The Motorbike Archives

Well, Kawasaki now has a four-stroke playbike that changes all that. It's called the KLX250, and it measures four-stroke fun in a different way: cubic handling. And the KLX can manage such unprecedented behavior because Kawasaki did what no other manufacturer has done: build a four-stroke playbike by mating a slick motocross racing chassis with a medium-displacement thumper engine. And even though this particular example of that philosophy ended up vastly underpowered compared to its competition, it offers top-shelf handling the likes of which playbikes have never seen.

Beyond a doubt, it is the KLX's do-any-trick, take-any-bump handling that makes it one of the most fun-loving fool-around bikes you can get your hands on. Coupled, in fact, with the low-wattage engine, that handling can do wonders to boost the self-confidence and improve the riding skills of most less-experienced off-road riders. That's because there's seldom enough power available to push the chassis past its limits, which are quite high even by motocross standards. So without the need to worry about a magnum-force engine that can get him going too fast, too soon and too easily, the off-road neophyte can concentrate on learning how to control a bike in the dirt.

Whether the KLX's unremarkable power output is a plus or a minus, though, depends upon which side of the snow fence you spend most of your time behind. Experienced motocross racers, expert dirt riders and those who like their horsepower doled out in megadoses will be bored stiff before they ever snick the five-speed gearbox into top cog for the first time. Oh, sure, there's no peakiness at all to be found in the powerband, and the torque curve has a nice, flat profile that's ideal for a dirt bike. The problem is that the curve never gets very high between kick-starting speed and valve-float rpm.

But for the rider who has not yet adjusted to the peculiarities of rear-wheel spin and unavoidable tire-slip, for the guy who's happiest when both tires are on the ground, the KLX will be just what the dirt doctor ordered. That kind of rider won't care that the power pulses reaching the rear wheel are more like dull thuds than minor earthquakes. Instead he'll be tickled pink that none of those conventional four-stroke performance standards are relevant to this Kawasaki, that he can finally straddle a real off-road motorcycle that isn't intimidating but handles well enough to forgive his frequent mistakes. Tracing down the reasons for the meager power output leads directly to Kawasaki's decision to virtually transplant the 246cc engine from the KL250 street/ trail model into the KLX. There are, in fact, just three significant performance differences between the two engines: The KLX has a 32mm Mikuni carb rather than the 28mm mixer on the KL, and the former's valves, both intake and exhaust, are a millimeter larger. And to complement the marginally improved breathing, the KL's heavy and restrictive exhaust system was dumped in favor of a high pipe capped off by a smaller, lighter muffler.

An intelligent person has to wonder why more vitality wasn't pumped into the KLX's mini-thumper engine. The answer is simple: economics. The KLX was the brainchild of a few R&D people at Kawasaki Motor Corporation, the U.S. distributor of Green Meanies, who had pleaded with the factory for years to build some kind of four-stroke playbike. Finally, they got the notion to do it themselves by slipping a KL250 engine into a KX125 chassis. They tried it, they liked it, and they sent it to Japan with instructions to build it. Rather than invest any more precious time and money with further development, the decision was made to market the bike with what was already available, which meant using a minimally modified KL250 engine.

Kawasaki is fully aware of the horsepower shortage in the KLX and is currently developing a line of performance parts for it. Items such as a high-lift cam, stiffer valve springs, a big-bore kit and a stroked crank supposedly are in the works and will be sold as optional equipment.

Two other engine changes were made for the sake of reliability and service rather than performance. Of particular significance is a magnetically triggered CDI that replaces the breaker-point ignition used on the KL engine. And to make oil changes easier, the clutch cover was redesigned so that it doesn't have to be removed when changing the filter.

Stuffing the KL engine into the KX125 frame wasn't as difficult as one might imagine. The small-diameter frame tube below the main backbone was bent upward to accommodate the single-overhead-cam engine's height, and new motor mounts were required to mate the engine's mounting lugs to the KX's frame. Otherwise, the remainder of the chromoly KLX frame is the same as the 125's.

Not so the swingarm, however, for the gold-anodized aluminum rear fork used on the KX wasn't carried over to the KLX. In its place is a half-inch shorter arm like that used on Kawasaki's new KDX400 two-stroke enduro. The legs of this forged aluminum swingarm are I-beam in cross-section, helping to make it stronger than the KX's boxed unit and less expensive to manufacture. It also relocates the lower shock mounts slightly further forward, raising the seat height an inch, steepening the steering head angle by one degree and shortening the front wheel trail.

