Kawasaki Klx300
KAWASAKI KLX300
CW PROJECT
CARRIED AWAY WITH KLX-CESS
BIG-BORE KITS, STROKER CRANKS, BIGGER carbs, ported heads, larger valves, cams this and cams that...and this is only the motor. Everybody in the aftermarket industry seems to have something for the Kawasaki KLX250.It has to be the dirt hop-up bike of the year—and it was already great in stock form. But why not make great even better? The liquid-cooled KLX mini-Thumper has proved its worth in more ways than one. It's done well in competition, while also pleasing almost every trailrider who has thrown a leg over it. Spend any time on a KLX, and you get the feeling you're on of the one best-handling bikes around-because you are. The KLX is fast becoming the option for riders looking for a four-stroke that's lighter than a Honda XR600 and has less girth than a Suzuki DR350. Of course, there's a limit to how much oomph 250 cubic centimeters of four-stroke power can give, which leads us to our Project KLX300.
KLX250 owners we talked to have all experienced significant gains with carb swaps. The most successful unit being the Mikuni TM33 pumper off a DR350. This slides right into the KLX manifold and airbox boot, requiring only a small amount of grinding to remove the corner of a frame tab for clearance. The push side of the pushpull arm has to be removed and then hooked to a custom Motion Pro single-pull throttle and cable.
Our final jetting for the Mikuni was a #145 main,
#35 pilot and air screw at one-and-a-half turns out.
Throttle response is improved tenfold. The lag of the stock, constant-velocity carburetor is replaced with instantaneous boost. You can now pull the front wheel up with just a twist of the wrist, no clutching necessary. Well worth the $275 retail price, the carb can be obtained from White Brothers or through any Mikuni dealer.
The carb was a nice addition, but we wanted more. Cycle Gear sells a 292cc big-bore kit for the KLX, complete with bored and Ni-Chromed cylinder and 78mm Wiseco piston. The California company has cylinders in stock and exchanges them on a core-charge basis.
Installing the 292cc kit is quite simple, provided you have a working knowledge of four-stroke motors: Just take out the stock parts and install the Cycle Gear counterparts. It’s almost as easy as it sounds. Base and head gaskets are included with the kit as is the Wiseco piston, rings, pin and circlips. After initial running-in, we bumped the main-jet size to a #150, and were ready to roost.
The kit’s increased displacement adds plenty of pull to the bottom end of the KLX’s powerband-very useful whether you’re a Novice or Expert. There’s definitely more power everywhere, way more on the bottom.
Searching for even more urge, we removed the airbox lid and pulled the baffle out of the stock exhaust system, but were annoyed at the resulting bark. We found out about an FMF muffler with a prototype baffle, and procured one to see if it reduced the noise. Success! Acceptably quiet while retaining the power of the baffleless stock muffler. The bad part is that as of presstime the FMF baffle remains a prototype, unavailable to the public. Hopefully, the aftermarket will respond to the demand for performance-oriented mufflers that are also quiet in the near future.
Now that we were completely satisfied with our motor, we looked at the suspension, already excellent in stock trim. The hot scoop was to slightly lengthen both ends and stiffen up the spring rates a bit to keep the footpegs higher off the ground-nothing drastic. Scotts Performance did the work, yielding an extra quarter-inch of travel out of both ends. Scotts custom valves the suspension for each individual rider, depending on size and ability.
We rid the bike of its wimpy stock chain in favor of a Tsubaki Omega O-ring chain spinning Sunstar Works Triplestar Sprockets. Next to be ash-canned were the flapping stock handguards; Acerbis Rally Handguards replaced those, joined by an Acerbis plastic fender brace and 3.7-gallon tank for those long-distance hauls. Long-wearing Metzeier MCE tires were used front and rear.
To round out the package, we went to Ceet for a seatcover treatment and the flame graphics on the stock radiator shrouds. Ceet also supplies optional stiffer foam for the KLX seat. As a final touch, we used aircraft-spec paint remover to give the radiators and swingarm that factory unfinished-aluminum look.
One of the biggest advantages to our KLX300 is the consistent starting and steady idle the pumper carb yields. We just had to be careful, as with all pumper carbs, not to twist the throttle while the bike was not running-that seriously floods the engine. One concern that we couldn’t address was the lack of a manual compression release. The stock automatic compression release is good for starting under normal circumstances, but if the bike gets flooded, then it is difficult to clean out, especially since it takes a little more might to kick over the 292cc kit.
Shifting was another bug that surfaced as the power output grew. Stock, the KLX tranny is a bit notchy, but never posed a problem. After the engine modifications, we encountered some false neutrals, especially downshifting. Cycle Gear has a mod for the KLX shifting star that reportedly cures this.
We loved our KLX as a stock bike, and after building the project bike, we came to appreciate it even more. All of its good qualities only got better, making the KLX300 a much more capable machine, whether playriding or enduro time-keeping. The problem is when you take a $5000 bike and bolt on $2000 worth of hop-ups, yes, that’s $7000. Seven grand is a lot for any bike, let alone a 300 four-stroke.
But if you’re a four-stoke fan who wants more power than a 250 without paying the weight penalty that a 600class Thumper brings, building-up bikes like the KLX250 will have to suffice-at a price. Still, any part of this KLX project-carb replacement, big-bore kit, suspension mods-will stand alone in boosting the KLX’s performance. Just pick your weak spot and upgrade. □
