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While riding my bike the other day the thing just died. It was like the gas just shut off. I gave it a quick once over and let it sit for a few minutes. I was able to kick it over and run for about 10-15 seconds and was unable to start it again. It seems like its not getting fuel or spark.

I did a couple things before this ride. I changed the oil in the gear box with 80w gear oil (which is the same as SAE30). I also used a different type of pre-mix oil. The bike has always used Lucas 2cycle. I couldnt find it, so i went with a Castor 927 mixed @ 24:1.The fuel mixture is the same as its always been with Lucas.

I got the thing home and drained the gas, and used Lucas oil mixture. I also cleaned the carb/drained the gear oil/cleaned the spark plug. Still wont kick over.

I noticed at this point that the clutch wouldnt engage. I can shift the gears, but the bike wont roll when the clutch is pulled in. I pulled the plate off of the flywheel housing to inspect the cable and noticed what seemed to be a oil/fuel mixture in this compartment. I read in different forums that the KTM 250Sx has oil around the stator, so i think that is ok.

Bottom line. I need help.

Any suggestions would be greatly appreciated. Thanks

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what year ktm? there shouldnt be oil around the stator on a 2 stroke.

1st thing i would do is put a fresh plug in, not a cleaned up one. the bike needs air, fuel, spark and compression. eliminate those one by one....

Edited by Dirt Addict

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first sanded the tips on the spark plug, then ripped into the bike pretty good with no luck.....Went and bought a new spark plug put it in and kicked it over on the first kick. Ya, i am pretty lame! one wasted weekend down!

using a leaner 40:1 but the low end seems to bogg until i give it some gas for a little bit.

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Care to explain this?

What is there to explain? If your bike is jetted properly, you can run whatever ratio you want. Pick a ratio and jet for it.

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first sanded the tips on the spark plug, then ripped into the bike pretty good with no luck.....Went and bought a new spark plug put it in and kicked it over on the first kick. Ya, i am pretty lame! one wasted weekend down!

using a leaner 40:1 but the low end seems to bogg until i give it some gas for a little bit.

It is hard to follow the ratio when you guys talk richer with more oil. You actually make the fuel to air ratio leaner when you add more oil. The fuel viscosity is thicker therefore it passes thru the jets at a slower velocity. When you switched to 40:1 you made the bike run richer because less oil makes the fuel a thinner viscosity. If I remember right you get more horse power and longer engine life out of a 2 stroke when you use more oil. You need to jet accordingly and find the jetting needed to keep from fouling plugs. I personally liked running my bikes at 32:1 and jetted to that ratio and stuck with it. I think your issue began with running the Castor 927 with Lucas premix still in the bike. That Castor does not mix easy you need to dilute it in your ratio rite back and forth or it sits like a big lump in the gas can.

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way.

What is there to explain? If your bike is jetted properly, you can run whatever ratio you want. Pick a ratio and jet for it.

I dont think it works that way to a point. you cant just keep adding oil and making it run leaner and leaner to burn the extra oil of the plug can you? I am trying to learn here.

Edited by Stillhavetimeleft

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I have a 07 250sx with a 300 kit. It started fouling plugs. I found a bare wire at the stator. I made a new harness and eveything is good now. Of course I found the wire after trouble shooting everything else. Oh well, new crank seals never hurt anything.

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I dont think it works that way to a point. you cant just keep adding oil and making it run leaner and leaner to burn the extra oil of the plug can you? I am trying to learn here.

Of course you can't just keep adding oil. You have to also adjust your jetting. You can run however much oil you want, but you need to adjust your jetting to accommodate your mix ratio. Hence, having your bike jetted properly. There is no one "proper" jetting. Pick a ratio and jet for it.

Edited by KcDavis

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Hmmm, I would have to disagree that there is no one proper jetting. First off its important to note, as KX290 pointed out, that 40:1 is richer (less oil, more fuel) than 20:1 (more oil, less fuel)...this is a common misnomer with 2 strokes. Rich and lean refer to fuel and air, not oil...how else could a 4t can be lean or rich?..same basic concept. Incorrect jetting, too rich or too lean will decrease performance..especially in a 2t, which seem more sensitive to jetting changes. In the case of too lean jetting, you can sieze a piston and spin your bearings. I would say thats a problem. KTM suggests 60:1 with premium oil...in the manual. I run 46:1 with Motul Synthetic (800)...but everyone has an opinion on this matter.

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Of course you can't just keep adding oil. You have to also adjust your jetting. You can run however much oil you want, but you need to adjust your jetting to accommodate your mix ratio. Hence, having your bike jetted properly. There is no one "proper" jetting. Pick a ratio and jet for it.

So if I mix it to 20:1 that means there is half fuel going in than 40:1 so I would have to richen the jetting a lot to get that fuel back in there.... but sooo much oil would be getting in there... 4 times as much I think. Can it still actually run clean with 4 times the oil?

Edited by Stillhavetimeleft

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Generally, I agree that riders should pick a ratio and jet accordingly, but this rule shouldnt be taken to the extreme...ie 10:1 or 100:1 I think its good advise and holds true up to a point, which IMO, is common sense. Who really runs 20:1 with modern synthetic oil? I know a guy thats running 100:1 with Redline...I suspect he will be due a rebuild soon. I would say the rule holds from about 30:1 to 60:1. Outside of that range, all bets are off.

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You can jet around 2 much oil all you want but it's just not good for an engine.

If the top of your piston is all covered in black carbon, then you have too much oil.

There should be a spot about the size of half a thumnail on each side of ther piston crown where the transfer ports enter where the piston is 'clean'. If you run too much 2 stroke oil, even jetted correctly, your engine will run dramatically hotter because you are not getting the correct fuel wash on the piston crown.

Trust me, I use to have 2 strokes that idled and all ran 32:1. Neither situation is correct however.

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A properly tuned carb makes all of the difference in the world.

Spanky's 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 jettingisn’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.

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-throttlejetting 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.

Edited by KcDavis

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why would you want to jet your bike to run on a 24:1 mix when it is made to run on a 48:1 mix? all you are doing is using twice as much premix for no reason. but whatever floats your boat I guess..

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Thats what the guy said he had been using, so i went with it. I agree it is an ubeleiveable amout of oil.. Turns my $4.50 gallon of gas into $9.50 gallon of gas. Looks like im re-jetting! Thanks fo rall the info

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why would you want to jet your bike to run on a 24:1 mix when it is made to run on a 48:1 mix? all you are doing is using twice as much premix for no reason. but whatever floats your boat I guess..

Two stroke engines make the most power when they have more oil in the mix. It allows for better ring seal which helps promote higher compression in the engine. There is also more oil covering all of the parts which reduces the amount of loss from friction within the engine. There is a definitely a reason for running more oil in your two stroke engine, and it isn't just a waste of extra oil. The amount of oil you mix should be enough to leave a residual oil build up in the bottom of the crankcase after the engine has been sitting when you go to change the piston. If it's dry, you should add more oil to the mix, if it is around 1cm you are good, if there is a lot more, you should cut back. It really depends how hard you run the bike and where it see most of it's RPM.

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