The Kawasaki Z1 may not be rare, but it is one of the most significant motorcycles ever, and an all-time classic.

As the Baby Boomers hit their sixties, they are redefining the parameters of collectable motorcycles. Not so long ago the staple classic bike was a 1960s British parallel twin, but as fewer motorcyclists remember the thrills of kick starting and oil leaks, the goalposts have now moved to the next decade. This decade really began in 1969, a pivotal year for motorcycling.

Honda released their landmark CB750 four and Kawasaki the potent Mach III triple (AKA “The Rocket with a Sprocket”). Britain tried their best with the Triumph/BSA triple but this was merely a last ditch stand before eventual obliteration. For Kawasaki, the two-stroke Kawasaki Mach III set new performance standards, but provided limited comfort, was excessively thirsty, and outside the mainstream of motorcycle design.

Kawasaki 900 Z1

Even before the Mach III’s release Kawasaki was working on a new four-stroke 750 four. As far back as 1967 Kawasaki engineers had plans for a four-stroke super cruiser in the mould of the 1000 cc Vincent. Their plan was for a bike that would be easy to ride in any situation, offering unparalleled top gear performance. But when Honda unveiled their CB750 in October 1968 they were forced to take timeout for a rethink.

Rather than scrap their existing 750cc N600 project, Kawasaki decided to upstage Honda. They increased the displacement and included several features previously the reserve of exotic cars or racing motorcycles. The transverse four-cylinder four-stroke engine had square dimensions (66×66 mm bore and stroke) and displaced 903 cc.

Kawasaki 900 Z1

The engine tune was very mild, with an 8.5:1 compression ratio, 36 and 30mm valves, and four Mikuni VM28 mm carburettors. But features such as double overhead camshafts and a 9-piece pressed together roller bearing crankshaft set the Z1 apart from the competition. The crankshaft was supported by six main bearings, with one-piece con-rods.

The primary drive was by straight-cut gears, the drive cut directly into the flange of the number four crank counterweight. This resulted in a compact and direct primary drive system that minimised drive train snatch.

Although the pressed-up crankshaft was an expensive solution, it was incredibly strong, and when welded together could handle enormous power outputs.

Endeavouring to quell any criticism of low quality and cheapness that had blighted some earlier Japanese products, Japanese motorcycles of this era were seriously over engineered. But even compared to others the Z1 took robustness to a new level.

Kawasaki 900 Z1

Anticipating future environmental controls, sintered alloy exhaust valve seats allowed the use of lead-free fuel, and a positive crankcase ventilation system with an air/oil separator on top of the crankcase was incorporated above the gearbox.

With an environmentally quiet (84 decibel) four-muffler exhaust system, the power was 82 horsepower at 8,500 rpm. The Z1 was unquestionably the most powerful production motorcycle available when it was released at the end of 1972.

While the engine specification set a new standard for production motorcycles, the chassis was more conventional. Norton’s legendary Featherbed inspired the mild steel double cradle frame, while the unremarkable suspension included a 36mm Kayaba front fork and typical under damped Kayaba twin shock absorbers.

The braking was also marginal considering the power, but the 296mm stainless steel single front disc with floating caliper was state of the art for the day. With Dunlop K103 and K87 Mk II tyres, specifically designed for the Z1, handling was acceptable but not outstanding. The early 1970s was an era where engines dominated the chassis, particularly with Japanese bikes, and sometimes-loose handling was the norm.

Kawasaki 900 Z1

The dry weight was a considerable 230 kg, but nothing else at the time could match its engine performance. Period road tests posted standing 400 metre times in the low 12 seconds with terminal speeds of above 180 km/h, and a 210 km/h top speed. Considering all Z1s came with an upright riding position and a high, wide handlebar, this was impressive. And at Daytona in March 1973, three stock Z1s and a number of riders set forty-five speed and endurance records, immediately earning a reputation for speed and reliability.

This combination of performance with general ease of use, electric start and overall reliability, put an even larger nail in the coffin of British motorcycling than Honda had managed with the CB750. Distinguished by a black highlighted engine and “Jaffa” black and orange colours, thousands of Z1s were sold in 1973. Ordinary people, who just happened to like terribly fast motorcycles, rode them on the street.

Kawasaki 900 Z1

Kenny Blake That year rode a Z1 single handedly to win the Castrol Six-Hour production race, defeating the thirstier 750 H2 of Warren Willing and John Boote by 30 seconds. Production numbered more than 80,000 units during 1973 and 1974 and the Z1 was well on its way to becoming Kawasaki’s most successful model. Kawasaki couldn’t meet demand and with most destined for America Z1s were in short supply in Australia and Europe.

The Z1 became the similar Z1A in 1974, changes largely limited to colours and the natural alloy silver engine finish. For 1975 the Z1B lost the automatic chain oiler, the front forks received revised dampers and softer springs, and to improve low speed running the automatic ignition advance was revised. It was a downhill slide after that, the Z900 detuned for 1976 before the Z1000 replaced it for 1977.

Kawasaki 900 Z1

As with most collectable motorcycles the first model is generally the most desirable, and it is the same with the Z1. The 1973 series command the highest prices but if the kudos of owning the first model isn’t important the Z1A and Z1B are almost identical for a lot less investment.

Good looking, easy to live with, reliable, and offering performance that isn’t too shabby even by modern standards, it’s not surprising the Z1 has become the classic motorcycle of choice for the cashed-up Baby Boomer.

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Darky
Darky
10 months ago

A fabulous read, on arguably the greatest bike of all time….

Lloyd Jones
Lloyd Jones
Reply to  Darky
9 months ago

The 916 duke is up there as well ….