Kawasaki Kx250-A4
KAWASAKI KX250-A4
A Limited Production Works Bike
CYCLE WORLD TEST
For the past few years we have watched the factory Kawasakis develop into competitive machines. Watch was all the public could do.
The only MXer available from the Big K was a model that was the same green color but had little else in common. The bikes had powerful motors but the handling left much to be desired.
For 1978 Kawasaki decided to öfter a limited production motocrosser to the public. This bike's serious nature shows when you look at the leading axle forks with cooling fins on the lower castings, the aluminum swing arm. hollow axles, hollow brake pivot shafts and generally lean, uncluttered look.
The Kawasaki is a real attention getter with its green and gold color scheme. The fenders, side plates and tank are Kawasaki’s familiar green. The swing arm. wheel rims and front engine mounting plates are nicely done in a gold finish.
The KX frame looks much like Suzuki’s with a less radical shock angle. A large diameter single front downtube is heavily gusseted at the steering head. Two smaller tubes spread under the engine, turn upward and forward to terminate at the main backbone tube just in front of the seat. An equal size tube starts behind the swing arm pivot bolt and goes up and rearward to connect to the seat rails. This effectively forms a triangle under the seat and adds to the frame rigidity. The main backbone is a large tube that runs from the steering head to seat rails. A smaller tube combined with large gussets forms a triangle to strengthen this area. More formed gusset plates are used below, above and on each side of the frame's steering head to help add strength there.
The steering stem rotates in first-rate tapered Timken bearings. Both crowns are made from forged aluminum and employ double pinch bolts. The bar mounts are aft of the stanchion tubes.
The aluminum swing arm is anodized an attractive gold color and has welds neatly done in a continuous flow. Aluminum arms are stock on many of the new MXers but none are as nicely executed as the Kawasaki.
We have never seen a motocrosser with so many hollow bolts. Many have dished bolt heads as well. Even the brake actuating cams have hollow shafts.
The brake pedal is an aluminum forging that has a height adjuster and pivots on a hollow, dished head bolt.
This kind of attention to weight saving is carried to the wheels as well. Both have magnesium backing plates and the rear hub (normally one of the worst weight offenders) is made from magnesium. Both hubs are conical in design and the rear brake is full-floating. The torque arm between the frame and rear backing plate uses needle bearings. Most bikes use rubber bushings for torque pivot arms.
Large spokes attach the nice hubs to lipless aluminum rims.
Like the rest of the machine, the engine has received special attention concerning> weight reduction. The cylinder has a special electrofusion cylinder lining process. Different types of metal are exploded into the aluminum cylinder wall to create a light, long-wearing surface. This process is claimed to be better than a chrome-plated aluminum cylinder. Sometimes the plating on chrome bores comes loose and peels. With the electrofusion process, peeling is impossible. Both processes save several pounds over conventional steel lined bores. Unfortunately both require cylinder replacement should anything come loose and gouge the surface. Without a steel liner the external cylinder size can also be reduced, further reducing weight.
A 38mm Mikuni carb feeds the fuel through a large Boyesen six-pedal reed valve. The piston uses two Dykes-type rings and has two large holes in the rear of its skirt to allow fuel to enter before the skirt uncovers the port.
A good plastic air filter box with a top air feed is furnished. The right side has a large opening to ease maintenance. This opening is covered by the right-side number plate.
The transmission is a 5-speed and everything internally has been built with attention to weight reduction.
The drive sprocket is quite a distance from the swing arm pivot so a chain tensioner is needed. Instead of using springloaded devices, Kawasaki wisely chose stationary plastic roller wheels, one below the swing arm pivot one above and to the rear of it. These control chains slop nicely. A well made chain guide is mounted in front of the rear sprocket and has rollers top and bottom. A rubber chain rubbing block is used on the front of the swing arm to keep the chain from sawing into it.
The forks on the KX are some of the neatest looking around. Cooling fins grace the lower fronts and rubber protects them to ward off rocks, etc. The oil seals and stanchion tubes are well protected with rubber accordian boots. They are leading axle air/oil units and have 9.3 in. of travel.
At the rear remote reservoir, KYB shocks allow a little more than 8 in. of wheel travel.
The KX is a narrowbike. The aluminum gas tank is one of the things that make it narrow. Unfortunately the tank doesn’t do much to enhance the appeal of the bike, being rather plain looking.
The rear fender also looks wrong. Although made from a good flexible plastic, it looks too short and has an odd
shape.The KX feels light and agile on a motocross track. The front end is very light and the front wheel can be lofted at about any speed.
The steering precision is almost as good as some of the European bikes. Tight lines in tricky places are almost easy with the KX.
Although the forks don’t offer as much total travel as some MXers, they perform well. Damping and spring weight was right for all the test riders.
The rear shocks are another thing though. They kicked and felt sticky. After a couple of days they loosened up and
worked much better. Although some fast lap times were turned, all the testers said they would replace the shocks with something else.
Most also complained about the touchy rear brake. It locked easily, it was an on-oroff, unprogressive feel. The front one worked fine, however.
Kawasaki has done an admirable job with their first publicly available, true motocrosser.
Once dialed in to personal preference parts like shocks and bars, the KX will be capable of winning almost any motocross event around. IS
KAWASAKI KX250-A4
SPECIFICATIONS
POWER TRANSMISSION
DIMENSIONS
FRONT FORKS
Kayaba leading-axle fork
At 9 in., travel on these KYB forks is adequate, but not exceptional. With the stock oil, damping was insufficient, however, and allowed the forks to bottom prematurely. An improvement in action was realized by using 10 wt. oil in lieu of the original.
REAR SHOCKS
Kayaba remote-reservoir shock
The KX’s rear end feels much too soft, a condition which is reflected in the very low spring and damping rates. Even with its mild 1.6:1 wheel-shock travel ratio, the 55-lb. primary spring rate was insufficient. A 65-70 lb. rate would be better. Rebound damping, at 56 lb., also is insufficient, causing rear-wheel kickback and instability. A set of accessory shocks is in order here.
