Kawasaki has taken a subtle but very effective approach to improvements for the 2010 KX250F. Given the success of the green machine it’s a smart move; refining what has proven to be a lethal weapon on a motocross track. The KX’s 249cc, liquid-cooled, 4-stroke single-cylinder powerplant has received minor internal upgrades focused more on increasing durability than trying to boost power.
For starters the KX250F receives a “bridged-box bottom” piston, which gets its name from the reinforcing ribs that comprise the piston pin shaft. The new piston, with new crown design, is lighter and stronger with a shorter skirt and narrower piston pin to reduce mass, resulting in a quicker revving motor. The new exhaust pipe¬-made from stainless steel for increased durability-sports a longer head pipe married to a shorter mid-section to boost low-rpm performance. Pipe/muffler joint and clamp has been modified to improve exhaust seal while the tail of the muffler is rubber-mounted for shock absorption.
In the realm of the increased durability theme, wider oil pump rotors increase oil flow by 10% and a wider big-end rod bearing has been implemented. Also getting an increase in size is the KX’s radiators. The design of the fins is aimed at accumulating less mud. The new size results in overall added strength which allowed for the support stays to be removed.
Transmission received the bulk of internal rework with heftier dogs added to the 3rd and 4th input gears. The old circlip and washer design on the 4th input gear holding method has been eliminated with the 2nd input gear now carrying the weight load. The five-speed transmission has the same ratios as last year.
Chassis mods for 2010 are small, primarily with a smaller diameter steering stem and slightly less rigid swingarm. By reducing the rigidity the bike acquires a slightly lighter feel in handling. Seat height is 37.6 inches. Wheelbase is 57.9-inches. Ground clearance is 13.4-inches and the claimed curb weight is 231.4 pounds.
16-way compression and rebound damping adjustment Showa twin-chamber forks (with friction-reducing Titanium-coating lower) provide 12.4-inches of travel. Showa rear shock (fully adjustable) with the new rocker arm delivers 12.2-inches of rear wheel travel. Black triple clamps paired with black alumite-coated wheels give the KX a mean aura.
Test rider Parker Jones flogged the Kawasaki around the private Castillo Ranch Motocross track. Castillo Ranch is a perfect test facility, employing a mix of off-cambers, sand, hard-pack, uphills, downhills and a serious whoop section.
The KX’s power comes on strong through the entire pull of the throttle. The Kawasaki is carbureted as opposed to fuel-injected yet manages to deliver its power with linear, thoroughly predictable rush. The KX tracks superbly, getting its abundant power to the ground with surprising stability. The bike works as either a berm-railer or a point and shoot machine, allowing the rider to choose lines and adjust to changing track conditions with confidence. Front brake was slightly grabby but easily acclimated to. Gear shifts are positive whether on the gas and with or without the clutch.
The techs at Kawasaki know they have a potent machine in the KX250F and decided, quite rightly, to not mess with a winning package and concentrate on refinements that take the bike just that much closer to perfect. The added durability issue will pay off over the course of several seasons of riding and/or racing.
The 2010 racing season isn’t that far off. Look to Kawasaki to be putting the green machine at the front of the lites class, where it seems to be most comfortable.