Kawasaki unveiled its 2004 Motocross lineup today, showing off their new KX250F four-stroke (shared with Suzuki) along with aggressively revised 125 and 250 two-strokes.
The KX125 and KX250 motors have both been updated for '04 with reshaped combustion chambers, higher compression, and redesigned power valve systems, along with other changes designed to increase power and rideability. Both two-stroke KX's feature a new UNI-TRAK rear suspension linkage, which Kawasaki says "is anchored on the swingarm, drastically reducing front-to-back movement of the shock, resulting in smoother, more stable action and improving traction at the rear wheel when accelerating". Both bikes also feature 20mm longer swingarms, designed to absorb more suspension loads, allowing a lighter frame construction. Claimed dry weight is 191.2 lbs for the KX125 and 213.8 lbs for the KX250
If you read yesterday's article on the '04 Suzuki MX lineup, you already know some basic information about the KX250F/RM-Z250 four stroke. Briefly, The motor uses a dual overhead cam design featuring titanium valves on both the intake and exhaust sides. The motor's 77mm bore and 53.6mm stroke exactly match the specs of Yamaha's current YZ250F. Lubrication is via a "semi-dry-sump" system, with the transmission being used as the oil sump while the crankshaft spins in a separate chamber. The crankcase construction is described as "thin-wall", and the valve cover as well as both side covers (clutch and ignition) are magnesium to save weight.
The KX250F is also equipped with a two-stage ignition system: in neutral, the bike idles at a comfortably low rpm, but once in gear, the idle is raised to reduce engine braking.
The frame is a traditional twin-spar type, featuring D-shaped upper spars to keep the bike slim. The four-stroke 250 uses Kayaba suspension front and rear, and the rear suspension linkage features the same UNI-TRAK system as it's two-stroke brothers. Neither Kawasaki nor Suzuki has announced a claimed dry weight for their new four-stroke 250, but expect it to at least be competitive with the 208 lbs Yamaha claims for it's 2003 YZ250F.
We should get a chance to test the two-stroke KXs soon, and we hope to ride a KX250F or RM-Z250 within the next few months.
