For this edition of Classic Steel, we are going to take a look back at Kawasaki’s revamped 1991 KX125.
After setting the moto world on fire in 1990 with a radical redesign, the KX125 was back in 1991 with a more conservative list of updates and improvements. Photo Credit: Kawasaki
In 1990, Kawasaki blew back the wigs of the moto press with the introduction of their all-new perimeter-framed KX125. Where previous KX125s had been conservative and competent, this new version of the green machine was radically styled, aggressive in performance, and innovative in design. With its road race-inspired perimeter frame, plug-in fuel cell, and detachable alloy shock tower, the 1990 Kawasaki KX125 was unlike any other 125 on the track.
In 1990, Kawasaki pointed the way forward by bringing a twin-spar perimeter frame design to the motocross world. While admirably stout, this first version was heavy, tall, and wide, giving the KX a heftier feel than some riders appreciated. Photo Credit: Kawasaki
After several years of milk toast KX125s, this spicy new version proved a tremendous hit with consumers. Riders loved its spacy looks, potent power, and innovative construction and snapped up the green tiddlers in droves. For the first time in years, Kawasakis were cool again as a sea of green made their way to local tracks everywhere.
All-new Kayaba forks for 1991 increased the size of the stanchions by 2mm and added a love-it or hate-it blue hue. Photo Credit: Kawasaki
While the 1990 KX125 proved a tremendous success on the sales floor, it was not without its share of complaints. For the most part, these centered around its peaky powerband, slightly quirky handling, and plus-sized feel. Unlike the previous three years of KX125s, the 1990 version eschewed a broad powerband in favor of lots of midrange hit that rocketed the KX out of turns. There was virtually no bottom-end power to fall back on, however, and the KX’s potent motor could be difficult for less-skilled riders to use effectively.
Motor changes for 1991 included an all-new cylinder, head, piston, and beefed-up crank. Photo Credit: Kawasaki
On the chassis front, the move to the perimeter frame delivered advantages and disadvantages. In the showroom, it looked trick, and on the track, it was incredibly stout, but its wide frame spars and tall layout made the KX125 feel less wieldy than its 125 competition. The bike turned well in most circumstances, but it felt tall in the front, short in the back, and much larger than its rivals. This gave the bike a unique feel at turn-in that not everyone liked, and it could be a bit twitchy at speed. The new inverted forks and redesigned Uni-Trak worked well in most situations, but more than a few riders lamented the reduced plushness they exhibited compared to the ultra-smooth 1989 components. Overall, however, the 1990 KX125 proved a tremendous success both on and off the track.
A revised Uni-Trak linkage for 1991 added a more progressive curve for smoother performance. Photo Credit: Kawasaki
For 1991, Kawasaki aimed to keep that momentum going by broadening the power and improving the suspension of their ultra-trick tiddler. As in 1990, the KX’s powerplant remained a liquid-cooled case-reed design displacing 124cc. Bore and stroke were unchanged at 56mm x 50.6mm and the new motor retained the Kawasaki Integrated Power-valve System (KIPS) in use since 1985. To broaden the power for 1991, Kawasaki dialed up an all-new top end a new microprocessor-controlled digital ignition. The cylinder, head, and piston were all new with revised porting, a reshaped combustion chamber, and a move to a flat-top design for the piston. The high-tech ignition offered all-new programming designed to provide improved combustion and increased throttle response at low RPM. The flywheel weight was increased slightly for 1991 to provide a smoother delivery and increased tractability. In a nod to durability, the big end bearing was upgraded for 1991 and the revamped piston featured a thicker ring than in 1990. The water pump was also improved in 1991 to be lighter and offer enhanced flow to the dual radiators.
Frame geometry remained unchanged for 1991, but Kawasaki added additional bracing to the steering head and rear swingarm to fine-tune the KX’s handling. Photo Credit: Kawasaki
On the intake side the 1991 KX125 continued to employ Keihin’s proven 35mm TMX mixer and a six-petal carbon fiber reed valve. An all-new exhaust maintained the “low boy” layout of 1990 but added revised dimensions designed to boost low-to-mid power. The silencer was a carryover from 1990 with a trick look and lightweight alloy construction.
