Cycle News - Archive Issues - 1970's

Cycle News 1979 11 07

Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles

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! TBANS-USA BIKES TBA S-us E Four-Stroke Bad BradlleftlandJammin' Jimmy plan to be back in action on the Uni-Traks in Europe next year. Power ~And Q,) 1 Better ~ Suspension Rules The Roost Part. By Jim Gianatsis T his year's new Trans-USA MX Series has become a proving ground for new designs. Innovations and ideas which will tackle the World and National MX Championships during 1980 were being sorted out beforehand. And with suspension travel having reached its maximum limits around 300mm you may think new innovations are hard to come by, but on the contrary, now that the old molds have been broken, so to speak, the new technology of the sport has become even more progressive. Two major goals have been set by the factory teams engaged in the turf slinging wars. The first is to build more tractable and responsive powe~ bands for their 500cc class monsters. The second is to refine the performance of suspension components now that they have all that travel to play around with. Certainly the most exciting new bike which meets these goals is the variable leverage ratio rear suspension RC 500 from Honda. The other factory tearns have their own ideas how these goals should be met and it is the difference in execution to achieve these goals that hel ps to make the sport of motocross as exciting as it is. Kawasaki KX 420 Uni-Trak Most of the Kawasaki team members including Jimmy Weinert are riding pre-production modified versions of the 1980 Uni- Trak bikes. These feature 300mm of travel at each end provided by Kayaba air/spring forks up front and a Kayaba deCarbon reservoir coil-over Uni-Trak shock for the rear end. The new Uni-Trak rear suspension performs well, though it does make the bike more difficult to work on and fairly heavy for a works bike at 228 pounds. The factory bikes could be made lighter with the use of more titanium and magnesium parts, especially a titanium spring to replace the heavy steel Uni-Trak shock spring now being used. The pure production KX 420 will probably be 10 pounds heavier at least, close to 240 pounds, what with the use of a heavier KX 250 rear hub to replace the KX 125 hub now beinR used, along with steel bolts, heavier gauge steel production exhaust pipe, and probably a steel bodied Kayaba shock to replace the aluminum works shock. The engine is fairly old design from the production KX 400 motocrosser of a few years back as evidenced by the forward placed countershaft sprocket. The 420cc Electro-Fusion sprayed cylinder is similar to the one on this year's KDX enduro bike, fed by a 38mm Mikuni carburetor and sixpetal cylinder reed induction. That the engine's powerband is highly tractable is evidenced by the fact the fac-, tory bikes use a 4-speed gear cluster in the transmission to save weight, while the production bikes will have more versatile 5-speeds sandwiched in their aluminum cases. Despite its tractability and power, the 420cc motor is also pretty snappy and quick, so there is also a 440cc cylinder and piston assembly used by the team riders who want an even smoother power band with less kick and more grunt. Though visually similar to the preproduction KX 420s being used by other Team Kawasaki riders, Brad Lackey is riding an all-new KX 440 prqtotype which will serve as his GP bike for the 1980. Everything is different, from the frame and suspension which features a longer swingarm and huge 43mm Kayaba forks, to the engine cases which are smaller and lighter with a more rearward placed countershaft sprocket. One Kawasaki innovation found on all the team bikes is the unique cam adjustment rear axle. Unfortunately, this easy and accurate device for adjusting the drive chain will probably never see production because of its prohibitively expensive manufacturing cost and conventional chain pullers will be used on all production Uni- Trak bikes. Steve Stasiefski checks over Lackey's exotic 1980 KX-440 GP racer featuring smaller engine cases with more rearward located countershaft sprocket. I \ t 16

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