Jump to content

Basic Mods for your KLX300


This article covers checking your carb needle to find out which one you have, and doing some basic mods to your KLX300 for quick and cheap performance gains.

Before I say anything else, I have to tell you that according to the Owner's manual for the 2006 KLX300, it is a federal offense to remove or modify any part of the intake system, carburetion system, or exhaust system. It is also a federal offense to operate any vehicle that has been modified in this manner.

Not only that, but making these modifications will void your warranty. Your dealer may charge you for repairs related to these systems if you modify them.

Having said all of that, everyone does it, and the dealers even tell people to do it. I've never heard of anyone getting busted anywhere but California for moding their bike.

Here's the deal:

In models previous to 2006, Kawasaki shipped the bike to 49 of the states with one type of needle in it. The California models got bikes with a different needle in them (and a bunch of other smog equipment). I don't know what the CA guys do to make their bikes run better.

The rest of the world, however, made some very easy mods to greatly improve the bike's performance:

a. Remove the airbox lid.

b. Replace the air filter

c. Remove the restrictor plate from the muffler.

d. Replace the crankcase breather hose.

Those changes, by themselves, made a huge difference.

However, starting with 2006, Kawasaki is shipping all U.S. bikes with the needle that they used to send only in the California bikes. Now, the Canada bikes get the good needle and everyone else gets the "bad" needle. With the bad needle in there, removing the airbox lid causes the bike to run like crap. So, now you need to replace that needle AND do all of the things mentioned above.

Here it is in more detail:

1. Identify your needle.

The first thing you need to do is find out what needle you have in there. To get to it, first remove the seat and gas tank (make sure you shut the gas off first). From there, you'll be able to get into the top of the carb, where the needle is. Here's an exploded diagram of the carburetor:


Make sure that when you take it apart, you carefully keep track of each component and put it back the way you found it.

The first thing to do is remove the diaphragm cover. That's #14041 in the picture. When it comes off, the spring under it will try to escape. Don't let it.

Get yourself a tupperware container and put the cover, screws, and spring in it.

Once you have the cover and spring out, stick your finger down the hole and gently remove the slide. Make sure the rubber diaphragm doesn't get stuck on anything and tear.

Once you have the slide out, put your hand over the hole and turn it upside down. The "seat-spring valve" (white plastic thing with legs, #16007) will come out, along with the needle possibly some other tiny bits like a collar (#92143) and spring clip (#92037) - but the clip, if it exists, should be firmly attached to the needle.

Compare your needle to these two pictures:

Needle2.jpg Needle3.jpg

If it looks like Needle2.jpg, it's the "bad" needle.

If it looks like Needle3.jpg, it's the "good" needle.

The needles also have little letters and numbers stamped into them near the fat end. If it says "N5AF", it's the "bad" needle. If it says "N1TC" it's the "good" needle.

If it is the good needle, put your bike back together and skip to step #2. Make sure you get that white plastic thing with leg in right. Don't cover the hole in the bottom; make sure it seats all of the way. Your bike will tell you if you get it wrong.

If it is the bad needle, call your dealer and order these parts:

16009-1912 - Needle-Jet,N1TC

92037-1401 - Clamp, Jet Needle

92143-1667 - Collar

The new needle will cost you about $20. Not sure about the clamp and collar, but they'll be cheap.

2. Remove the airbox lid.

This step is frighteningly easy. Just pull off the seat, unscrew the four bolts holding the lid on, pull it off (and store it safely somewhere), and put the screws back in. I recommend this so that you don't lose the screws, and so that your screw holes don't get muddy, corroded, or whatever.

The airbox lid looks like this:


See how small the intake holes are in that lid? See how much more air it can get if you remove it?

Oh, and by the way, see how much more dust, grit, sand, and water can get into the airbox without the lid? Clean and lube your air filter VERY often after you've taken that lid off. Get some air filter oil and remover that is easy to clean off and re-apply. I recommend "No-Toil" filter oil and cleaner. No-Toil also sells filters, but the popular opinion says to buy a "UNI" filter instead. It has a rough outer filter and fine inner filter. It lets more air in while still filtering out the bad stuff. They cost about $20. The No-Toil costs about $7.95 each for the oil and cleaner.

3. Remove the restrictor plate.

This is also very easy. The plate at the back of the muffler has two screws holding it on. Remove them, remove the plate, store the plate with the airbox lid, and put the screws back in.

The restrictor plate looks like this:


The Kawasaki manual calls this piece the spark arrester. I think they do that to try and scare you. The parts diagram on the Kawasaki website calls it the "Baffle-pipe, muffler". I asked the dealer if the spark arrester still stopped sparks with the cover off and he said it did (shrug).

This mod will make the bike a lot louder, so your neighbors might not like it if you run the bike at home a lot after making this mod. It also leaves a gaping hole in the back of the can, so be careful when hosing down your bike. Don't get any water in there if you can avoid it.

