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Kawasaki - Works Motocross Motorcycles

    A works motorcycle is a hand built, highly tuned, ultra light, cost is no object motorcycle, built at the factory, in limited numbers, for the top factory riders to compete on. Usually, these machines were destroyed at the end of a season, to ensure that the competition never got to see it up close. Despite this rule, some of these bikes have survived, and we won't get into how that may have occured, but thankfully, some still exist.
    Like all manufacturer's, Kawasaki produced a long line of works equipment which served many purposes. Works bikes are about as good an advertisement as a company could get. Imagine being a kid at a race in the 70's watching Jimmy Weinert or Gary Semics rip it up on a works SR250..the next thing that kid did was mow every lawn he could to buy the closest thing to that SR...a KX 250. Secondly, works bikes allowed the factory to test out different ideas, set ups, materials, or just about anything else you could imagine...some of which made it onto the next years production bike, which hopefully kept them ahead of the competition, leading to sales. Thirdly, everyone else was running some form of a works bike, so to be in the game, Kawasaki had to do the same. 
    Some of the things that made these bikes so special had to do with power to weight ratios, power curves, light weight materials, and suspension travel. Power to weight ratios is the act of building a machine that will produce the maximum useable power possible, by any means, in conjunction with the lightest possible chassis. The power curve refers to the way the engine excellerates from just off idle to the point of peak power, and how that power is delivered. Engines that produce a steady climb to peak with a tourquey feel were easier for the rider to control over an engine that hit peak really quickly . Light weight materials such as aluminum, titanium, magnesium, alloy magura, thin wall chrome moly, and plastic composites allowed for a very light rolling chassis to be constructed, because weight is the enemy of the racer. Finally suspension travel comes into play, and in the 1970's, it was one of the biggest battles fought by most factories. Everyone wanted more wheel travel, which allowed the bikes to jump higher and farther. It also was very necessary because the bikes were getting a lot faster, which meant the old designs wouldn't handle the speeds and stresses well. This also led to some major chassis design changes like diameter of tubing used in construction, placement of gussets, rake, trail, ect. All of these things played a big part in the evolution of production motocross machinery, but was first used on the works bikes. Below are many pictures of Kawasaki works motocross bikes, which for decades have carried the model code of SR. We start around 1973 and finish in 1979. Compare the first picture to the last one......a lot happened in six seasons at Kawasaki.

Notice the forks on this SR 400

SR400 with external fork springs

1976 SR-125

Semics on the 76 SR

1977 SR with liquid cooling
1977 SR with liquid cooling

SR 380

1979 SR with Unitrak and liquid cooling in Japan