The Motorbike Archives

The staff at CYCLE GUIDE feels just that way about the motorcycles we test. Sometimes the styling and often the performance of a bike don't quite meet up with our idea of perfection. And just like you, we set about dialing in the changes we think will help. We might not achieve perfection, but any of these projects is declared successful if the bike ends up better than stock, which is not always the case.

The Kawasaki KX420 was a prime candidate for such a project. And it is the first of many that we will try to improve in the pages of CYCLE GUIDE. Sometimes changes will be made in the interests of fashion, but, as in the case of the Kawasaki, most of our tinkering will be done to create a better-performing motorcycle.

Kawasaki's KX420 seemed ripe for some tinkering because it showed such promise yet de- livered so little. The new Uni-Trak suspension was potentially the most sophisticated moto- cross rear end that money could buy. And the 420 motor, too, held the promise of being a motocross star. Neither was the case, however, when Green Meanie and brown berms met.

Much of the KX's faults lay in the rear suspension, which was a major problem simply because it was so stiff. Both spring and damper rates seemed inordinately high, even when both were on the softest settings. It was a case of factory miscalculation that even Kawasaki's accessory spring could not completely cure.

Kawasaki dealers around the country do have one answer to the KX suspension woes, even though Kawasaki doesn't advertise it. A KX250 chassis is identical to the 420's, yet the 250 has a much lighter spring and damping rate. The 250's shock itself is completely different, but it bolts right in place on the Open- classer as if it belonged there.

Installation poses the usual problems of having to remove the air box, but once the shock is in place everything fits perfectly. Our first set- tins had spring preload in the middle position, as was the rebound damping. There was still no sag when we sat on the seat, but on the track the improvement was immediately noticeable. But still not perfect; both a 165-pound and 190- pound rider wanted less spring and more damping.

With preload backed off to zero and damping set in the hardest of four positions we came as close as we were going to get to perfection. We were still some way away, but it was a considerable improvement. However, the shock change did not stop the front end pushing in turns or make us quite as relaxed as some other Open- classers do. But for the time being the suspension tinkering is stalled for lack of other after- market shocks for the 420.

There are also very few bolt-on parts for the 420 motor. And it really could do with some help. The standard motor, despite displacing 420cc, has the power band of a 250. The horsepower graph looks more like a closeup of a darning needle, with sheer sides rising to a pointed peak at 7000 rpm.

That might be acceptable if there were lent of peak power to use, but there is not. p

Hacking extra power from the electrofusion- coated barrel is not an easy solution, but broadening the power is. By adding extra flywheel weight the 420 can be ridden more easily even if it is not more powerful.

Again Kawasaki dealers are stocking one answer. If you look in their parts book, you find that a KDX400 Enduro crank is identical to a KX420's, apart from the ignition side taper. That is where the large outer rotor enduro mag sits. The KX rotor weighs a skinny 1.2 lbs, but the KDX flywheel adds a massive 200 percent more weight on top of that.

Installation obviously requires a complete motor teardown along with new seals and bearings, but the job is quite straightforward. And when the new ignition is hooked up to the enduro black box you are ready to roll.

Just like the rear suspension changes, the heavier crank makes a noticeable difference. From the first ride we liked the change, enjoy- in g a more predictable power delivery. Power still comes on strong at high rpm, but it now comes with the surge of an Open-classer rather than the explosion of a 125. Living with the 420 motor is easier, but it still lacks the sheer horsepower numbers to blow the opposition away. So, like the suspension changes, it is a short step in the right direction.

The modifications aren't cheap—a crank and ignition cost $286.05 and a shock and spring hit you for $255.00, but they go a' long way toward perfecting the KX. Not all the way, of course, since few changes ever do create perfection. But for most riders they can produce something that's better than stock.■