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KX100 idling problems

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Ever sense I got my bike, a 06 kx100 it wouldn't idle for beans. Unless it was one the choke, then it would idle, very high. We took off the carb and blew it out but still no help. Im not sure if the fact that it has V-force reeds or a pro circuit full system has to do with it. Hopefully not. But anyway, later me and my dad are gonna check the plug and airfilter but if those dont help what else should we look for? Thanks in advance :thumbsup:

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remove you pilot jet and slide a wire from a wire brush through it, to make sure that it is not clogged, that controls the idle.

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Its not idling right already? Blowing the jets with compressed air should be fine. I am guessing the jetting or the reeds are the culprit. good luck. hope you fix it.

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it never idled when i got it

keep the suggestions coming guys

did you ask the previous owner if there was anything wrong with it? Did you start it up when you bought it and notice the idle problem?

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have you tried adjusting the idle screw?

on my bikre its the black plastic one with the spring,wind it into raise the idle.

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thats weird.... id still take a closer look at the pilot jet (and screw), and check the float bowl adjustment.

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First, check the reeds. Worn, cracked or chipped reeds will make a mess of the jetting, and you'll never get it to idle or run clean at small throttle openings.

Once you know the reeds are in good shape, or have replaced them if neccessary, make sure the pilot jet isn't clogged, and the pilot air passageway in the carb body.

Set the idle screw in, and turn the air screw out to 1.5 turns from fully closed.

With the engine fully warmed up, hold the engine at a slightly fast idle, and start opening the air screw until you find the point where the idle speed peaks. If this is more than 2 turns out, you need a leaner (smaller number) pilot jet. The idle should peak witgh the air screw around 1.5 turns from fully closed with a correctly-sized pilot jet.

If the air screw has no effect on the idle, then the pilot jet is way off, and you'll probably need to go at least 2 sizes smaller before you get in the ballpark.

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Print this out.

Jetting 101:

A correctly jetted carb makes a tremendous difference in the torque, midrange pull, top-end pull, and over-rev of your engine. If you have never jetted your bike correctly, you will almost certainly gain some performance at some point in the bike's powerband.

A cleanly jetted pilot circuit can be the difference between having to clutch the bike out of a turn or not. Hard starting when hot or cold, poor response when opening the throttle, reluctance to idle, all of these are symptoms of an improperly sized pilot jet or incorrectly adjusted air screw.

The needle can make all the difference in the world for the power of the machine in most situations, as it controls the throttle range that most riders spend most of their time using.

A correctly sized main jet could mean the difference between being able to rev out high enough to not have to shift one more time at the end of the straight, or the power falling flat on top and requiring you to make that extra shift.

Are you fouling plugs? Many people will tell you all sorts of band-aid fixes, from running less oil, to running a hotter plug. Both are incorrect fixes for plug fouling. It's all in the jetting. An engine that is jetted too rich will have combustion temperatures that are too low to burn the fuel and oil effectively, leading to deposits and wet fouling of the plugs.

Do you have spooge? There are the rare instances where a mechanical issue, such as a leaking wet-side crank seal, can cause spooge. But, by and large, this isn’t the case. In most instances, spooge is caused by rich jetting. It has nothing to do with how much oil you mix in the gas, or how hard you ride. An engine that is jetted too rich will have combustion temperatures that are too low to burn the fuel and oil effectively, resulting in deposits, plug fouling, and spooge. Spooge is nothing more than unburned fuel and oil entering the exhaust.

The only way to know what jetting changes you will need is by trial-and-error. No one can give you jetting specs, because every bike is different, every rider has a different style, and jetting is totally weather dependent. Unless the person telling you what jets to use is riding an identical bike, on the exact same track, at the same time, his recommendations are meaningless. Someone with a good understanding of jetting can get you in the ball park, but you need to do the testing to determine the correct jetting yourself if you want it right.

Jetting is fairly simple, and is a useful skill to learn if you ride a two-stroke and want it to perform at it's best.

It's very important that you start with the pilot circuit, because the pilot circuit affects the entire throttle range. When you are at full throttle, the main jet is the primary fuel metering device, but the pilot is still delivering fuel as well, adding to the total amount of fuel that your engine is receiving.

Before you start to re-jet your bike, you need a clean air filter, a fresh plug (actually you need several plugs to do plug-chop tests for the main jet), and fresh fuel.

One important detail: Make sure the engine is in good mechanical condition. If your engine has a worn top-end, fix it first. Trying to jet a worn out engine is a waste of time. The same goes for reeds that don't seal properly, and a silencer that needs re-packing. Worn reeds will mimic rich jetting, and worn rings will mimic lean jetting.

Before you start the jet testing, Install a fresh plug. Set the float level to the proper specs, an incorrect float height will affect your jetting all across the throttle range.

All jet testing must be done with the engine at full operating temperature.

As already stated, start with the pilot circuit. Turn the air screw all the way in, then turn it out 1.5 turns to start. Start the engine, and turn the idle screw in until you get a slightly fast idle, or hold the throttle just barely cracked, to keep the engine idling. Turn the air screw slowly in, and then out, until you find the point where the idle is fastest. Stop there. Do not open the screw any farther, or your throttle response will be flat and mushy, and the bike may even bog. This is only the starting point, we will still have to tune the air screw for the best response.

