In this article, we'll take a look at the brand-new, technologically advanced, and stylish Kawasaki KX250 "Works Replica" model from 1985.

The history of Kawasaki motocross bikes dates back to the distant year of 1963 when the "green" team became the first among Japanese manufacturers to introduce their off-road racing motorcycle. The company has always strived to stay ahead in terms of innovation and new technologies. Regardless of their success, Kawasaki continues to experiment with new ideas and always move forward. This innovative spirit has fostered fierce competition and has paved the way for many legendary racers in the sport.

In the late '70s, there was a race among Japanese manufacturers to develop new suspension technologies for motocross bikes, and Kawasaki took a significant step in this direction. In 1980, they introduced their lineup of motocross machines with a new rear mono-suspension system called "Uni-Trak" (initially known as the "Bell Crank"). It was, in fact, the most significant suspension innovation since Yamaha's introduction of the mono-shock system in 1975.

The early '80s proved to be a challenging time for Kawasaki. Their KX250 and KX500 models stood out more for their quirky style and problematic reliability than for their performance on the track. Cracked frames, broken hubs, leaking exhaust pipes, and fragile plastics were part of the unfortunate ownership experience with the "green machines" at that time.

In 1982, Kawasaki became the first manufacturer from the "Big Four" to equip their motorcycles with front disc brakes. This was a crucial innovation at the time as the existing drum brakes were struggling to cope with the increased power and suspension capabilities. Over the years, drum brakes had proven their efficiency and reliability, but their days were numbered. Nevertheless, this new feature was not favored by many riders who preferred the comfort of the familiar drum brakes. However, as the future showed, Kawasaki's bold move with the new technology was indeed the right one.

Two years later, in 1984, the company introduced the new KX250 model, which was the first to be equipped with liquid cooling, a powerful front disc brake, and the Uni-Trak central shock suspension. The engine had a strong low-to-midrange pull, but the transmission and clutch left something to be desired. The long and tall frame complicated turns, and the suspension sagged, knocked, and swayed on the track. The bulky ergonomics suited tall riders well, but if you were of shorter stature, you might have considered better options from other manufacturers.

While the 1984 KX250 model didn't achieve great success, its "younger siblings" KX60, KX80, and KX125 outperformed their competitors with appropriately sized frames, excellent handling, and powerful engines. In 1985, Kawasaki's engineers hoped to bring some of that success to the 250cc class by completely redesigning their platform. Everything, from the frame to the plastics, was entirely new, with a focus on improving handling, ergonomics, and broadening the powerband's usability.

In 1985, the new Kawasaki KX125 and KX250 models received a new power valve system called the Integrated Power-valve System (KIPS). Both machines featured a simple and lightweight design, along with an impressive peak power output, making them highly attractive for racing.

It's worth noting that in the '70s, adding a power valve had helped improve the engine's response to throttle input, and transitioning to liquid cooling in the early '80s, combined with new carburetors, helped manufacturers increase horsepower. Motorcycles were becoming more powerful every year, with engines becoming "explosive" and extremely fast. However, they generally still had a narrow powerband.

In response to this, manufacturers began to address the issue, and in 1982, Yamaha took the first step towards a solution by introducing the Yamaha Power Valve System (YPVS). This allowed engineers to optimize the characteristics for a broader range of riding conditions.

In 1984, Honda introduced its version of a power valve system called the Automatic Torque Amplification Chamber (ATAC). The ATAC system differed from Yamaha's valve but aimed to expand the powerband by adding a small sub-chamber on the exhaust.

Finally, in 1985, it was Kawasaki's turn to unveil its own power valve system, dubbed the Kawasaki Integrated Power-valve System (KIPS). Compared to its competitors, the new KIPS design optimally integrated new technologies. It was the brainchild of Etsaburo Uchinishi, the chief engine designer for motocross, who managed to combine the ATAC and YPVS systems into one mechanism, presenting his unique solution.

At first glance, the most significant change in the 1985 KX250 was its radically redesigned appearance. The 1984 KX250 had a rather quirky look, blending design elements from both the old and new schools. The disc brakes and radiator shrouds tied it to the '80s, while the rear fender number plate harked back to FIM rules of the late '70s. It was a strange mix of old and new styles that riders either loved for its uniqueness or disliked for its lack of elegance and taste.

All that changed in 1985, and the new model featured smoother lines, more compact dimensions, and the abandonment of the rear fender used since 1982. The new fender became longer and wider to increase mud protection and no longer used the "Euro" brace seen in 1984. The completely new 7.9-liter fuel tank had a slimmer layout, making it easier for riders to slide forward in turns. Relocated radiators were positioned 6 cm lower on the frame, and the new blue seat boasted a beautifully redesigned KX logo and sat 10 mm lower. The updated side panels provided increased protection from hot exhaust gases. Overall, the KX's ergonomics were significantly improved for riders under 170 cm tall, making it more in line with other Japanese competitors. While the new layout was well-received by most, long-time Kawasaki loyalists could revert to the previous ergonomics by installing a taller seat and flipping the offset handlebar mounts.