All-new wheels for 1991 reduced weight and revamped brakes increased bite at the lever. Photo Credit: Kawasaki
On the chassis front, the KX125 retained the unique perimeter construction it had introduced in 1990. Improvements for 1991 included a beefed-up steering head and a lightened alloy subframe. The frame retained the high tensile steel box section construction it employed in 1990 and maintained the same geometry as the year before. A redesigned swingarm added a revised Uni-Trak linkage and additional bracing with a new one-piece cast-alloy cross brace. Lighter wheels for 1991shaved a few ounces off the chassis and a revamped dual-piston front caliper with sintered metal pads added additional stopping power.
The KX’s unique perimeter frame was super trick, but its design made it difficult to add a larger tank without significantly impacting the machine’s ergonomics. While few KX125s probably made it to the desert, many KX250 owners found they were forced to make some tough comfort decisions when faced with increasing the stock machine’s 2.25-gallon capacity. Photo Credit: Kawasaki
On the suspension front, the KX125 was upgraded both front and rear in 1991. In the front, Kawasaki upsized the forks 2mm, moved to thinner-walled tubes, and anodized them blue. The new 43mm Kayaba inverted forks featured revised damping, reduced weight, and increased rigidity for 1991. Both compression and rebound damping were externally adjustable with sixteen selectable settings available and 12.2” of travel.
In 1991, former 125 National Motocross champion Mike Kiedrowski made the jump to Kawasaki after two very successful years at Honda. Indoors, Mike would campaign his KX250 to fourth overall in the series. Outdoors, the MX Kied would step back down to the 125 class and put his KX125 at the front of a very competitive pack of young talent and established veterans. Photo Credit: Motocross Action
In the rear, the KX featured an all-new lever ratio for 1991 designed to provide a more progressive action. The Kayaba shock was largely a carryover from 1990 but Kawasaki did add new valving and a slightly softer spring designed to work with the revamped Uni-Trak. Compression and rebound damping offered sixteen-way external adjustability with 13” of travel available.
The motor changes for 1991 broadened the KX’s power at the expense of some of the 1990 model’s excitement. There was more low-end torque available but less of the mid-range hit that pleased throttle jockeys the year before. Both motors were very competitive, but the 1991 version was easier to ride and more appealing to less-skilled pilots. Photo Credit: Kawasaki
On the track, the 1991 KX125 proved to be an upgrade in most respects over the popular 1990 machine. Most noticeable of the changes was the new powerband which proved much easier to harness than the year before. Where the 1990 version was listless down low, berserk in the middle, and howling on top, this new version picked up sooner, hit a bit less hard in the middle, and still pulled well on top. The improved low end and mellowed midrange hit made the bike feel a bit slower to many, but the motor was far less likely to fall off the pipe between gears, easier to get hooked up, and more effective in most situations.
Red Rocket: In the horsepower derby of 1991 there was one machine that stood head and shoulders above the rest of its 125 competitors. Honda’s CR125R pulled harder and farther than any other machine in the class but its raw power advantage came at the expense of usability. Its motor was a mid-and-up screamer that came on late and tended to fall off the pipe if not pinned to the stops. For many riders, the instant power of the RM125 and broad delivery of the KX125 were preferable to the peaky Honda. At the bottom of the power rankings for 1991 was the YZ125, which struggled to keep up with any of the Big Four competitors without serious motor work being done. Photo Credit: Dirt Bike
The additional torque down low pleased riders who had struggled with the potent but peaky 1990 powerband, but some fast guys lamented the trade of midrange bark for a beefed-up low end they would never need or use. They felt the new powerband was a step back from the exciting 1990 version, but this was far from the majority opinion. Both motors were very fast and competitive, but one was just a bit more user-friendly than the other. Despite its smoother delivery, the KX remained one of the fastest machines in the class in 1991. It was less powerful on top than the high-strung Honda and not as “right now” responsive as the snappy RM125, but to many, it offered the best combination of power and ease of use in the class.
