It may be hard to imagine for riders who have gotten into motorcycling over the last 40 years that there was a time when two-strokes were legitimate street bikes. Some of them, including the 1968 Kawasaki H1 Mach III 500 two-stroke triple, were both lionized and feared. While the motor delivered the power to annihilate all comers when the light turned green, the chassis fell far short of the engine development.
Although Yamaha, Triumph, and MV Agusta are now renowned for their three-cylinder motorcycles, Kawasaki had a broad range of two-stroke triples sitting on showroom floors in the early 1970s. At the top of the Kawasaki two-stroke food chain was the H2 Mach IV 750. The Mach III 500 was made more civilized. Below that was the S2 Mach II 350, which grew into the S3 Mach II 400.
The baby of the line, and the story’s subject, is the 1973 Kawasaki S1 Mach I 250 three-cylinder, air-cooled two-stroke. It was an undersquare design with a 52.3mm stroke matched to a 45.0mm bore to give the kickstarted motor a shot at producing torque. Yep, each cylinder displaced just 83cc, and was fed by a 22mm Mikuni carb. Lubrication was via automatic oil injection.
The motor topped out at 30 horses at 7500 rpm, with the torque peaking at about 20 ft-lbs at 7000 rpm. As you can imagine, it loved to and needed to rev. With a curb weight of around 360 pounds and a straight-cut five-speed gearbox, the 1973 Kawasaki S1 Mach I could score 95 mph on the likely-optimistic speedo. The wheelbase was 32mm, so that had to be quite a ride on the 18-inch wheels.
The Kawasaki S1 Mach 1 was sold from 1973 to 1975. Its closely related KH250 successor lasted until 1980. This 1973 example, with 6887 miles on the odometer, Candy Gold paint, the tool kit, and plenty of paperwork, sold for $6600 at Mecum Auction’s Indy 2024 event this spring. As the included receipt reveals, the bike went out of the Loomis Cycle Sales shop doors in Hammond, Indiana, on July 11, 1973, for $926 ($6550 in 2024 dollars).
