Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/126340
I' III • ~ E Trans-AmA Bike Impression milkey Boone's·works HH25D Hawasakj: By Jim Gianatsis Photos by Chuck Tannlund and Gianatsis Kawasaki has a somewhat sneaky inclination to label their factory works 'bikes with the same nomenclature as their limited production motocrossers. Both are labeled KX, and . in the case of this week's TransAMA test bike it's the factory . k KX250 of MIC ey. Boone we got to put through Its paces. To avoid confusion with the production bike thou~h, it might be a good idea to label Mickey's Kawasaki as the KX250-78 R2. Thus to show the bike is a works. racer (the R) built .in 1~78 (the 7~) WIth the.number 2 designation me,!,rnng . t~e ~Ike .ha~ underg~>ne a maJo.r ~Ion ~tnce .Itsintroduction on the CIrcUIt earlier this season . The bike is nearly identical to the works Kawasaki ridden by Torlief Hansen with much success in the 250cc 24 World Championship this past season . The RI model. as you may remember, was first seen by us here in America at the beginning of the year in the Supercross Series where it was used by all of Team Kawasaki, and also by the "J ammer", Jimmy We inert In th e 250cc Na tionals. F~r a works bike the RI was perhaps a little cluttered, but well engineered and hand crafted with masterful workmanship. It was also inovative, with goodies like its ElectroFusion cylinder bore and the cam ad juster chain tens ioner for the rear axle . ' Where the R2 now differs from the earlier RI is in the rear suspension, with the R2 having its swingarm and frame modified so the works Kayaba gas/ oil reservior rear shocks are placed at a more vertical angle than before. This new angle seems close to 45 degrees with the swingarm positioned parallel to ' the ground , while the earl ier RI had its shocks at a much more radical 60 degrees laydown position. This change was needed because the more extreme laydown shock angle provides a decreasing rate rear suspe nsion as travel is used up , meaning damp ing action and spring rates become less. This is hardly wha t we need: a suspension which is stiffer on initial travel for smaller bumps and then softer for larger bumps. By placing the shocks in a more con ventional 45 degree position in the R2 design, the damping shaft and spring compression travel of the shock absorber units stay closer to a constant ra te of travel for a steady input of force (compression). Once we've accomplished this , it becomes much easier to tune the shock assembly for the increasing rate suspension we need as travel is used up, by employing progressive rate spri ngs and damping. The front suspension on the KX250 -78 R2 cons ists of good functioning Kawasaki specification Kayaba works air/spring front forks. Travel is equally balanced at both wheels with 300mm (11.73 inches) of usuable operating range. The factory bike uses lots of exotic metals, like magnesium for the hubs, drill ed titanium bolts for the en~ne mounts , and aluminum for the sWingarm and fork triple clamps. The tank is fiberglass and the fenders and other frame panels are lightweight plastic. This brings the weight down to a very competitive 203 pounds. The powerplant in Mickey'S bike was quite similar. if not identical. to a production KX -250 engine, rig lit down to the aluminum main cases and the five-speed gearbox. Actual displacement is 249cc , fed by a 38mm Mikuni carburetor through a six petal Boyesen reed valve. The only thing about the engine which 1 was unable: to confirm as to its being on the 1979 production model was the Electro?" Fusion cylinder and its porting. Some': what similar to the works Yamaha's chrome plated aluminum cylinders in reducing weight and im proving heat dissipation , Kawasaki's Elect ro-Fusion process uses high voltage to spray ant.. iron coating onto the bore of the aluminum cylinder. Other niceties on Mickey's works R2 include the full-floating rear brak and the well padded saddle, whicn merges smoothly with the very short gas tank to aid in sliding your weiglit forward in turns. The foot pegs a~~ also placed high to prevent dragging in deep berms. , II After check ing with Kawasak i's:! Steve Johnson for permission to tak e Mickey's bike ou t for a few hot laps after the Buchanan Trans·AMA rac e, and under the watchful eye of Mickey's" tuner/father, we pushed the KX-250 78 R2 over to a mound of dirt where we could gain a high enough height to mount the bike and ligh t off the.