2011 Kawasaki KX250F and KX450F Motocross Bikes - First Look

It should come as no surprise that Kawasaki joins Lites-class rivals Honda, Suzuki and KTM by adding fuel injection to its 2011 KX250F. After securing both the 2010 AMA East- and West-coast Lites Supercross titles with riders Christophe Pourcel and Jake Weimer at the helm of Monster Energy/Pro Circuit/Kawasaki-backed KXs, you would think that the Green machines were good enough. But staying at the top is hard business.

Starting with the headline-grabber: Kawasaki's Digital Fuel Injection system features the same 43mm, single-injector throttlebody and lightweight aluminum fuel pump as its big brother, the KX450F. Like on the 450, the system does not require a battery; the engine can be started within three rotations of the crankshaft using the energy generated by the initial kick to power the system. An optional ECU Setting Tool allows owners to select from several ECU maps or to be able to fine-tune a custom map for fuel and ignition to suit different conditions and rider preference.

Compression has been bumped up from 13.2 to 13.5:1 via a modified cylinder and changes to the Bridged-Box Bottom piston. A new intake camshaft provides more lift. Air-cleaner duct volume has been increased, while a longer exhaust header pipe helps produce more low-end and midrange power. A new exhaust silencer has more volume for reduced noise.

Engine changes aren't the only area where Kawasaki concentrated its efforts. The chassis receives significant updates, too. A new Separate Function Fork (SFF) differs from a conventional unit by separating the spring and damping tasks. The right leg contains the spring (the preload adjuster is atop the blue anodized cap), while the left leg incorporates the cartridge assembly and fork oil to manage compression and rebound damping. Additionally, the fork sliders feature a titanium-oxide coating which, combined with the rest of the new design, is said to reduce stiction and improve performance. The shock was revised to suit the new setup at the front.

An updated transmission, new bodywork and gripper seat round out the highlights.