The KX series came about as a direct result of Kawasaki’s first forays into motocross competition and the full-fledged factory efforts that followed.
Since that time, the KX series has continued to grow at a rapid pace.

The Dawn of
Motocross History

In the earliest days of motocross competition, when Kawasaki began to dominate the field, Kawasaki machines were recognised by their red fuel tanks. The first racing machines produced were based on motorcycles intended for daily use. When Kawasaki’s in-house team first entered MFJ competition in 1963, it swept the first six places, and marked the start of selling motocross machines as production models. As the lineup of models with red fuel tanks gradually increased, sales in various parts of Japan rose during the motocross boom, and the company soon became known as "Red-tank Kawasaki.”
When the All Japan Motocross Championship became an official series, Kawasaki factory rider Takashi Yamamoto reigned as champion in two classes (90 and 250 in 1967, 250 in 1968, and 90 in 1969). Then, Kazuyoshi Hoshino, who would later become a car racer, also won a double title (90 and 125 in 1968).

Top, Bottom-Left: Kawasaki’s first motocross, the BM8, debuted in 1963. It had a 123.5 cm3 displacement. Factory racers with Parallel Twin engine configurations were also created.
Bottom-Right: Sales of the F21M, a 250cc-class motocrosser, began in 1967. (1968 model shown here) This model captured back-to-back titles in the All Japan Motocross Championship in 1967 and 1968.

More Opportunities
for Development –
The First Breaths
of the KX

It was true handmade craftsmanship that went into producing machines in the early days of the “Red-tank” racers, with engines and frames produced and tuned to suit each rider’s needs.
Eventually, as riders in and outside Japan made demands for more availability and improved performance from production models, Kawasaki changed its internal organisation to focus on full-fledged factory racing activities. In April 1972, Development Team 1 was established in Kawasaki’s Engineering Department. It went on to become the brand’s most pivotal department specialising in road racing and motocross racing machines.
As consistency emerged from the development stage through racing and into production models, the start of what is now known as the “KX” series—the KX name included the meaning “Kawasaki’s ultimate motocrossers”—began. The design concept was extremely simple: these machines were “Built to win.” The first priority was to contest the World Grand Prix, and Olle Pettersson was contracted as a development rider toward that goal. KXs were designed to compete in three categories: 125, 250, and 500.

Development testing in Europe.
Frame welding and other work was conducted locally, and rider feedback was quickly incorporated.

At that time, as the AMA Motocross Championship was still in its infancy in the United States, post-season motocross events like the Trans-AMA and Inter-AMA featuring European riders were extremely popular. In contesting these, Kawasaki competed in a battleground dominated mostly by European manufacturers, and in the process produced American champions like Brad Lackey (1972 AMA MX500) and Jimmy Weinert (1974 AMA MX500 and 1976 AMA SX250).
Alongside factory racing activities, production KX models were offered to the public from 1973. To enhance the brand's presence, Lime Green was used as the signature colour. Previously, Lime Green had been used on the A7RS and A1RAS factory machines at the 1969 Daytona 200 and had been tried on F-series and other motocross machines following that. Initially limited to the fuel tanks, the colour gradually became part of the KX identity, with fenders and side covers also carrying the now-recognised Lime Green.

Sales of KX machines began in 1973. (Left: KX250, Top-Right: KX125)
From that point on, development and sales of the KX series have continued unbroken without a single year’s break.
The “KX” name has adorned the bodywork since 1975 (Bottom-Right).

Rapid Growth

The most outstanding progress the KX series made in the 1970s was developments in suspension technology. The 1973 model’s stroke was only 185 mm at the front and 90 mm at the rear, but in less than 10 years that number had increased to 300 mm at the front, with the machine also growing in size to accommodate. The suspension’s progression also reflected technological innovations, like De Carbon-type units that contained nitrogen gas inside the shock.
To slim the engine down, the intake system moved from rotary disc valves to piston valves, and when the material used to make reeds improved, piston reed valves became the norm. For the exhaust, the chamber went from an upward-facing design to downward-facing, and then back to upward again. This was because having it facing downward allowed an increase in volume, but as time went on ground clearance became an issue, and the design became upward-facing. The upward-facing chamber had the disadvantage of being in the way of the rider’s knees when gripping the bike, but this was addressed at the design stage by careful consideration and placement.
One trend during this time was using aluminium and magnesium to reduce weight as much as possible. In 1976, Shoji Takezawa took Kawasaki’s first All Japan title in eight years on his factory KX250SR machine. To make the large machine easier to handle, the design featured a 17-inch rear tyre and used lighter parts used throughout. This idea of size-reduction was then used in the design of the KL250 dual-purpose model that debuted later that year.

The 1978 KX250 with piston reed valves and upward-facing exhaust.
In just five years since the introduction of the first model, the significantly increased suspension stroke and ground clearance is easy to see.

The KX’s “Built to Win” design concept remains unchanged even now, at the iconic series’ 50th anniversary. The technology that went into designing and building Kawasaki’s motocross machines, always aiming to be the most competitive, has been passed down to all of Kawasaki’s motocross-derived machines through the years.