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kdx rejetting

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I have a 2002 kdx200 and it's running way to rich. It will spit oil out onto the back fender and run down the pipe when i ride. I have a fmf gnarly pipe, and fmf turbine core 2 silencer. I am running it at 50/1 mixture but it still runs rich. Which rejetting kit should i get and where should i get it. thanks

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I wouldn't say a rejet kit will fix that. Should check the needle and seat and float out. Have seen it on more than a few KDX's where it would stick and cause those symptoms. I have stock jetting still on my 04 with the FMF pipe and silencer. Runs crisp and clean here at 2500 ft. I mix it 40-1.

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I agree, look at the needle/float. I still have stock jetting in my '02 here in Northern Mi, and stock pipe. I also run 50:1, very little smoke.

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I have a 2002 kdx200 and it's running way to rich. It will spit oil out onto the back fender and run down the pipe when i ride. I have a fmf gnarly pipe, and fmf turbine core 2 silencer. I am running it at 50/1 mixture but it still runs rich. Which rejetting kit should i get and where should i get it. thanks

How long have you been running 50:1? If you, or the previous owner have been running a very rich mixture (32:1) I may take a month to get all the oil "spooge" burned out of the engine and exhaust.

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50:1 40:1 32:1 etc. Nothing compares to good jetting. Work with your needle and float. Too many people try to "jet" their bikes by adjusting the ratios. Put in the effort and go for broke. Try Fredette racing and see what they recommend. I got some jetting help from them and it worked wonders. Dont overlook the pilot jet!

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I might consider rejetting after my experience tonight. My KDX200 had been running pretty good since i got it 3 weeks ago. It would bog down slightly when i firsted started riding but after about 100 yards it was fine. Tonight i jumped on it to go and it just would not go, bogged down, sounded and ran like garbage. I checked the sparkplug and it was a mess so i replaced it. I'm going to run a little leaner mixer, 36/1 or 40/1 to see if that makes a difference. If i have to i'll rejet, although it does run strong once it gets warmed up. I've never rejetted a bike before so i'm a little nervous to do it.

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They come jetted too rich from the factory. Try starting with a 155 main, raise clip on needle to 2nd position, and 40 pilot. This is just a starting point. You may still need to jet leaner in one or more circuits. Adding less oil in the mix will make the air/fuel ratio richer increasing the oil problem.

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50:1 40:1 32:1 etc. Nothing compares to good jetting. Work with your needle and float. Too many people try to "jet" their bikes by adjusting the ratios. Put in the effort and go for broke. Try Fredette racing and see what they recommend. I got some jetting help from them and it worked wonders. Dont overlook the pilot jet!

There are TWO types of fouling. Rich jetting, and overly rich oil/fuel mixtures. KDX's come jetted slightly rich from the factory, unlike the KX's which come jetted very rich.

Like I have commented dozens of times, people feel they have to mix thier ratios at 32:1 because thats what the factories recommend. The factories recommend this with the assumption the rider is an expert, and will be holding his bike WOT for a 45 min. moto. The factories don't want an engine to blow up a week after the customer takes it home when new. 99% of the sport or weekend fun racer riders can, and should be mixing ratios at 42:1, even 50:1 for woods riders, or new riders. Most people also don't realize you loose some power by richer oil ratios. The more oil in the gas, the slower the combustion. Jetting leaner can be disasterous if you don't know what your doing. My advice is premix at 42:1, and I about guarantee you won't need to rejet (at least bone stock bikes). Remember one fact...... It's easier and cheaper to replace a $6 plug, than it is the replace a $140+ top end.

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I might consider rejetting after my experience tonight. My KDX200 had been running pretty good since i got it 3 weeks ago. It would bog down slightly when i firsted started riding but after about 100 yards it was fine. Tonight i jumped on it to go and it just would not go, bogged down, sounded and ran like garbage. I checked the sparkplug and it was a mess so i replaced it. I'm going to run a little leaner mixer, 36/1 or 40/1 to see if that makes a difference. If i have to i'll rejet, although it does run strong once it gets warmed up. I've never rejetted a bike before so i'm a little nervous to do it.

I'd bet it was hotter outside / more humid the last time you rode. Bike could probably have used a bit leaner air screw setting.