Now is the time to determine if you have the correct pilot installed in your carb. The air screw position determines this for you, making it very simple. If your air screw is less than 1 turn from closed, you need a larger pilot jet. If it is more than 2.5 turns from closed, you need a smaller pilot jet. If your engine doesn’t respond to air screw changes, then you either have a dirty carb, or the pilot jet is way too rich. When the pilot jet is way too rich, you are forced to use the idle screw to open the slide so far in order to keep the engine running that the pilot circuit is partially bypassed, and the engine is actually starting to draw fuel through the needle jet.

Once you have determined (and installed it if it's necessary to change it) the correct pilot jet size, and tuned the air screw for the fastest idle, it's time to tune the air screw for the best throttle response. Again, make sure the bike is at full operating temperature. Set the idle back down (the bike should still idle, despite what you read in the Moto Tabloids), and ride the bike, using closed-to-1/4 throttle transitions. Turn the air screw slightly in either direction until you find the point that gives you the best response when cracking the throttle open. Most bikes are sensitive to changes as small as 1/8 of a turn.

The air screw is not a set-it-and-leave-it adjustment. You have to constantly re-adjust the air screw to compensate for changing outdoor temps and humidity. An air screw setting that is perfect in the cool morning air will likely be too rich in the heat of the mid-day.

Now, it's time to work on the needle. Mark the throttle grip at 1/4 and 3/4 openings. Ride the bike between these two marks. If the bike bogs for a second before responding to throttle, lower the clip (raising the needle) a notch at a time until the engine picks up smoothly. If the bike sputters or sounds rough when giving it throttle, raise the clip (lowering the needle) until it runs cleanly. There isn't really any way to test the needle other than by feel, but it's usually quite obvious when it's right or wrong. A too-rich needle can often be felt simply when revving the bike on the stand. The bike will sound rough and raspy when blipping the throttle on the stand. A correctly jetted bike should rev cleanly and crisply.

Last is the main jet. The main jet affects from 1/2 to full throttle. The easiest way to test it is to do a throttle-chop test. With the bike fully warmed up, find a long straight, and install a fresh plug. Start the engine, and do a full-throttle run down the straight, through all gears. As soon as the bike tops out, pull the clutch in, and kill the engine, coasting to a stop. Remove the plug, and look deep down inside the threads, at the base of the insulator. If it is white or gray, the main is too lean. If it is dark brown or black, the main is too rich. The correct color is a medium-dark mocha brown or tan.

Please note that, when reading plugs, the tip of the insulator, threads, etc. are meaningless for jetting purposes. They can tell you a lot of things, but jetting isn’t one of them. Only the mixture ring at the very base of the insulator, inside the threads, can tell you anything about the jetting.

These links should help you to understand reading plugs:

http://www.tsrsoftware.com/images/sparkplug.gif

http://www.tsrsoftware.com/read-plugs_files/sparkplug b-w .gif

The slide is also a tuning variable for jetting, affecting the throttle range from 1/8 throttle to approximately 1/3 throttle. If you can’t clean up the small-throttle jetting on your bike no matter how lean you go with the pilot or the needle, the slide is the next step. But few bikes need leaner slides.

Keep in mind, even though this article is intended primarily for two-strokes, four-strokes also need proper jetting to perform right, although they are not quite as fussy as their oil-burning cousins. The only real difference in the two is with the pilot circuit.

Two-strokes have an air screw that you screw in to make the jetting richer, and screw out to make the jetting leaner. Four-strokes, on the other hand, have a fuel adjustment screw that you screw in to make the jetting leaner, and out to make it richer. Their purpose is the same, they just do it in different ways.

Four-stroke carbs also use an accelerator pump. By nature, four-stroke engines have a much weaker vacuum signal to the carb at small throttle openings, so they tend to hesitate when whacking the throttle open, because it takes a small amount of time for the weaker vacuum signal to begin drawing fuel up through the jets. To compensate for this, the accelerator pump squirts a small stream of fuel into the carb throat. The accelerator pump must be correctly adjusted for flow volume and timed for flow duration. Too much fuel squirt, and the bike can flood, especially on a tight track where frequent off-on throttle transitions are necessary. Too little, and the bike bogs coming out of turns and when landing from jumps. Every four-stroke model is different, so refer to your manual for correct adjustment of the accelerator pump.

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Thanks Chokey, gas for you!

Edit: "you must spread around more reputation before giving to Chokey again" darn

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quick question:

what would you guys recommend for jet sizes for my 100?

i live at about 500 ft and normally around 60-70 degrees now

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Thanks Chokey, gas for you!

Edit: "you must spread around more reputation before giving to Chokey again" darn

I had to give him gas for that awesome post.

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quick question:

what would you guys recommend for jet sizes for my 100?

i live at about 500 ft and normally around 60-70 degrees now

anyone have any suggestions :thumbsup:

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I don't know the stock jet sizes, but it doesn't really matter. If you verify that everything is in good mechanical condition, then regardless of what size pilot jet is in the carb, it's obviously too rich. Pull out the existing pilot jet, take it to the dealer, and get at least two smaller (leaner) sizes, maybe even three. Start with the next-leaner jet and tune from there.

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