Kawasaki’s two-stroke Superbike, known in the factory as the 602, came out of the period immediately following the furore created by Yamaha TZ750. Shortly after the introduction of the big Yam, in the October of 1974, the homologation rules were changed meaning manufacturers only had to produce 25 machines thus making machines not based upon road based engines more feasible. With the new rules, Kawasaki quickly laid down the plans for their water-cooled triple, using many of the ideas for this machine on their already well-established H2R air-cooled triple. They worked fast and the all-new machine was ready for the Daytona 200 the following March. The design is a clever one, a 750cc triple has large diameter pistons and with them comes a huge width, not usually attributes needed for a world-class racer. The Kawasaki design team tackled this problem by allowing the huge transfers to sit diagonally opposed to the front of the piston while the exhaust and inlet ports sit askew too.
The real trick behind the KRs success can be found within the engine casings. Unlike the more prevalent, and far more complex TZ750, the Kwak keeps it simple, a one piece crank drives the clutch without resorting to an array of lay shafts, thus ensuring every single horsepower possible makes it way to the rear wheel. It weighs considerably less than a production TZ750 and a few kgs lighter than the mythical OW31 too, and with one less of each reciprocating engine component, the Kwak loses less power through friction losses.
The budget for this project was low, so small that the UK spec machines arrived with no port cast into the single block three cylinder barrels, the final porting was dictated by the Boyer team mechanics using data supplied from Japan. Several chassis items were junked by the UK team too, the original alloy brake discs soon found their way into the bin, to be replaced by more efficient steel items, while high spec Girling rear shocks took up their position at the rear end. The KR750 was super fast from the outset and, while the privateers struggled to get the Yamaha up to speed, the factory green meanie saw top form although reliability issues did thwart its early attempts at race success.
The KR first appeared at the 75 Daytona race with a five-rider factory effort, Canadian, Yvon DuHamel was joined by Jim Evans from the US team, Barry Ditchburn and Mick Grant from the UK and Japans Takao Abe. None of the five KRs finished the race however, persistent crank problems scuppering most and a seized gearbox taking out Ditchburn. This was early days for the speedily developed racer however and soon most problems where ironed out although the problem of a crank life of around 200miles did continue for some time.
In the southern hemisphere the Australian team found that the air-cooled H2R was faster at the top end and remained faithful to the type when top speed was needed. Strangely, two years after the introduction of the KR750, the old H2R was still winning races; Gregg Hansford lapped the Bathurst circuit two seconds faster on his old H2R than he had on the newer KR750 and development of the older model continued in Australia for some time after 1974.
Riding the KR does open the riders eyes somewhat, the triple is a real screamin demon, unlike the relatively tame TZ and TR750 Suzuki, a real mans two stroke with a power delivery more akin to a highly tuned Moto X machine than a big capacity road race bike. Not that many will have had the opportunity to sample this factory machine, just 20 were produced between 1975 and 1978, making it one of the rarest of all race machines. The Kwak twists and weaves its way along a racing line, not because the chassis is poor, far from it, the tube work is excellent but more due to the way the engine comes on song, twisting even the most sturdy metal work as the power makes its way to the rear tyre.
Evidence of the KRs speed is well documented, when they held together they won and when they didn’t, often the fastest lap of the race would be credited to a Kawasaki rider. At the TT in 1978, Mick Grant on the KR750 pictured here, was timed at a staggering 192mph on his Kwak, while Gary Nixon so nearly became America’s first motorcycle world champion in 1976, where it not for a timing error at the Venezuelan F750 round. The results of that race where deemed so confusing that the round was discounted totally effectively robbing Nixon of the world title.
During 1977 a new KR, the 602L was delivered to the UK team for Grant and his teammate Barry Ditchburn to use. This was to be the final version of this short-lived race bike and featured magnesium crank casings, a lightweight clutch and extensive weight saving measure throughout. This new model tipped the scales at a respectable 136kg, and produced around 130bhp, but even so they had a hard time beating the TZ thanks mainly to the kwak fiery power delivery, although on the road circuits of the UK Grant was nothing less than awesome during this year with lap records a race wins alike.
By 1978 the KR had seen the best of its days and factory support had all but diminished, efforts back at the factory had turned to an all-new four-cylinder race engine, the 602S. This featured a strange, trapezoid cylinder arrangement that allowed the engine to be even narrower (50mm) than the triple that preceded it. Two of the reed-valve 750cc engines where produced and rumoured to produce around 145bhp, one engine was slotted into a KR like chassis and showed much promise, Australian Hansford riding it in practise at the Italian 750 round, but electing to use the older triple for the race after vibration with the four proved troublesome. The 602S was returned to Japan never to be seen again and with end F750 racing being forecast some time before work began, it is more likely that this design was really the basis of Kawasaki’s entry into 500GP racing, albeit when they did return it was with a square-four, disc-valve machine.
The KR750 is often forgotten in an era that remembers the Yamaha TZ far more favourably, but it was the machine that kept the opposition on its toes race after race. Then be no doubt the KR was hard to get the best out of, but Kawasaki saw fit to sit only the best in that green saddle.
Kawasaki KR750 Specifications
- Engine – Water-cooled, three-cylinder, piston-port, two-stroke
- Capacity – 747cc
- Bore/stroke – 68mm x 68mm
- Power – 125bhp at 9500rpm
- Torque – 70ft-lb @ 8700rpm
- Carburetion – Three 38mm Mikunis
- Ignition – Kawasaki CDI
- Transmission – 6-speed dry clutch, chain final drive
- Frame – Kawasaki steel tube
- Suspension – 38mm Kayaba telescopic forks, Girling rear shocks
- Brakes – 296mm discs twin piston calipers, 260mm disc twin piston caliper
- Wheels – 3.75 x 18 4.50 x 18
- Weight – 136kgs
- Top speed – 180 mph depending on gearing
- Wheelbase – 1430mm
- Fuel capacity – 22lts
Kawasaki KR750 Gallery