In 1968, Kawasaki joined Suzuki in the production off-road machines. Unlike the Suzuki TM250 that was targeted at motocross, the Kawasaki F21 was designed for the smoother scrambles tracks of America.
Courtesy Motor Cross Action Magazine
The color brochure said, “Hit the Scrambles Trail on a Top-performer Built to Take it.” The 1968 Kawasaki F21 fuel tanks were painted a deep red with the Kawasaki aircraft company logos on both sides. In 1969, these bikes came equipped with a much brighter white and lime green tank design. The 1969 model, although not all the different from the red tank version was relabled as the F31-M Green Streak. Less than 1000 of these the F21 and F31 were produced from 1968 to 1970. It was the first Kawasaki mass produced race bike marketed for motocross, scrambles, hare scrambles and flattrack
Other than trying to tame down the power output, the 1968 and 1969 F21-F31 bikes were designed for the 250 class, but only came with a 238cc displacement and many potential buyers thought it was 250cc bike. The”238″ was not competitive against the 250 Bultacos, Ossas or even the and the Japanese Yamaha DT1 because of the displacement was not being a full 250. It was called the “Big Green Streak”, but sales wer sluggish, while its 100cc Green Streak brother was a rocketship on the track and flew off the dealer’s showroom floors.
The front forks look a lot like Italian Ceriani forks, but they Kawasaki’s own version, patterned on the popular Ceriani forks.

Because of the the rarity of 1968-69 Kawasaki F21/F31 rotary valve bike they hold a veru high resale prcie on the vintage market place—often going for anywhere from $12,000 to $20,000 depending on condition.
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