The KX’s wide and tall frame and oversized ergonomics made it feel less nimble than some of its competitors, but it was far from a poor handler. Front-end traction was good, and the bike was stable at speed. Once you got used to the size, the KX offered one of the best all-around handling packages in the 1991 125 class. Photo Credit: Motocross Action
On the suspension front, the KX was more unanimously praised for 1991. The new blue 43mm KYB forks were far plusher than in 1990 and universally loved for their smooth and well-sorted action. Braking bumps, small chop, and hard curbs that pounded the wrists of riders on the Honda were gobbled up with glee on the KX. It brought back the plushness of the ’89 KX’s fork while still offering admirable resistance to bottoming and excellent control. Riders of all skill levels praised their action, and it was easily rated the best front end of 1991.
The all-new 43mm Kayaba forks on the KX125 were well sprung, expertly damped, and some of the best silverware available in the 1991 125 class. Plush and well-controlled, they gave the KX’s pilot a significant advantage once the track got rough. Photo Credit: Kawasaki
In the rear, the KX125 was nearly as universally praised as the front. The revamped KYB damper was slightly firm in action to some, but this balanced out the chassis better than in 1990. This firmer feel was still excellent at absorbing most track obstacles and the KX could be charged into whoops and launched into the stratosphere without any fear of the shock slamming to the stops or kicking you out of the saddle. It offered a great combination of comfort and control, and most riders could find a raceable setting by dialing in the available adjustments. Overall, an excellent rear damper.
Despite its large feel, the KX125 was a good flier. Photo Credit: Tom Webb
As in 1990, the most controversial aspect of the KX was once again its size. The move to the perimeter frame “plus sized” the KX125 in every dimension and this gave the machine a very different feel than its rivals. The front of the bike was very wide and tall, and its handling feel was less precise when the track was tight. It did not really turn badly, it just felt more unwieldy than carvers like the CR and RM. Front-end traction was good, but the KX “fell” into turns rather than flowing through them. Being a 125, it was still far easier to throw around than a KX500, but the differences in feel when switching from another brand to the Kawasaki were noticeable.
Like the forks, rear shock action was excellent and the KX offered the best overall suspension package in the class. Photo Credit: Kawasaki
Without a major change to the chassis, this “big bike” feel was not going to go away, but Kawasaki did make some improvements in handling for 1991. The beefier forks, better-balanced suspension, and braced-up frame yielded excellent front-end traction and much better stability. The bike still felt big, tall, and wide, but the front end stuck to the track and went where it was pointed. At speed, the KX was never a shaker like the RM and CR, but it had been a bit busy in 1990. For 1991, this meandering was greatly lessened, and the bike felt far more planted when the speeds ramped up. Jumping the KX was a no-drama affair, and the bike flew well and landed with confidence. It was the heaviest 125 at 208 pounds and its larger size made it feel less flickable than the feathery RM, but it was still a 125 and no one was going to confuse it for an XR600R.
With its strong motor, excellent suspension, and stout chassis, the KX125 was a really fun bike to ride in 1991. Photo Credit: Dirt Bike
The Champ: Mike Kiedrowski took his talents to Kawasaki and delivered the green team its first 125 National Motocross title since Jeff Ward in 1984. Photo Credit: Motocross Action
On the detailing front, the KX was a bit of a mixed bag in 1991. Most riders praised the KX’s looks and the bike that looked so avant-garde in 1990 seemed positively conservative when placed next to the Rorschach test graphics emblazoned on the KX’s 1991 rivals. Tiger stripes, check marks, cat barf graphics, and crazy color pallet swaps all tried to capture some of the excitement generated by the KX’s looks in 1990. Compared to these graphical Hail Marys, the KX’s blue forks and subtle graphical updates were positively low-key. The only controversial change to the KX’s appearance for 1991 was those blue forks, which some riders thought were a bit passé and tended to fade over time. Blue forks or not, however, the KX125 remained one of the best-looking machines in the 125 class.
