Other visual changes to the '06 come from the trick-looking triple clamps, with available 111/48-inch mounts for an oversize bar, smoother hubs front and rear, petal-style front and rear disc brake rotors, a Renthal aluminum bar, new grips and four less spokes on the rear wheel. Yep, exactly four.
Now for the stuff you can feel at the wrist.Inside the engine Kawasaki revised the intake and exhaust ports as well as the combustion chamber to beef up the low to mid-rpm pull. It also concentrated on top-end boost by increasing the compression ratio from 12.6:1 to 13.5:1 specifically to improve high-rpm performance. Stiffer valve springs were included to help keep the valves opening and closing when the throttle is tapped, and a new surface-hardened crank is used for extra rigidity. To stand the torture of high-rpm output, the piston also gets thicker crown material and oil flow has been increased by nearly 20 percent thanks to more efficient oil pumps.
Even the intake is improved on the KX250F with a new airbox and intake boot shape vastly improving flow to the carb. About the only thing not touched is the pipe and muffler combo. It could literally be swapped with last year's because it's exactly the same (and just as loud, but more on that later. There's still more new stuff).
The power-transfer department gets some updates as well. New friction plate material and stiffer clutch springs improve the clutch feel, and heavier gear construction should keep the transmission in check with the more powerful engine.
So, finally, how does all this work? Well, quite honestly, it works great.
The '06 KX250F is a superb motocross machine that takes full advantage of its own improvements. Standing out the strongest has to be the new chassis with the motor and finish improvementsfollowing closely behind. Not once did the new suspension let down any of our testers. The bike tracks straight, eats up chop, soaks up landings and corners just as well as one of the best-turning bikes in the sport: the '06 Honda CRF450R. Showa components and aluminum perimeter frames are a great combination on two brands now.
Often new frame designs put manufacturers through a learning curve. We all know Honda had its issues at first, but one ride on this Kawasaki and you'll swear you have a fourth-generation Honda frame under you. The bike has rigidity where you need it and flexibility where you want it. It's an excellent chassis and a home run for Kawasaki on its first at bat. Ergonomically, the bike scores again. The frame is easy to grip with ankles or knees. And the bar to footpeg ratio is spot-on for the average-sized rider. The new grips are soft and tacky, allowing you to hang on with relaxed hands. But they did seem to wear a little quicker than others. Whether we were riding the exclusive Castillo Ranch Motocross Park with its loamy, deep soil or the fast laps of Perris Raceway with its rutted corners and jump combinations, this bike handled excellently.
Enginewise, the Kawasaki improves again. Although not nearly as impressive as the suspension and handling improvements, the new powerplant is substantial in the least. Plain and simple, the motor likes to be revved; the more you twist the throttle the happier it becomes. It has a very linear delivery with a high power level at all rpm that would rather work right here and now instead of screaming further into the higher revs. Typical of what we've come to expect from the Kawasaki four-strokes, this motor seemed tight to us. Also, when you shut the throttle off, the revs drop off quickly. With time this begins to loosen and allows the bike to rev and coast more freely. We got a bit more power by dropping to a 175 main jet, but this was during 90-degree weather.