Eizaburo Uchinishi: the 2-stroke engine meister who conceived and developed KIPS.

When the term "exhaust device" first started coming up in bike conversations, it carried a "sorcery" or "slight of hand" nuance to it. Able to compensate for 2-stroke engines' weakness, it was a gadget that magically delivered torque… In any case, the craft plied by engine designers certainly was unique.
"We had a whole bunch of ideas. Although making them work for mass production was another story… We were able to build an engine by hand, and then go out and win with it. But that didn't mean anything if the technology couldn't be used in a mass-production motocrosser. When developing our exhaust device, ensuring it could be mass produced was always a requirement. That meant that development took a little longer, but I'm proud to say that the end result was a part with superior functionality."
Any discussion about the advances made by the KX Series would be incomplete without mentioning Eizaburo Uchinishi (chief motocross engine designer at the time), the man behind the development of KIPS (Kawasaki Integrated Power-valve System).
"Exhaust devices for 2-stroke engines can be divided into two types: those that offer exhaust port control, and those that offer exhaust chamber control. Motocrossers from rival manufacturers used either one or the other. The former type regulates the size of the exhaust port opening, making it smaller at low rpm and larger at high rpm. The latter added a resonator near the entrance of a high-rpm exhaust chamber, enabling chamber volume to be increased so that it could function as a low-rpm exhaust chamber as well. KIPS, the device we developed, did both. The first version, used on the 1985-model KX125 and KX250, had valves to operate exhaust sub-port and resonator openings simultaneously."

1986 KX125 engine. Although KIPS was used on the 1985 model KX machines, it was not until 1986 that the KIPS logo appeared on the cylinder head.

The first KIPS-equipped racers made their debut at Round 3 of the 1984 All-Japan Motocross Championship, at Hiroshima's Miyoshi Sogo Sportsland. In that first race, Atsushi Okabe (an International A-class rider for Team Kawasaki at the time) got 3rd overall and Mikio Tatewaki (same) got 5th. Then, at Round 4 at Suzuka Circuit, Tatewaki went 3-1 on his KIPS-equipped KX125SR, earning a very important first win.
"Without KIPS the 125 was peaky with a very narrow powerband, so if you faltered a little, or went off the race-line and let the revs drop, then it was really hard to recover. If you weren't always half-clutching you couldn't draw out the power – it was a very severe performance curve. But with KIPS, although response seemed a little less quick-revving, it was much easier to get low-end torque. It was like the engine would cover for any mistakes the rider made. At that Suzuka round, we were in the middle of a supercross boom, so there was a washboard section. On tricky parts of the course like that, KIPS was immediately effective."
As Tatewaki alluded, the increasing need for KIPS was not completely unrelated to the growing popularity of supercross. On layouts that featured multiple jumps right after tight corners, peaky engines just couldn't compete.
"We designed the first KIPS in about a year and a half. The 125 and 250 have different configurations, but the basic principle was the same, so after we designed the 125 version we applied it to the 250. We were able to achieve the performance we wanted, but getting the rods that opened and closed the valves to move smoothly was difficult. They warped due to the heat, got covered in unburned oil and would get stuck. Of course, these issues were cleared up in time for mass production."

Graph illustrating the effect of KIPS. Valves open and close according to engine speed, resulting in a smooth power curve extending from low rpm through high rpm.

Favourably received from its first year, KIPS continued to evolve with every model change. In addition to controlling exhaust sub-ports and resonator opening and closing, later versions added a valve to regulate timing of the main exhaust valve, and 2-stage 3-way KIPS also moved the sub-valves in two stages.

"With engine development, there's no such thing as point where we can say, ‘OK, we're done.' No matter how much performance increases, racers always want more. The ones we focused the most on pleasing were the American riders. But in reality, racers like Jeff Ward and Ron Lechien were unsuitable test riders. For example, Ward keeps the revs up and muscles his bike around corners – his cornering style in nothing like the average rider's. Lechien keeps the throttle wide open while braking and modulates the clutch – another style difficult to copy. The opinions of riders like Mike Fisher, who has a very common riding style and technique, were much more valuable to development. A 1 PS peak power gain on a 50 PS engine is only a 1/50 increase. But increasing low-mid output of 20 PS by 1 PS is a 1/20 gain, and is much easier to feel. That kind of thinking formed the basis for our efforts in developing KIPS."
Uchinishi has spent more than half of his life as a motocross engine designer, but the time has come for him to move on.
"I'm sure DNA from the KX Series will be passed down. At Kawasaki, factory racing activities and development of mass production models are both handled by the same small group. This results in a very tight-knit team – an asset that I hope will be preserved. Technology can be formally documented in blueprints and such, but to really be understood the thinking behind the technology needs to be passed from one person to the next. That's why I hope that the team will continue to be involved in both racing and model development."