In addition to the redesigned appearance, the 1985 KX250 featured a revised frame to enhance handling and reduce weight. The entirely new high-tensile steel (HTS) frame had smaller dimensions and more aggressive geometry for improved handling. The wheelbase was reduced by almost 2.5 cm, and extra gussets were added in critical areas to prevent cracking issues that had plagued previous Kawasaki frames. The entirely new Uni-Trak rear suspension system featured a modernized linkage mechanism that allowed precise adjustment of the bike's ride height with an adjustable rocker arm.

It's worth noting that the 1985 KX250 received one of the most advanced rear shocks ever seen on production motorcycles. The new Kayaba shock offered separate high and low-speed compression adjustments, a multi-level adjustability that wouldn't become a common industry practice for over a decade. The shock had a travel of 320 mm and had four selectable high-speed compression settings and twelve low-speed settings. Rebound damping could also be adjusted with four available settings. In addition to nearly unlimited adjustability, the new shock featured an innovative overheating protection system through the use of an automatic thermal compensator. As the temperature inside the shock increased, a conical needle valve engaged to increase damping force.

The front suspension of the KX250 underwent a more traditional design. The bike featured an entirely new 43mm front fork from Kayaba, offering 299mm of travel and eight available compression adjustments. Rebound control was not externally adjustable, but a new three-way mechanical adjuster was integrated into the top of each fork leg to precisely tune the spring preload. Inside, the fork remained of conventional construction, but some new aluminum alloy components were added to reduce weight. To minimize the risk of the fork getting stuck in ruts, the protrusion under the front axle was reduced, and the fork guards from 1984 were removed to allow more cooling air to reach the relocated radiators.

Both the front and rear axles were upgraded in 1985, with the front axle diameter increasing by 2mm and the rear by 3mm. The braking system remained a combination of a front disc brake and a rear drum brake, but the rear received an improved backing plate with better sealing, and the front disc was 10mm larger.

As for the engine, it too underwent a complete overhaul. In 1984, the KX250 had a powerful engine but with a narrow powerband. The bike was quick between turns, but lacked the powerful torque of the class-leading Honda CR250R. In 1985, Kawasaki engineers sought to broaden the power range and developed their version of a power valve system - the Kawasaki Integrated Power-valve System (KIPS). It combined elements of Yamaha's adjustable YPVS (Yamaha Power Valve System) and Honda's exhaust resonance chamber ATAC (Automatic Torque Amplification Chamber). The engineers believed that by altering the synchronization of the exhaust port and changing the exhaust system's geometry, they could achieve the optimal balance of power and user-friendliness.

To accommodate the new KIPS mechanism, Kawasaki engineers had to completely redesign the engine. The cylinder, head, and crankcase were reworked to work with the new adjustable exhaust system. The updated cylinder retained the same piston diameter and stroke as the previous design but featured completely new channels and relocated the main exhaust port to the center of the cylinder. The displacement remained at 249cc, and the compression ratio remained the same (9.1:1) as in 1984. The redesigned channels in the cylinder and head improved coolant flow and helped prevent detonation under heavy loads. To address ignition failures that had plagued the 1984 KX250, the spark plug cap was reinforced, and the crankshaft contacts were increased to ensure a reliable connection.

Fuel delivery was handled by a new 40mm Mikuni VM40SS carburetor (2mm larger than the 1984 model) with a flat-slide "R-shaped" valve that, according to the engineers, provided better fuel atomization at low RPMs. The completely new air filter box was increased in volume, and an innovative new Fresh Air Intake System (FAIS) drew air directly from behind the front number plate. The FAIS consisted of a tube that ran from the rear of the radiators along the spine of the main frame to the top of the airbox, allowing cooler and fresher air to be delivered to the engine for increased performance. In addition to the air intake, the engine received a redesigned reed valve and an entirely new intake manifold. The new reed valve featured air guides in its construction to reduce turbulence and eight carbon fiber reed petals, providing lightning-fast throttle response.

The new radiators were longer to improve cooling efficiency but also lower to make the rider's workspace more comfortable. The new exhaust better hugged the fuel tank and had a completely new shape specially designed to work with the KIPS.

The engine also received an entirely new floating-type clutch and a reworked clutch lever for improved feel. The clutch housing no longer featured a quick-change clutch cover but instead had a convenient inspection window for quick oil level checks. The five-speed gearbox remained with closely spaced ratios, and all gear ratios remained unchanged from 1984. The new gearshift lever had an aluminum construction, a folding tip, and a modified shape for more reliable shifting.

Although the KX250 engine had sufficient torque, the clutch and transmission remained significant obstacles to its optimal performance. The upgraded clutch had a light pull, but its function was unsatisfactory. The bike's sluggish response at low RPMs demanded the rider to use excessive clutch lever action outside of corners, quickly exceeding the rider's patience with such abuse. Engaging and disengaging the clutch made it challenging to harness the bike's power effectively, and even skilled riders found it difficult to modulate the sharp power delivery of the KX250. Off the corners, the clutch would grab, and riders often had to roll off the throttle before the next shift. In theory, the new engine seemed competitive, but in reality, it fell short of the expectations of loyal Kawasaki fans.

