HORN AGAIN
Bizarrely, Kawasaki’s Bighorn enduro bike was transformed into this front-running road racer. Here’s how it happened
How Kawasaki USA took on road racing greats with their hopped-up Bighorn trailie
The Bighorn became a racer thanks to the AMA (American Motorcycle Association) changing the rules for their Lightweight racing class in late 1971. The class was dominated by Yamaha’s 250cc twins, but in hope of attracting more manufacturers and provide greater interest for fans, the AMA decided to allow single-cylinder two-strokes up to 360cc into the National Championship. This capacity was a popular one in motocross bikes by the likes of Husqvarna, Bultaco, Suzuki and Yamaha – and its road-racing potential had been proved by New Zealander Ginger Molloy who got on to the podium in the 1969 500cc Spanish GP on a Bultaco 360. However, US importers of 360cc motocross machines showed little interest in the new concept. Only Kawasaki thought it was worth experimentation – and the resulting Bighorn-based racer became a genuine contender in the Lightweight series. Kawasaki America’s road racing was run Bob Hansen for 1972, with the bikes entered under Team Hansen. Bob put together three 350cc single-cylinder racers, using the rotary-valve two-stroke from the F5 Bighorn enduro, fitted into some A1-R chassis left over from Kawasaki’s earlier 250cc twin-cylinder racing programme. With cylinder porting, a larger carburettor and suitable expansion-chamber exhaust, the tuned version of the F5-R immediately outperformed the A1-R twins of the late ’60s. It proved surprisingly competitive at the short, tight layout at Loudon; Gary Fisher and Kenny Roberts were first and second on Yamaha’s factory 250cc twins, but Yvon Duhamel came third on his Kawasaki and Paul Smart fifth. The Bighorn was an unlikely challenger, yet much more effective than expected.
Responsibility for the team was back ‘in house’ for 1973, with Randy Hall taking over as team manager and development engineer. Continuing what Hansen had started, he entered Yvon Duhamel and Art Baumann in the Lightweight race at the 1973 season-opener at Daytona on bikes with the A1-R racing chassis but updated with the latest 350cc Kawasaki F9 engine. These were designated F9-RA and had been built with help from an unusual source. Hall had spent three years in Europe engineering Rod Gould’s Yamaha racers, which culminated in Gould winning the 1970 World Championship, and had become friendly with Dr Gordon Blair, professor of engineering at Queen’s University in Belfast. They stayed in close contact after Hall returned to the USA, and came to a development agreement.
Blair was well known to British race fans for his work on QUB racers ridden with success by Brian Steenson and Ray Mccullough in the late 1960s and early ’70s. The QUB 250 was a water-cooled two-stroke twin with a unique rotary sleeve in the cylinder bore that controlled induction and exhaust timing, and produced 45bhp – close to Yamaha’s power at the time. There was also a QUB 500, an air-cooled two-stroke single in a Seeley chassis, on which Ray Mccullough won races in Ireland.
When Hall discussed the Bighorn project, Dr Blair saw parallels with his own ‘big single’ two-stroke project. He