Phantom bike introduction (1)

(Phantom bike) Kawasaki two-stroke monster, Square-Four 750 (Steak tartare)

Although there are many machines that don’t appear after being discontinued mid-development, it is rare that we ever get to take a proper look at what might have been. So we would like to pick up on some of these phantom bikes. This time we will introduce the Kawasaki Square-Four 750.    

Abandoned thanks to American exhaust emission regulations

In 1969 it was Kawasaki that aimed to have the fastest bike in the world with their two-stroke, straight three-cylinder, 500cc Mach 3, but standing in the way of this was the Honda CB750 Four that appeared around the same time. In order to defeat this, a two-stroke, three-cylinder 750cc Mach 4 was released in October 1971. This was announced as having a top speed of 203kph, and took back the world’s fastest bike title. In the autumn of the following year, a four-stroke, four-cylinder 900 Super Four (Z1) was also announced, and in a flash it was these two Kawasaki bikes that firmly took hold as the world’s fastest bikes. Also, in the backdrop of the four-stroke Z1 that had leapt out as a leading role for the era, were engineers pushing forward with development for a muscle two-stroke, the Square-Four 750 that came close to completion. Unfortunately, it was decided that development would be discontinued in August 1973 thanks to the influence of the American exhaust emission regulations. If only this machine had been produced it is likely that it would have topped the Z1.

(Kawasaki Square-Four 750   1973) This was the forerunner for the RG500 (1985) that would later appear, with a 750cc water-cooled, square-four engine. This phantom model was designed by the father of the Mach, Hiroyuki Matsumoto (deceased) and his team, as a successor for the straight-three cylinder series.

This is the Square-Four 750 that was photographed at the Kawasaki Motorcycle Fair that was held in February 2017. Maximum power output was not announced, but in August of 1973 when development was discontinued it was at a time when the Z1 was already on the market, so we reckon it would have entered a similar power range. Incidentally, the two-stroke, three-cylinder 750cc Mach 4 was 74bhp.

Development code (0280) was called “Steak tartare”

It was Kawasaki that always aimed to be the “fastest in the world”, and in 1971 it was the air-cooled, two-stroke, three-cylinder 750SS (Mach 4) that took the title of being the fastest bike on sale. However, due to market demands the contest for power increases had intensified. It was during this time of demands for even more power that secret development began under what was known as code number (0280), the Square-Four. What Kawasaki were aiming for in their development was to outdo the Mach by producing a machine with the fastest top speed and a degree of perfection, while retaining the engine capacity and peak power output of the 750SS. This was not done by relying on merely power for acceleration performance or top speed, but instead it was a pursuit of a new challenge to create a motorcycle with all-round performance. In order to stop the air resistance on front parts of the engine, a water-cooled, square-four compact layout was adopted, making the right front & rear cylinders and the left front & rear cylinders unified. The intake ports were connected respectively to the twin-carburettor, and a fuel injection system was also developed. The design was prioritised and a two-in-one exhaust pipe was created in order to prevent any power loss. Development was going well, and Kawasaki were not far off from achieving the numbers they had aimed for, but the project was stopped thanks to the influence of the American exhaust emission rules in August 1973. The ultra performance Square-Four machine was commonly known as “steak tartare” in house (perhaps this was a reference to the engine’s raw power?!), and it never saw the light of day, instead becoming a phantom model. *Kawasaki Exhibition Panel

The front and rear cylinders on the left and right are unified, with the left and right connected respectively to the twin-carburettor. It was explained how this four-cylinder machine differed from the Mach series because of how its overall width was kept down. It was also made clear in past news coverage how Matsumoto had also designed a fuel injection version, and the Kawasaki Exhibition Panel also has records of these activities. 

The meters were exclusively designed into square shapes to match the square-four engine. Due to being a water-cooled engine there is a water temperature gauge arranged in the centre. We had to wait for around six years until the first water-cooled Kawasaki would go on sale, with the Z1300 model in 1979.

The Mach series back in 1973 had a kick start, but you can see how the Square-Four seems to have a starter motor under the engine. There is also a kick start pedal on the right-hand side of the engine, so it appears it was designed to have both.

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本誌編集長。雑誌は生き残りタイアップ全盛期だというのに、ひとり次期型ネタを嗅ぎまわって反感を買う現代のスクープ魔王。
■1972年生まれ
■愛車:BMW R100GS(1988)

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