Regarding handling, the KX250 was improved but still lagged behind the best bikes in its class. Weighing in at 98.8 kg, it was 1.36 kg lighter than the 1984 model, making it the lightest among all Japanese motocross bikes in 1985. This weight reduction provided significant advantages on the track, where the KX250 felt agile in the air and easy to flick from one turn to the next. It was a capable "jumper," and almost everyone noticed how much easier the new bike was to handle compared to the previous year. Cornering precision improved significantly from previous models but still fell short of the Honda CR250R. The front end of the Kawasaki never felt entirely planted in corners, and the bike tended to stand up in the middle of a turn if the rider's technique wasn't precise. On corner exit, the sharp power delivery and hard-to-modulate clutch made handling challenging, with the bike either spinning the rear wheel or abruptly catching the clutch and unloading the front end.

At speed, the bike was well-balanced and did not exhibit the tendency to headshake like the Honda. An occasional kick from the rear suspension could upset the handling, but the Kawasaki never tried to tear the handlebars out of your hands or snap you off like a fly if you hit a bump at high speed. Overall, it was a well-handling bike that excelled in jumping. It also ran confidently at high speeds on straightaways but demanded more skill and concentration in corners compared to its competitors.

Thanks to the most sophisticated suspension in its class, the 1985 KX250 had many advantages. The Uni-Trak rear suspension offered almost endless tuning possibilities with its adjustable linkage system. For those well-versed in suspension theory, this opened up a whole world of possibilities, but it also made it easy to get lost in the tuning process. Of course, it was easy to make mistakes, but when the rear suspension was correctly dialed in, it proved to be highly competitive. Some fast riders felt that the stock spring was a bit soft, and the rebound on the KYB shock was slightly too fast, but overall, it smoothed out the track very well. As long as you didn't mess with the rear shock too much, sag was not a problem, and many riders considered the rear suspension to be one of the best available in 1985.

Regarding the KYB front fork, it was much less mysterious and, in most cases, worked very well. The standard springs were slightly soft for professionals, and they complained that the rebound was too fast. Certainly, without external rebound adjustment, setting up the fork was not easy, but riders with more modest abilities found the fork simply excellent. The externally adjustable spring preload was taken straight from Jeff Ward's factory bike and provided a level of adjustability that competitors lacked. With this adjustment and eight compression settings, most riders could find a setup that worked well. While some riders complained of mid-stroke harshness when the bike was new, this improved as the suspension wore in.

As for the details, the bike was a bit of a mixed bag. Technically, it was the most advanced machine in its class, with factory-level suspension, a dual-function power valve, a clever air intake system, and a good front fork. The adjustable linkage allowed for changing the ride height, and the offset reversible handlebar clamp offered more comfortable settings. It was an 80s motocross bike with all the bells and whistles any respectable rider would want, and while this level of technology was welcomed by most, not every innovation proved to be a blessing.

The adjustability of the suspension was not extensively described in the user manual, and many found its numerous settings simply unfathomable. The new adjustable linkage also turned out to be a primary cause of breakages as many riders would bend it at the adjustment point. Frame failures were still common, and the footpegs left room for improvement. The quality of plastics and hardware was poor; fenders broke easily, and bolts stripped effortlessly. The stock sprocket and chain were made of cast iron, but this was the norm for Japanese bikes of that time. Overall, engine reliability was good, but the KIPS power valve system significantly complicated maintenance, and the electro-fusion cylinder plating used by Kawasaki made repairs extremely expensive. Vibration was also the most prominent among the "Big Four" bikes, with more than a light tingle transmitted through the handlebars, but again, this was par for the course for Japanese bikes of that era.

Rubber Trick covers protected the throttle, clutch, and front brake controls, while most riders found the bend of the standard handlebar appealing. The bike was slim and comfortable, and many riders were torn between Honda and Kawasaki as the green machine offered superior ergonomics in 1985. The front and rear brakes were powerful, with the front disc only falling short of Honda's excellent dual-piston brake. Despite these strong points, many riders noted issues with contamination in the Kawasaki's hydraulic system. This quickly turned the front brake feel to mush as the system required more frequent bleeding compared to its competitors.

Overall, the 1985 Kawasaki KX250 proved to be a solid machine but was marred by its clutch and transmission. The new engine with KIPS provided the highest power output in its class, and its sophisticated suspension offered adjustability akin to Jeff Ward's factory bike. Its mediocre cornering, soft suspension, and lack of low-end torque made it challenging for supercross track riding but still garnered a significant following. Even with its poor clutch, finicky gear shifting, and somewhat sloppy assembly, the Kawasaki remained a popular choice for many. The fast, futuristic, yet imperfect 1985 KX250 was a typical motocross machine of the mid-eighties.

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