In the late 1960s, Kawasaki was continuing on a similar path as Honda with their CB 750, but they learned to their dismay in 1968 that Honda was much further ahead in the process. Instead of pressing on, Kawasaki went back to the drawing board and build a larger bike for the 1,000 cc class.
Honda’s SOHC 4-cylinder CB 750 was of course a resounding success with 440,000 examples sold over the next eight years, but the Kawasaki was a different sort of motorcycle. The engine was a 903 cc DOHC cross-frame 4-cylinder, and production began in 1972. The new Z1 redefined the term “runaway success” as nothing could keep up with it for several years, and it was voted Motor Cycle News bike of the year from 1973-76. The Z1 was also famous as the world’s fastest production motorcycle, the first bike in two decades to take the title from the old Vincent Black Shadow.
The Z1 was the most powerful Japanese bike built to that date with 82 bhp at 8,500 rpm – 15 more than Honda’s CB 750 – and could do the quarter mile in 12.5 seconds at 110 mph on its way to a top speed of 130 mph. The Z1 weighed 539 lbs and sold for $1,895. It was available with both kick start and electric start, and more than 80,000 would be sold in the first two years.
The engine’s power delivery was smooth and the bike seemed unbreakable, so the Z1 was quickly entered into competition. It remained largely unchanged until 1975, when the 903 cc Z1-B was introduced. Changes included increased horsepower, improved front forks, a stiffer frame with gussets at the steering head, and the automatic chain oiler was deleted. New paint colors were introduced, but the ducktail rear remained.
The Z1 was superseded by the KZ900 in 1976, when the bike gained a second front disc brake. Carburetors were reduced from 28 mm to 26 mm, but the air box was less restrictive and resulted in a net gain in power. A touring LTD model was also added with a cutaway seat, a third disc brake and a new exhaust system. The Z1000 then replaced the KZ900 the following year, followed by the café racer Z1-R and shaft drive Z1000ST tourer. In 1983, Kawasaki again took the title of fastest production bike with the GPZ 900R, which referenced the success of the earlier model.
A handful like-new preserved Z1s do exist in private collections, but quite a few of them were crashed or just ridden long and hard. The best bet in finding one is probably a dusty example at the back of a long-term owner’s garage and then bring it back to life.