Kawasaki: More power and changes expected to bring more popularity to the already popular green machines

Ron Lieback
AllAboutBikes.com Content Editor/Staff Writer

There’s no doubt about it: more power on the dirt equals fun and faster track times. A leader in the Motocross market, Kawasaki stuck with this power philosophy for their 2010 Motocross bikes, including the KX450F and KX250F. The newest bikes from Team Green have a host of minor changes, and, of course, more power.

Rumors were roosting about fuel injection on the 250F, but due to tight budgets in such trying times, carburetors are standard, unlike the fuel-injected 450F. The economy may have got the best of the 250F on the fuel-delivery side, but this doesn’t mean low performance. Since the 250F, and 450F alike, was an all-new model in 2009, the platform was already perfect for the upgrades for next year.

The upgrades to the 450F grabbing attention are revised bridged-bottom pistons, which are claimed to boost power up top and on over-rev. This design, along with reinforcements to the cylinder sleeve and right-side crankcase, is claimed to pro-long durability. Fuel-injection is now Digital (Digital Fuel Injection), giving more accurate fueling; the system works without battery power to keep weight low, and the ECU is adjustable, able to remember six hours of riding data.

Additional changes are cam-timing and ECU tweaks, which claim to raise low and mid to high rpm power. And to balance out the new engine, a refined intake cam advances valve timing by two degrees. The exhaust side of the machine is revised with a 40mm shorter header, a change from titanium to stainless steel for durability (and savings!), a larger-volume silencer with a claimed rate at 99 db, and a modified rear-muffler mount with a rubber damping collar.

The clutch has a lighter pressure plate, friction plates with 75 percent more friction material and better oil drainage. All together these changes claim to improve longevity and rider feeling. The chain was reduced to save some weight, and the radiators have tighter fins and tubs for strength and resistance to off-road build-up. And the chassis also is tweaked for upgraded suspension changes.

Lastly, easy starting is Kawasaki’s big kick for the 450F; the beast should start within three rotations of the crankshaft.

The motor on the 250F also received the revised bridge-bottom pistons, creating a lighter and stronger piston with a shorter skirt and piston pin. But the 250F piston features a modified crown to improve combustion. The height of cylinder was also raised, giving a 13.2.:1 compression ratio. The new crankcases are thicker, with more material around the engine-mount holes for durability. On the exhaust side, unlike the 450F, the 250F received a longer header pipe and shorter mid-section. The exhaust pipe is also stainless steel for durability.

The suspension was upgraded just as the 450F, but instead of Kayaba components, the 250F uses Showa. Cosmetically, the 250F has a thicker fender and is accentuated with weight-shedding black wheels.

As for the KX85, the mechanics remain similar to last year. But it’s donning some new attire: a black frame and wheels, black shrouds, lime green body panels and graphics that bring about a bold look.

Now it’s up to the consumer to see if the ’10 green machines remain a leader off the road.

June 24, 2009