action. The suspension is very smooth due to a friction-reducing treatment Kawasaki calls “the Kashima Coat Treatment” on the inside of the forks tubes where all that damping and spring stuff is bouncing around. Also, the fork is a Kayaba Air-Oil-Separate unit that reduces frothing of the fork oil, which makes the fork handle rutted corners without pounding the rider’s forearms, a minor niggle on last year’s big KX. The rear shock wasn’t ignored and also gets the Kashima treatment with a larger 50mm piston, and more accessible high- and low-speed compression adjuster knobs. The shock also got a revised damping and spring rate to allow for a plush feel throughout the changes in track conditions.
The KX sports a narrow mid-section on top, with a firm urethane foam saddle with a non-slip surface to provide grip when standing. The KX gets wider at the bottom of the frame to provide the rider with better control. The 50mm-wide pegs offer superb grip and give the pilot a comfortable platform to work from.
