1976 Kawasaki KZ900
Claimed power: 82hp @ 8,500rpm
Top speed: 120mph (est.)
Engine: 903cc air-cooled DOHC transverse mounted inline four, 66mm x 66mm bore and stroke, 8.5:1 compression ratio
Weight (dry): 511lbs (232kg)
Fuel capacity: 4.7gal (17.8ltr)
Price then/now: $2,475/$2,000-$6,500

In 1976, Kawasaki was putting the final touches on its next big-bore challenger, the soon-to-be-released KZ1000. Until then, the top of the line was the KZ900, essentially a dressed up Z1, only better.

In the late 1960s Kawasaki was in the kitchen, cooking up what it dubbed their New York Steak project. They couldn’t have known, however, that their featured dish — a 4-stroke, 4-cylinder big-bore motorcycle — was about to be upstaged by the Honda CB750.

Starting in 1967 and working into 1968, Kawasaki was designing “a Super-cruiser, a machine to replace the legendary Vincent HRD of yesteryear.” At least, that’s how Ivan J. Wagar, writing in the October 1972 issue of Cycle World, described the unlikely code-named New York Steak project. Kawasaki’s research indicated the market was hungry for a reliable, large-capacity motorcycle capable of high performance that, when asked, could also be a decent touring machine.

Kawasaki engineers were well underway with a mocked-up machine equipped with a 750cc 4-stroke engine when Honda burst their bubble with the CB750. Work stopped on the project, but Kawasaki picked it up again in 1970 and decided to go ahead with its original plan, which was, Wagar wrote, a big bore bike with “good handling and brakes.” It was to be fast and comfortable “along with low noise and emissions as design criteria.” According to Wagar, Kawasaki engineers were still aiming for a 1972 production target.

Bigger and better

Although Kawasaki’s forte was mostly 2-stroke engine development, 4-stroke technology wasn’t new to the company. Kawasaki produced its first 4-stroke, a single-cylinder 148cc motorcycle engine, in 1953. Ten years later, in 1963, Kawasaki absorbed Meguro Works, Japan’s oldest motorcycle maker and manufacturer of a number of 4-stroke engines, and became the Kawasaki Motor Sales Co.

Ben Inamura, an engineer Kawasaki inherited with its acquisition of Meguro, was responsible for engine development. Contemporary press reports indicate he was simply instructed to build an engine “that works,” whatever the engine capacity. Honda’s introduction of the CB750 helped underscore the fact Kawasaki’s new 4-cylinder engine would have to be larger than 750cc. In this case, it was 903cc.

North American testing began in February 1972, and by mid-year Kawasaki finally delivered the code-named New York Steak as the Z1 900. The Z1 became a 1973 model-year machine, and when it was introduced it was the largest and most powerful 4-cylinder 4-stroke Japanese motorcycle ever built.

Inamura’s 903cc engine featured chain-driven twin overhead cams actuating shim-over-bucket valves. The head had shallow, hemispherical combustion chambers and the flat-top pistons gave a reasonable 8.5:1 compression ratio. With special sintered-alloy exhaust valve seats, the engine could run on lead-free gasoline. The Z1’s crank was pressed together and turned on roller bearings, while the connecting rods used caged needle bearings. Fuel and air mixed in a bank of four 28mm Mikuni carburetors. The finished engine produced a claimed 82 horsepower at 8,500rpm, delivered to the pavement through a gear primary drive turning a 5-speed gearbox and chain final drive.