One KX125 swingarm component that did make it onto the KLX is the nylon drive-chain rubbing pad just above the swingarm pivot. But that's too bad, because the pad doesn't seem to last very long on this particular permutation. The problem may be caused by the large amount of chain slack that must be present when the suspension is at or near full extension. Whatever the reason, substituting the more rugged rubbing block from a KX250 motocrosser is, according to Kawasaki, an effective cure.

That unusual amount of free play exists because the long-travel KX chassis and the KL engine (from a medium-travel motorcycle) weren't designed for one another at the outset. Consequently, the countershaft sprocket and swingarm pivot couldn't be put close enough to one another to handle the chain-related effects of 10 inches of wheel travel. If it's properly tensioned when the axle, swingarm pivot and countershaft are in line (about midway in the travel), the chain will have excessive play at the extremes of travel. And although the KLX has two frame-mounted chain rollers to help the problem, they don't help enough.

That point was made crystal-clear during our testing when, within 30 miles of an adjustment, the chain stretched enough that it tried to ride up off of the countershaft sprocket teeth. As a result, the chain broke a small piece out of the engine case and bent the clutch pushrod, which is positioned very close to the front of the sprocket, allowing engine oil to leak past the pushrod seal. The moral: Don't let your KLX's chain get very loose, or else use the next-smallest countershaft sprocket so that the chain does not run so dangerously close to the clutch pushrod.

One other reliability concern emerging from the KL250/KX125 synergy is that the 239-pound KLX has the very same small-gauge spokes as used on the sub200-pound KX. Moreover, the average 125-class rider undoubtedly is 25 to 50 pounds lighter than the person you would expect to find on a KLX. So if Kawasaki's mini thumper is ridden hard on rough ground, frequent spoke maintenance could become a way of life.

Somehow, though, those problems don't seem to matter while you're riding the KLX. You're usually too busy having the time of your life playing around with this little jewel to worry about undersized spokes or too-slack chains. The KLX lets you get away with stunts that would be the downfall of other thumpers. It handles and steers with all the grace and precision of a motocross bike.

Actually, the KLX always steers at least as well as the KX125 and sometimes even better. Part of this is owed to the quickened steering geometry, part to the shortened wheelbase. But the addition of a four-stroke engine must be credited, too, for its higher and greater mass provides better weight transfer onto the front wheel when braking or slowing for a turn. The added compression braking of the four-stroke further benefits the KLX's turning prowess, for closing the throttle helps induce a rear-wheel drift into turns. On the other hand, the KLX has trouble drifting the rear wheel when coming out of turns because of the engine's low voltage. And while that particular characteristic might even be considered a blessing by some, few people will have much affection for the way the engine pushes the KLX up hills—or, in some cases, the way it doesn't. First and second gear are low enough to let you churn up most short, slow hills; but if you come to one of those long upgrades that call for a quick burst of momentum-gathering speed at the bottom, forget it. And even if, by sheer talent alone, you happen to get going fast enough by the time you hit the seriously steep parts, don't make any mistakes. Because if you lose the slightest bit of momentum along the way, you probably won't reach the top.

While that horsepower deficit might turn off hardened, experienced off-roaders, most struggling dirt novices will welcome it like money from home. If there's a weakness in that first line of low-horse defense, though, it's that with a bike of the KLX's handling benevolence, struggling dirt novices won't stay that way very long. Sooner or later—most likely sooner, in this case—even they will yearn for more power. It doesn't take long to grow impatient with the KLX's lazy acceleration, regardless of riding skills.

Compared to the weight and handling shortcomings of other thumpers, though, the KLX's problem isn't such a bad deal. Hopping up four-stroke engines is a much more clearly understood craft than the science of dirt-bike handling. It's much easier and cheaper—and usually more fruitful—to make a slow engine faster than it is to turn a mediocre chassis into a nimble handler. So between Kawasaki's planned optional performance gear and the plethora of aftermarket equipment that the KLX is already generating, more power is on the way.

Horsepower or no horsepower, though, the KLX is a portent of things to come, a prototypal playbike of the Eighties, if you will. You're going to see more motorcycles like the KLX. Whether they'll be CR125 Hondas with XR250 engines or RM125 Suzukis with DR370 singles in their midst is hard to say, but you'll see them nonetheless. And they'll follow the same basic KLX formula: a world-class chassis with some form of thump-thumpa propulsion.►