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This is taken from www.justkdx.dirtrider.net

"Before we get into the different parts of the carburetor and how they effect gasoline delivery I want to stop for a second and define the terms RICHER and LEANER. I know these terms can cause some trouble for those who are new to the sport or new to carburetor tuning and they are often used incorrectly. The terms RICHER and LEANER refer to the amount of GASOLINE being delivered to the engine and not the amount of oil. If you’ve done a plug reading at wide open throttle and the plug indicates you are running rich ( dark brown to black ) this is an indication that too much gas is being delivered to the engine and not too much oil. I know there are people that will say "You’re running too rich, try to change your premix ration from 42 parts gas: 1 part oil ( 42:1 ) to 50 parts gas : 1 part oil, that should lean things out a little ". This is in fact increasing the amount of gasoline ( 8 more parts of gas for each part of oil ) and causing the engine to run RICHER rather than leaner. If you remember richer and leaner are referring to the amount of gasoline being delivered this will all make much more sense."

Putting less oil in the mix will actually make the jetting richer, increasing your oil spewing problem. I've owned an "H" model kdx200 for years and they are fall on your face rich from the factory. If you have no air leaks you can safely run a 155 main. I run a 152 in mine and it's still a little rich. Whatever premix ratio you decide to use, you should stick to that ratio and jet for it by doing plug chops to make sure you're not too lean. Trying to get rid of the spooge by adjusting oil amount will never work.

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I helped many friends get their jetting dialed in. A lot of the times I find I can get a bike to run excellent simply by leaning out the needle clip position, which dictates 1/4 to 3/4 throttle engine behavior. This is where most of us spend all of our time. The biggest complaint I hear is "my bike fouls plugs in the woods" or it runs bad idle to 1/2 throttle. This is when I focus also on the pilot jet.

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I helped many friends get their jetting dialed in. A lot of the times I find I can get a bike to run excellent simply by leaning out the needle clip position, which dictates 1/4 to 3/4 throttle engine behavior. This is where most of us spend all of our time. The biggest complaint I hear is "my bike fouls plugs in the woods" or it runs bad idle to 1/2 throttle. This is when I focus also on the pilot jet.

That's true and I've never heard of anyone frying a topend by accidently going too lean on the needle or pilot. :thumbsup:

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can someone please tell me why my kdx220 runs richer than stock with a uni filter and an fmf gnarly desert pipe. I was expecting the bike to run leaner but this was the first aftermarket pipe i've put on a bike. I'm thinking of moving the clip position up(im not sure what its et on now tho) and maybe a size leaner pilot jet, ill keep my stock main for now because it runs well at WOT just not down low. Can someone tell me what the stock pilot jet size is on a 220's carb thanks for any advice

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Most people also don't realize you loose some power by richer oil ratios. The more oil in the gas, the slower the combustion. Jetting leaner can be disasterous if you don't know what your doing. My advice is premix at 42:1, and I about guarantee you won't need to rejet (at least bone stock bikes). Remember one fact...... It's easier and cheaper to replace a $6 plug, than it is the replace a $140+ top end.

You need to back up a little throwing out these contradictions and blanket statements. This won't get Redrider anywhere.

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There are TWO types of fouling. Rich jetting, and overly rich oil/fuel mixtures. KDX's come jetted slightly rich from the factory, unlike the KX's which come jetted very rich.

Like I have commented dozens of times, people feel they have to mix thier ratios at 32:1 because thats what the factories recommend. The factories recommend this with the assumption the rider is an expert, and will be holding his bike WOT for a 45 min. moto. The factories don't want an engine to blow up a week after the customer takes it home when new. 99% of the sport or weekend fun racer riders can, and should be mixing ratios at 42:1, even 50:1 for woods riders, or new riders. Most people also don't realize you loose some power by richer oil ratios. The more oil in the gas, the slower the combustion. Jetting leaner can be disasterous if you don't know what your doing. My advice is premix at 42:1, and I about guarantee you won't need to rejet (at least bone stock bikes). Remember one fact...... It's easier and cheaper to replace a $6 plug, than it is the replace a $140+ top end.

