Classic bike: Kawasaki KH250
While the KH250 was the smallest of the legendary Kawasaki triples, it may well have been the pick of the bunchDuring the 1960s the Japanese economy experienced a time of tremendous growth, and a corresponding surge in motorcycle production. And along with other manufacturers, Kawasaki was swept along on this wave, a phenomenon that would later be called the ‘Inzanagi Boom’.
This led to a proliferation of new models, and after Honda released its CB450 ‘Black Bomber’ and Suzuki the 500 Titan, Kawasaki needed a performance flagship to compete.
It responded in late 1968 with one of the most charismatic performance motorcycles ever produced, the 500cc three-cylinder two-stroke H1, or Mach III. This set Kawasaki on a path of two-stroke triple development that was out of sync with other manufacturers, but led to an impressive line-up of models with this engine format over the next few years.
Intent on capturing the lucrative US market, 1972 saw Kawasaki release a range of three-cylinder two-strokes alongside the H1. These were the smaller 350cc S2 (Mach II), 250cc S1 (Mach I), and the 750cc H2 (Mach IV).
The S2 and S1 were replacements for the ageing A7 and A1 twins and looked like scaled down versions of their larger brothers except for the retention of the front drum brake, while the H2 was the new fire-breathing superbike.
The baby of the triples, the 250cc S1, became the S1A in 1973, the S1B in 1974, and S1C in 1975, before evolving into the final version, the KH250 in 1976.
Apart from colours and cosmetics the KH250 was ostensibly identical to the S1. The piston-port air-cooled triple followed the lines of the H1 but with a slightly different lubrication system. All the triples shared a pressed-up crankshaft design and five-speed indirect gearbox.
On the S1 a bore and stroke of 45mm x 52.3mm provided 249.5cc, the compression ratio was 7.3:1 and with three Mikuni VM22SC carburettors the S1 produced a creditable 23.5kW (32hp) at 8500rpm. Unlike the H1 that had groundbreaking CDI ignition that wasn’t totally reliable, the S1 and KH250 each had a traditional battery and coil ignition. This featured three pairs of points mounted on the left, outboard of the 110W alternator.
Because the S1 was quite difficult to live with and was also extremely thirsty, when the updated KH250 appeared its maximum power was reduced to 20.6kW (28hp) at 7500rpm. Although the new engine was easier to live with, the bike’s performance suffered and the top speed was reduced from around 165km/h to 150km/h.
The KH250 also included some chassis improvements over the S1. While the drum front brake was still available in 1976 on the KH250-A1, the B1 model of the same year offered a 226mm front disc brake. Unfortunately the weight also increased, from 148kg to 158kg, but the KH250 was still a remarkably agile and nimble machine.
The wheelbase was only 1375mm and the little KH rolled on a pair of 18-inch wheels shod with typical 1970s skinny tyres.
These little triples were just great fun to ride. Unlike their larger brothers there was never any threat of the engine overpowering the chassis. But being two-strokes they were still thirsty; as a result the oil crisis of 1974 threatened them with extinction, along with all two-strokes.
Against all odds the little Kawasaki triples survived, but it was only a matter of time before they too disappeared. The two-stroke era will never return and now all the Kawasaki triples have become machines with a cult following.
Thanks to Allen and Lorraine Smith of the Australian Motorcycle Museum in Haigslea (Qld) for the use of the 1976 KH250-B1 featured.
FAST FACTS
- Although overshadowed by its bigger brothers, the 250 was the most popular of all the Kawasaki triples.
- In the UK in particular the S1 and KH250 were learner legal and particularly fashionable as they were amongst the highest performing 250s available.
- While the 750 H2 finished in 1975, the 500 H1 in 1976, and the KH400 in 1978, the KH250 outlasted them all. The final KH250-B5 was produced in 1980.
- Because the triples were air-cooled with pressed-up cranks it was possible to cut an engine apart and add cylinders and sections. Five and seven cylinder engines, and even a V6 were successfully built out of 250 triples.
- These multi-cylinder offshoots were most popular in Europe where they were seen as an example of a machinist’s skill. The most bizarre was a 48-cylinder bike made out of sixteen 250s.
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Story courtesy of Motorcycle Trader magazine.
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