Just two short years after it was introduced to American motocross racers, the championship-winning KX™250F motorcycle has been revamped – even though it already has five titles under its proverbial belt.
Numerous changes have been made to the potent KX250F. It produces significantly more power than the 2005 model it replaces, and like the new flagship KX450F, the KX250F sports an all-aluminum perimeter frame.
The 249cc, liquid-cooled, four-stroke engine now gives the KX250F a harder-hitting powerband, especially from mid- to high-rpm, and it extends that smooth, traction-grabbing power into the over-rev range.
Additional enhancements include revised intake and exhaust ports, and a revised combustion chamber for stronger low- to mid-rpm performance, while new cam profiles and a higher 13.5:1 compression ratio improve high-rpm performance. To compensate for the increased output, the piston now has a thicker crown.
Other engine modifications include stiffer valve springs to help ensure reliable valve control at high rpm; a surface-hardened crankshaft for additional rigidity; more efficient oil pumps that increase oil flow by nearly 20 percent; a new stick ignition coil that reduces overall weight; and newly designed, high-capacity Denso radiators that deliver superior cooling performance due to their more tightly packed cores and new fin design. Kawasaki also revised the timing and lift of the decompression system, so starting the KX250F is even easier.
The clutch and five-speed transmission have also been modified to include new friction plate material and stiffer clutch springs for improved clutch feel, and the gears have beefier dogs to match the more-powerful engine. Kawasaki engineers have also given the KX250F shift drum a new cam to improve shifting feel.
The most visible change to the KX250F is the aluminum perimeter frame. As with the KX450F, Kawasaki engineers combined their experience designing steel perimeter KX frames and techniques used to construct the Ninja® ZX™-10R sport bike chassis to create an all-new aluminum perimeter frame. Comprised of forged, extruded and cast aluminum parts, the strong but light design gives the KX250F the best possible balance of torsional and longitudinal rigidity necessary for superior handling characteristics.
The frame was designed so that the center of gravity and key chassis dimensions would work together to enhance the rear tire’s ability to drive the KX250F forward instead of squatting under acceleration. Additionally, the four-stroke engine sits in an upright position within the new frame to further aid overall traction.
The slim profile of the KX250F frame, two-piece radiator shrouds that leave the upper frame spars exposed, and careful design of the remaining bodywork make the KX250F feel light and narrow beneath the rider.
The KX250F’s high-performance suspension has been designed to complement the new frame. Up front, a Showa twin-chamber fork keeps the oil and air in separate chambers for consistent damping performance during long motos. On the rear, a new UNI-TRAK® rear suspension system, featuring an alloy swingarm with tapered spars and revised linkage ratios maximizes traction under acceleration.
Front and rear petal disc brakes provide stopping power for the KX250F. This design not only helps to reduce unsprung weight, but the petal shape of the discs helps to clean the brake pads for more efficient braking performance.
In addition to aggressive new bodywork and a new seat, the KX250F comes with a Renthal aluminum handlebar and an aluminum skid plate as standard.
To minimize overall weight, the KX250F utilizes aluminum instead of steel for several components, including the clutch cable elbow, clutch cable fitting nuts, fuel tank fitting nuts, seat mounting brackets, front brake hose clamp and igniter stay bracket. Kawasaki engineers also eliminated the upper mounting brackets of previous designs for the plastic fork protectors.
Optional parts for the KX250F include magneto rotors with different inertias, a 12-tooth countershaft sprocket, top mounting clamp for an oversized handlebar, aluminum and steel rear sprockets, solid petal brake rotors for wet races, different springs for the front fork and rear shock, manual decompression lever and cable, and a 20-inch front wheel.
Those who race their KX250F at designated events are eligible to receive support from Team Green™, Kawasaki’s amateur racing support program. Each year, Team Green provides regional support vehicles and highly trained technicians at more than 100 events, offering technical information and assistance to those who race Kawasaki products. Kawasaki also offers a comprehensive contingency program for amateur and professional riders who place well at designated events.