Racing expert Kawasaki adds a new member to its unparalleled family of motocross bikes, namely the 2011 KX250F. While engineers concentrated more on the fuel-injected KX450F in recent years, the neglected one still managed to pile up victories in AMA Motocross and Supercross races in 2010.

Times are changing, though, and the little KX250F has received major upgrades for the new model year. Here's all you need to know.

Racing expert Kawasaki adds a new member to its unparalleled family of motocross bikes, namely the 2011 KX250F. (Photo: Kawasaki)

New fuel-injected engine
Lighter and smaller, the liquid-cooled single-cylinder naturally retains the most successful attributes of its predecessor, including a steady, generous torque curve. Key additions led by electronic fuel injection boost torque across a greater part of the daily rpm range, reducing the need to shift and allowing riders to focus more on their rivals.

Specially designed for motocross use, the battery-less injection system uses electricity generated by the kick starter. The engine can be started with only three rotations of the crankshaft. The system delivers electricity in the following order: 1) ECU, 2) fuel pump, 3) injector. With a warm engine, starting can be accomplished in a single kick.

A 43-mm throttle body makes use of a progressive throttle link for smooth power delivery at lower revs and more explosive delivery beyond that. The lightweight throttle body is approximately half the weight of a FCR carburettor – a weight saving of about 600 grams. Moreover, the high-rpm engine’s injector features four larger holes that increase fuel flow by about 20 percent over the KX450F.

The single-cylinder powerplant also benefits from a number of changes aimed at improving efficiency and reliability, including a shorter-skirt piston, a longer spark plug that protrudes 1.4 mm deeper into the combustion chamber and increased valve lift (from 8.7 to 9.3 mm).

The single-cylinder powerplant also benefits from a number of changes aimed at improving efficiency and reliability. (Photo: Kawasaki)