4. Replace the crankcase filter.

This mod isn't as popular, but is supposed to help significantly as well. The deal is that the stock crankcase breather hose has a brass couple in it that has a really small hole in it that restricts airflow. A bigger hose without a coupler is supposed to help. You run the hose up into the airbox and stick the little filter on the end.

You can get all of the crankcase breather stuff from your local auto parts store.

User Feedback

Recommended Comments

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Add a comment...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Similar Content

    • By Tim Ogrady
      I have seen different shocks fit to the kmx and am wondering will a klx 250 one do, or is there modifications that have to be done ????
    • By My_minibike_is-900-horspwr
      Looking for a 125 2 stroke to ride on my 2 acre property and trails. (I'm aware this isn't the ideal bike for my use case but it's all I can afford. Trail bikes are WAY more $$ in my area. Also my property is actually set up quite nicely for this purpose regardless of how small that sounds for rideing)
      Basically I won't have enough space for top end power, so I need low end. Here are my specific questions:
      1) which is most reliable in your opinion and why?
      2) which has the most low end power/acceleration?
      3) if different, which can safely go longest without a top end rebuild?
      4) which handles slow speeds the best?
      5) for those who've ridden multiple, which do you recommend for my use case?
      Keep in mind that these questions are relating only to mid 90s through mid 2000s 125s. Also ktms are usually about a 3rd more expensive here, but key me know their benifits none the less.
      I would just look for a 4 stroke trail bike, but again, in my area, they're too expensive for me. Basically the only full size, fairly modern dirt bike I can afford is a 125 2t, so please don't just tell me to buy a crf250; I can't. Thanks!
    • By Chris.GVS
      We obtained a pre-production 2018 Husqvarna TE 250i to flog, and we wasted no time in logging 80 grueling miles on the new Husky across three of the most technically challenging trails in Southern California.
      Here are the 14 essential facts you need to know about the new fuel-injected Husky TE 250i two-stroke
      Type: Single-cylinder, power-valve 2-stroke Displacement: 249cc Bore x stroke: 66.4 x 72mm Fueling: EFI w/ 39mm Dell’Orto throttle body Induction: Reed valve Ignition: Synerject EMS Silencer: Aluminum Cooling: Liquid Starting: Electric and kick Lubrication: Electronically regulated oil injection Transmission: 6-speed Clutch: DDS wet multi-disc clutch w/ Magura hydraulics Final drive: X-chain CHASSIS
      Frame: Central double-cradle-type chromoly steel Subframe: Carbon fiber reinforced polyamide Handlebar: Pro Taper; Aluminum Ø 28/22 mm Front suspension; travel: Fully adjustable inverted WP Xplor 48mm fork; 11.8 inches Rear suspension: Linkage-assisted fully adjustable WP DDC shock; 13.0 inches Front rim: 1.60 x 21”; DID Dirt Star Rear rim: 2.15 x 18”; DID Dirt Star Front tire: 90/90-21; Dunlop Geomax AT81F Rear tire: 14079-18; Dunlop Geomax AT81 Front brake: 260mm disc w/ Magura hydraulics Rear brake: 220mm disc w/ Magura hydraulics DIMENSIONS and CAPACITIES
      Wheelbase: 58.9 inches Rake: 26.5° Triple clamp offset: 22mm Seat height: 37.8 inches Ground clearance: 14.6 inches Tank capacity: 2.4 gallons (approx.) Wet weight: 247 pounds (approx.)
    • By Chris.GVS
      This thing flat hauls. It stood it up in all six gears with a sharp Metzler tire on the back and a quick whack of the throttle. It would claw it's way skyward with sheer torque, then hang it there until you get scared on sheer juice.
      Now has a Kehin FCR41 carb feedin the retro Pro Circuit- pushed reed cage (Mossensomething?) it's the absolute fastest thing in the single track of BC
      1985 Husqvarna XC500 Specifications

      Engine Type 2-stroke
      Displacement 500 cc
      Bore x Stroke 86 mm x 84 mm
      Engine Cooling Liquid
      Spark Plug Bosch W4c
      Carburetor 40mm Mikuni
      Transmission 6 - speed
      Steering Rake (Castor) 27 degrees
      Steering Trail 4.72 in
      Wheelbase 59.5 in
      Ground Clearance 15.4 in
      Seat Height 38.4 in
      Weight, dry 235 pounds
      Fuel Tank Capacity 3.2 gallons
      Forks 40mm Husqvarna
      Fork Travel 11.8 in
      Shock(s) Ohlins, Single
      Shock Travel 13.8 in
      Wheels and Tires
      Front Wheel 21 in
      Rear Wheel 18 in
      Brakes disk/drum
    • By Antigravity Batteries
      Just want to share a big congratulations to Eli Tomac on the 2020 450SX Monster Energy Supercross championship! This marks the 11th 450SX championship for Kawasaki in Monster Energy Supercross and Antigravity Batteries are proud to power and be a part of this huge win!

  • Create New...