Sorry to be blunt, but most of that is a load of crap.
You lose power by richer oil ratios
? On the contrary, dyno testing proves that two-strokes make more power with more oil in the mix. They make their best power at around 18:1.
The more oil in the gas, the slower the combustion
? Where did you pull that one from? Changing your mix ratio is not going to change the flame speed of the fuel. The oil amount (and even the brand) will effect the burn characteristics, but it will not alter the flame speed of the gasoline one bit. The oil is consumed by the burning fuel, but it does not contribute to the power-producing combustion process of the gasoline.
and I about guarantee you won't need to rejet (at least bone stock bikes).
All bikes need to be jetted correctly according to conditions, even those that come jetted pretty close stock (KDXs don't). Japanese motocross bikes come jetted for an imaginary ideal of 70 degrees, 50% humidity, and sea level. And even with that as the goal, the testing and development people often get it slightly wrong, and sometimes (like on the KDX) they are way off.

Jetting is totally dependent on atmospheric conditions. Changes in altitude, temperature, and humidity all change the amount of oxygen available to the engine, requiring changes to the jetting to maintain correct combustion temperatures.

Now to the spooge. Assuming your engine is mechanically sound (no leaking crank seals, reeds in good condition, etc.), spooge is caused by rich jetting. Nothing else. If your bike spooges, it's jetted too rich to achieve high enough combustion temepratures to consume the oil.

KDXs are well known to be jetted ridiculously rich from the factory. If you are running stock jetting in a KDX, even if you don't feel that you have a spooge problem, you are losing out on a lot of hidden performance that you didn't even know your bike had. A correctly jetted and uncorked KDX is night-and-day better than a stock one. If you live from sea level to 1500 feet, you'll want a 152-155 main, a 45-48 pilot, and the needle in the second or top clip position to make the bike run right. An 1173 needle is even better. If you live at higher elevations you'll need to jet even leaner.

There is a prevailing myth that less oil is better, and that mix ratios are one-size-fits-all. Nothing could be farther from the truth.

The best way to determine if you are running enough oil is to check the level of the residual oil in the crankcase. If the ratio you run leaves enough residual oil in the crankcase to cover about 1/8" of the bottom of the crank wheels, then you are fine. If you don't have that much residual oil in your crankcase when you pull the top-end off, you aren't running enough oil for your riding style and conditions.

If you are running enough oil in your mix to properly coat and lubricate everything, then when you shut the engine off and let it sit, enough oil will drain down into the bottom of the crankcase to form a small puddle. That's your indicator of whether or not you are running the correct ratio for oyur conditions.

With that said, to have that amount of residual oil in the crankcase at 50:1 (a ratio made popular by magazines and oil bottles), you can't be riding very hard, or your bike is jetted richer than necessary simply to deliver enough oil. I arrived at 26:1 for my bike with my riding style because that is the amount that gives me the proper amount of residual build-up. Small-bore engines require greater oil concentrations than larger engines to achieve the proper amount of residual build-up, because they rev higher and have higher intake velocities. Along the same lines, someone that pushes the engine harder, and keeps the revs higher, also needs to use higher oil concentrations to achieve the proper residual build-up.

To understand why the residual oil is so important, you have to understand what happens to the oil in your fuel when it goes into the engine. While the oil is still suspended in the liquid gasoline, it can not lubricate anything. It has about as much lubricity at that point as straight gasoline. When the gasoline enters the engine, it evaporates, dropping the oil out of suspension. Now that the oil is free, it can lubricate the engine, but it must get to the parts to lubricate them. The way it gets to the bearings and onto the cylinder is by being thrown around by the spinning crankshaft, and being distributed through the engine by the air currents moving through the crankcase.

The oil eventually makes it into the combustion chamber, where it is either burned, or passes out the exhaust. If the combustion chamber temps are too low, such as in an engine that is jetted too rich, the oil doesn't burn completely. Instead, some of it hardens into deposits in the combustion chamber, on the piston, and on the power valve assembly. The rest becomes the dreaded "spooge". The key to all of this working in harmony is to jet the bike lean enough to achieve a high enough combustion chamber temperature to burn the oil, but also still be able to supply enough oil to protect the engine. If you use enough oil, you can jet the bike at it's optimum without starving the engine of oil, and have excellent power, with minimal deposits and spooge. At 50:1, you simply can't jet very lean without risking a seized engine due to oil starvation.

One small point. No one ever broke an engine by using too much oil.

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