For 2009, Kawasaki considerably improved its 4-stroke motocross lineup. The KX450F now uses fuel injection while the KX250F delivers greater performance at high engine speeds. Both models also benefit from weight-saving and chassis-strengthening features.

The KX250F delivers greater performance at high engine speeds.

KX450F
Specifically designed for a motocross, the new electronic fuel injection system of the KX450F incorporates a small, lightweight ECU that operates without a battery. To help cope with the shocks and vibrations of motocross riding, the fuel pump relay is integrated to the ECU.

Using only electricity generated by the kick starter, the engine of the KX450F can be started with only four rotations of the crankshaft. The system delivers electricity in the following order: 1) ECU, 2) fuel pump, 3) injector, 4) engine. The 43-mm throttle body makes use of a progressive throttle link to deliver sharper response and a quicker throttle body opening after the 3/8 open position.

This feature delivers airflow in much the same way as would an old FCR carburetor (with the same sharp control over power delivery) while offering the benefits of fuel injection on top of that (easier cold starts, no choke, higher fuel economy, reliability and regularity of the settings, etc.) The newly-designed fuel pump, located in the fuel tank, features a rubber fuel filter cover that wraps around the inlet port and acts as a fuel trap to ensure a stable fuel supply during vigorous motocross riding.

An optional user setting tool allows racers to reprogram the ECU's data maps for volume of fuel injected and ignition timing. This is an actual rewriting of the data maps to adjust engine characteristics to suit rider preferences. The tool can also be used as a data logger, recording up to six hours of data (engine rpm, angle of throttle opening, air-fuel mixture, etc).

2009 Kawasaki KX 450 F