There seems to have been a good deal of disagreement in 1991 over who made the best 125 available. Motocross Action felt the KX deserved the crown for its overall excellence, while Dirt Rider fell in love with the RM’s snappy power and razor-sharp manners. Everyone agreed that the Honda was fastest but only Dirt Bike could turn a blind eye to its utter lack of suspension comfort. In the end, everyone but the Yamaha had their devotees, and you could certainly win on any of the four machines with a bit of skill and fine-tuning. Photo Credit: Dirt Bike
One of the keys to the KX’s cool appearance was its trick perimeter frame, which continued to prove very stout, but its unique bolt-on alloy shock tower remained a point of some concern. Hard-ridden KXs suffered from cracks in this area, and it was advisable to check for stress fractures regularly. The KX’s massive pegs were loved by all for their comfort, but they tended to droop over time and break return springs at a surprising clip. Always keeping a few spare springs in the toolbox was a solid plan. The KX’s gas cap was also of suspect quality, and it tended to leak if not cinched down tightly and crack if torqued too aggressively. Finding this middle ground between no leak and no crack was a bit of alchemy long-time KX riders acquired. The minimalist fork guards looked factory-trick, but they offered marginal protection and were easily damaged when subjected to contact. The more comprehensive coverage offered on the Honda, Yamaha, and KTM were superior in protection and far more durable in the heat of battle. Most of the other plastic was of good quality and less brittle than older KXs, which tended to crack more than the competition. The seat was wide and comfortable, but the stock cover seemed very thin, and many riders found it prone to tearing at the front corner. Graphical life was good, however, and the stock decals lasted long enough to make your first payment.
You can thank Kawasaki for making skinny footpegs a thing of the past. These massive floorboards were twice the size of anyone else’s pegs in 1991. Photo Credit: Kawasaki
The KX’s motor proved reliable and ran well once the jetting was dialed. The trick shutter built into the airbox allowed for increased air on clear days and reduced water intake if it was a mudder. The clutch and transmission worked well and the KX straddled the middle ground between the ultra-slick CR and RM combos and cranky YZ and KTM. The stock steel bars looked cool in green, but no one liked the bend, and they proved even less durable than the auto-ejecting footpeg return springs. The stock gearing worked well for most riders, but slower pilots benefited from an additional tooth on the rear to help the KX get into the meat of its power sooner. The stock chain and sprockets were garbage anyway so an upgrade in this area was nearly mandatory. The selection and quality of fasteners were far inferior to the Honda but on par with the recycled tin found on the other Big Four rivals. The bolts and sizes were uniform, but they tended to come loose quite often, and it was a good idea to check everything before every ride.
Kawasaki’s trick airbox shutter was a great idea that went out of fashion for some reason. On a nice day, open it up and let in more air and if the skies turn gray, just spin it closed to seal things up. Photo Credit: Kawasaki
Braking performance was strong, but the KX’s brakes needed to be bled frequently to maintain their performance. This was in direct contrast to the Honda’s brakes, which never seemed to require any attention. Larger riders appreciated the KX’s roomy ergonomics and substantial feel, but kids coming off 80s could find its upsized dimensions intimidating. The bike was quite tall and noticeably wider and heavier than its rivals, which put off some riders. Most pilots got used to the KX’s unique proportions, but its plus-sized feel never fully went away.
Turn down for what: The turned-down exhaust tip is an iconic bit of 1990s moto that came in with the advent of the “low boy” exhaust and went out with the ridiculous overregulating of the FIM. Of all the sharp, spinning, and red-hot parts on a motocross bike, this is the one they chose to crucify into oblivion. Fully enclosed tips may be 10% safer but they will never be as cool. Photo Credit: Kawasaki
Overall, the 1991 Kawasaki KX125 proved to be a solid follow-up to the popular 1990 KX125. Improved power, suspension, and handling beefed up an already solid 125 package. Really fast guys shrugged at the improved low-end and lamented the mellowed hit, but for most pilots, the wider 1991 powerband was an improvement. It was not quite as fast as the CR and not quite as snappy as the RM, but to many, it offered the best combination of power and responsiveness in the class. The inherent compromises of the KX’s unique chassis meant it was not going to be a perfect fit for everyone, but it offered more than enough performance to win. If you could live with a bit larger dance partner, then the KX125 was an excellent place to start collecting trophies in 1991.
The Kawasaki’s revamped KX125 had a lot to offer in 1991. Sano looks, a potent motor, dialed suspension, and solid handling highlighted one of the best all-around racing packages of the year. Photo Credit: Kawasaki
