Kawasaki 50th Anniversary:The Green Monsters

42 years ago the KX models laid down the groundwork for Kawasaki's motocross lineup

Kawasaki KX125, KX450F, KX250, KX450, Green Monsters
From the industry-changing 1974 KX125 to today's title-winning KX450F, Kawasaki has and will continue to transform the industry.Photo Courtesy of Kawasaki

Motocross was a firestorm in the early 1970s, with numerous Japanese, European and even American motorcycle companies all scrambling to develop the right technological combination to win professional races, in the hands of weekend warriors, and on the showroom floor. The challenges were many, including quickly evolving engine, chassis and suspension designs that would all work well together. Piston-port and rotary-valve two strokes, and pushrod and overhead-cam four strokes, from 100cc to over 500cc all battled for the winning edge, with more than a dozen manufacturers competing for customers’ attention in a fast-growing sport. Motocross truly was a melting pot of technology at the time.

Thanks to the excellent groundwork established by Kawasaki’s 1972 championship-winning prototype F12MX program, in 1974 Kawasaki launched an industry-changing lineup of KX125, KX250, and KX450 motocross motorcycles—a complete range of race-ready machines all finished in Kawasaki’s characteristic Lime Green paint. It was the broadest, meanest and most technologically advanced range of machines of any Japanese manufacturer in the day.

  • The KX125 used a new rotary-valve two-stroke engine evolved from the engineering lessons learned from the high-output 1970 100 Centurion G31M dirt racer. Weighing 199 pounds, with its electrofusion-coated cylinder and six-speed gearbox, the 1974 KX125 immediately became a threat to win any 125 motocross race.

  • The KX250 anchored Kawasaki's new MX lineup with explosive two-stroke power, – along with such innovations as fade-resistant Hammerhead shocks. Dent-resistant plastic fenders kept weight to 214 pounds.

  • The range-topping KX450 delivered heroic power that only top riders could fully utilize—among them, 1974 AMA 500 Motocross champion Jimmy Weinert. A plastic fuel tank and fenders helped pare weight to just 220 pounds, making the KX450 a motocross missile.

Kawasaki, KX450, KX450F
From the 1974 KX450 to today's KX450F (pictured).Photo Courtesy of Kawasaki

At their launch 42 years ago, the first KX motocross motorcycles made Kawasaki a powerful force in the most important racing classes. Every year since, the engineering and performance of the KX line has steadily improved, culminating today in the championship-winning KX65, KX85 and KX100 two-strokes, as well as the AMA Motocross and Supercross title-winning KX250F and KX450F four-strokes. Although faster and stronger in every way, each KX model shares the same competitive spirit as the three original 1974 green monsters. Roost on!