1971 Kawasaki F8 Bison 250, Frame no. F8008482 Engine no. F8E08737

1971 Kawasaki F8 Bison 250
Frame no. F8008482
Engine no. F8E08737
• Rare 'Baby Bighorn' 250cc version of the F5 350
• Older Marbles Motors restoration
• Showing 600 light-use miles since restoration
• Hatta fork, rotary-valve induction

Starting in the late 1960s with its F-series of dual-purpose bikes, Kawasaki made a strong play for U.S. on/off-road riders. Best remembered is the biggest, the F5 Bighorn 350, but a 250cc version was also available, the F8 Bison, identical to its big brother except for a smaller piston, different paint and a 19in. front wheel in place of the F5's 21-incher. Out in the field it soon became known as the "Baby Bighorn."

Kawasaki's fondness for rotary-valve induction on its two-strokes usually translated into class-leading horsepower, a trait upheld with the F5 and F8. The Klemm Vintage speed shop has a long history with the bikes, and successfully road races a Bighorn in AHRMA vintage events. "Of all the vintage enduros of the day, the Bighorn 350 and Bison 250 had by far the best overall power output, along with reliability that easily matched all the rest," they say.

Kawasaki's rotary-valve setup used a thin hardened-steel disc (more pork chop shaped, actually) mounted to the crankshaft between the right end of the crankcase and an outboard-mounted carburetor. The spinning disc controlled intake timing, advantages being that the intake port is open and unobstructed for a long time, and that the timing can be "asymmetrical," which allows engineers the option of boosting low-end power, a feature Kawasaki took full advantage of. Biggest disadvantage of the system is the added engine width caused by the carburetor being hung out on the right side, but on the F5 and F8 the carb was tucked in nicely, sealed in its own housing that provided protection from the elements, not to mention rocks and passing puckerbushes.

Both bikes were equipped with the so-called Hatta fork, a multi-adjustable unit with three axle positions, 4in. of stanchion-tube adjustment and three-way spring preload, quite advanced for the time. Cycle World magazine had no suspension complaints during their test of the 350, claiming, "The Bighorn is one of the few dual-purpose machines that we would take unmodified, lights and all, to a woods or desert enduro."

Today, restored examples of either machine are rare finds, simply because spare parts are so difficult to source. This 1971 Bison was expertly restored by Marbles Motors some years back, and was recently re-acquired by the shop from the owner after 600 happy miles had been logged. It still runs well, we're told, showing only minor patina from its light use.