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KDX Gas Mixture

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I run 32:1 on my 97 KDX and iit has a pipe and silencer from FMF and the bike is rejetted for the pipe and such but it still spits a good amount of oil from the exhaust. Should I lean out my gas mixture, and to what ratio?

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my bike was doing the same, i droped a pilot and main jet. Try doing the same. If it only seems to be putting out alot of smoke when the throttle is closed to like 1/3 open turn your air screw out a little bit and see how it works. It will take a few minutes of riding to see the results.

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I run 50:1 synthetic-(Amsoil Dominator). stock jetting, and very little smoke or oil spooge. Since I got it new in '02.

how many top ends have you gone through?

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how many top ends have you gone through?

I've raced almost 22 years mixing at 42:1, and 50:1, and have NEVER lost a top end due to too lean an oil/fuel ratio.

90% of engine siezures are from an overly dirty AIR FILTER sucking dirt. The other 10% are from ignorant idiots who forgot to mix their oil with the gas.

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None. And, I ride rather hard. All single track or 2 track, with my 3 boys, who are on kx 85, kx 100, and kx250f. So, if I am not on it, I have to eat their dust. That doesn't happen. yet.....

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In the past I'd always ran Golden Spectro at 52:1 in my smokers with no problems.

Since I just got the little KDX-200 for my first 5 gals I'll run at 40:1 then it'll be 52:1 after that.

.

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Agree w/the 40 and 50:1 mixes. 32 to 1 has too much oil in it (but actually leaner...less gas w/same air equals leaner mixture).

I've had my KDX 200 since 2003 (three years) w/a lot of So Cal Desert riding, including all summer, no overheats, and compression hasn't budged since I've owned the bike.

I also leaned the pilot jet, and needle a "step" to help clean things up.

To make sure we're comparing apples/apples oranges/oranges, what elevation/temp do you usually ride at? Cold sea level conditions w/a over-lean carb could spell some bad news for your top end if not carefull.

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I run 32:1 on my 97 KDX and iit has a pipe and silencer from FMF and the bike is rejetted for the pipe and such but it still spits a good amount of oil from the exhaust. Should I lean out my gas mixture, and to what ratio?

This is something that needs more research on your part. What is your altitude, temp,humidity,most important is what size main and pilot jet are you running? What needle and clip position on said needle? How far out or in is your air screw? Is the pipe a rev or woods? The part number should be on the mount tab of the pipe under the Fuel tank if the last to numbers are 57 its a woods pipe 56 is a rev. Read

You can change the mix ratio but that is not a good way to control spooge. more oil means less gas leaner running condition 32:1 is as lean gas wise as you should go. less oil say 50:1 you richen up the running condition. two ways to foul plugs to much gas or to much gas and oil.

The best thing to do is find out what your base line is now (find the answers to the above questions) and buy 3 sizes of jets and needles, and a hand full of spark plugs, start playing until it looks and feels good. Stick with what ever mix ratio you decide to run, until all the fine tunning is done.

I change my ratio from summer 40:1 to 50:1 winter, as well as change to leaner jetting in the summer. It is hard to run it lean in 40% humidity and 90-100 degree temps.

This was copied from kdxrider.net/forums/viewtopic.php?t=1156

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. 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.

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.

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. The reason is simple. 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 rejet 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.

Warm the bike completely, and shut it off.

As already stated, start with the pilot circuit. Turn the airscrew 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 idleing. Turn the airscrew 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 airscrew for the best response.

Now is the time to determine if you have the correct pilot installed in your carb. The airscrew position determines this for you, making it very

simple. If your airscrew 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.

Once you have determined (and installed it if it's necessary to change it) the correct pilot jet size, and tuned the airscrew for the fastest idle, it's

time to tune the airscrew 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 airscrew 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 airscrew is not a set-it-and-leave-it adjustment. You have to

constantly re-adjust the airscrew to compensate for changing outdoor temps and humidity. An airscrew 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.

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.

Once you have a little bit of experience with jetting changes, and you

start to learn the difference in feel between "rich" and "lean", you'll begin to learn, just from the sound of the exhaust and the feel of the power, not

only if the bike is running rich or lean, but even which one of the carb circuits is the culprit.

The slide is also a tuning variable for jetting, but slides are very expensive, and few bikes need different slides, so we won't go into that

here.

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The pipe is a kx250 fatty pipe, it's kind of ghetto mounted on there but it makes the bike run really good. The dealer and my brother took care of the jetting so I really don't know what it's at. I'm not good at jetting

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if a 16 year old can do it, so can you. Acutally my dealer did it for me then explained jetting 101. Now i realize fairly what is going on. I will soon be switching from 32:1 to 40:1 which means i have to drop my pilot from a 42 to a 40 and my main from a 155 to a 152.

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Hey, I give you lot's of credit. You can spell, which is more than a lot of the kids that post here. That jetting tip is 100% right on.

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if a 16 year old can do it, so can you. Acutally my dealer did it for me then explained jetting 101. Now i realize fairly what is going on. I will soon be switching from 32:1 to 40:1 which means i have to drop my pilot from a 42 to a 40 and my main from a 155 to a 152.

When you try to dial in your jetting, remember this : make ONE change at a time! This way you incramentally know if you are moving in the right direction or not. FIRST lean out your fuel/oil mixture, then ride your bike for a weekend paying close attention to it's behavior, and plug color. You want your plug's insulator to be a deep chocolate color. If you plug still seems wet and black, try just moving the needle 1 clip leaner (most of the time you don't even need to remove the carb for this adjustment).

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The pipe is a kx250 fatty pipe, it's kind of ghetto mounted on there but it makes the bike run really good. The dealer and my brother took care of the jetting so I really don't know what it's at. I'm not good at jetting

Wow, I don't know about that. Two-stroke expansion chambers are extremely fine-tuned devices. It probably isn't the best idea to stick a pipe from a completely different engine on another completely different engine.

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When you try to dial in your jetting, remember this : make ONE change at a time! This way you incramentally know if you are moving in the right direction or not. FIRST lean out your fuel/oil mixture, then ride your bike for a weekend paying close attention to it's behavior, and plug color. You want your plug's insulator to be a deep chocolate color. If you plug still seems wet and black, try just moving the needle 1 clip leaner (most of the time you don't even need to remove the carb for this adjustment).

i know ive worked on many two strokes and jetting was very tough for me in the begining, now it is very easy for me although i do get confused sometimes.

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Wow, I don't know about that. Two-stroke expansion chambers are extremely fine-tuned devices. It probably isn't the best idea to stick a pipe from a completely different engine on another completely different engine.

It's an FMF pipe not a stock pipe and it works really good :thumbsup:

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You guys keep talking about plugs though, and I have never fouled a plug on this bike and it stays new for a fairly long time, there's just excess coming out of my silencer that I'd like to attempt to get rid of.

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