Stroker's KLX 300 Stage 1 Mods

When Kawasaki introduced their new KLX 300 off-road machine to the world, we sang nothing but its praises. Hail to the suspension! Hail to the dual overhead-cam four-stroke powerplant! Hail to its 231.5 pound dry weight! Hail! Hail! Hail!

Alas, as in life, nothing's perfect. In human terms the KLX suffers from a minor case of constipation and a touch of asthma. Technically speaking, both the Kawasaki's intake and exhaust systems are somewhat restricted. Fortunately, there is a doctor in the house.

Stroker Inc., based out of California, offers a full range of engine, suspension, performance parts and modifications for Kawasaki's KLX. Racing legend Larry Roeseler founded the company after working very closely with Kawasaki's off-road race team.

Stroker won't just try to sell you parts. The company has a great deal of experience setting up bikes for a variety of riders and situations. When you call you'll most likely reach Larry himself. Tell him you're a great fan, what kind of rider you are and what you are trying to accomplish, and he'll provide a common sense solution.

We complained to Roeseler about the KLX's lack of throttle response. He told us we would need a new carburetor, throttle and exhaust pipe. Roeseler states the problem is that Kawasaki fitted a CV carb on the KLX. Constant velocity carburetors are common in street bike applications where they produce smooth acceleration and reduce engine bog. CV's prevent an engine from being fed more fuel than it can handle.

With a CV carb, the speed at which its slide opens is dependent more on engine vacuum than physical throttle response or position. Whack the throttle open or roll it on quickly and the slide will open only as fast as engine vacuum builds. When riding off-road, if you need a burst of power to blip over an obstacle or steer through a wash, you'll need to anticipate what you want from the motor well in advance, not to mention using the clutch more than usual.

Stroker sent us a pipe, carb, and throttle. Here's what we did. Remove the stock air filter and replace it with a KX 500 part. It's larger and will flow more air. Stroker recommends against using the airbox lid, but since we've been doing a bit of wet weather riding, we choose instead to modify the lid to allow more air flow. We simply made rectangular cuts in the box lid and used heat glue to fasten nylon mesh where plastic had been.

The push-pull, full-turn throttle fitted as stock on the KLX is a carpal tunnel sufferer's nightmare. Stroker sent us a Motion Pro "CR Pro" throttle complete with a custom cable made for the KLX. Once in, just a quarter turn and the KLX will deliver full power. This modification is a must even if you choose not to buy a pipe or carburetor. It takes some getting used to, but is well worth learning.

Next, remove the stock exhaust header pipe and compare it to the Stroker unit. It's okay to "ooh" then "aah." The Stroker pipe is much larger and reeks of horsepower. Remove the gas tank and radiator shrouds and you are ready to replace the carb. Roeseler provided us with a Mikuni TM33-8012 flat slide unit with the following base settings:

Main jet - 142.5 
Pilot jet - 45 
Needle - 3rd clip 
Fuel screw - 1 turn out
The carb kit comes with good instructions, but we made some alterations to save time and energy. Fitting the carburetor requires you to modify the cylinder head-stay. Rather than cut away material from the head-stay as instructed, we cut the welded nuts from the head-stay bracket and doubled up the brackets on the left side of the stay, leaving no bracket on the right side. This method leaves more room for installation, but we have yet to determine if it will cause any problems with use.

In order for the gas tank to clear the top of the carb it must be raised. We glued a 1/4-inch piece of rubber to the existing rubber mount using Goop liquid adhesive. Seat installation or fit is not compromised in any way.

As simple as it is, the Stroker head pipe is a work of art. Sporting more girth and less divergent bends than the stock unit, it's clear what it was designed to do -- flow plenty of exhaust. Larry tells us the stock head pipe is actually the same unit as used on Kawasaki's KLX 250. It has abrupt internal welds and its inlet face does not mate well with the exhaust port. But he claims the stock silencer works quite well and did not feel it was worth using a substitute at this time. Our Stroker pipe fit without much more effort than a few light taps from a rubber mallet. However, you won't be able to use the stock clamp to mount the silencer unless you modify it. We opted for a heavy-duty hose clamp.

The combined changes we've made have transformed our bike into a more rideable machine at minimal cost and effort. Our KLX accelerates much harder at all speeds, no longer lags off idle and requires far less work to ride. Initially, the jetting specs above were too rich for riding in the Northeast U.S., but dropping the needle one position cleaned up responsiveness and stopped the occasional backfiring we experienced in chop-throttle situations.

Stroker's carb kit, which includes the throttle and cable, retails for $325. The exhaust header is $140. The cost, installation time and effort are well worth the trouble.

You can grab these goodies through Stroker Inc.
11114 "G" Avenue #2
Hesperia, CA 92345

Get in your Inbox