Sticking throttle on KDX200

Work your throttle while turning the forks to all positions. Sometimes the cable will bind only when the steering is at a certain position. Also, if you haven't already, open up the throttle and make sure the cable inside is in the right position and there is no sand or grit inside. Also, slide the thropttle off the bar and make sure no sand or grit is inside the throttle tube. Lastly, inspect the place where the cable enters the carb. Sometines the cable end will jump out if something is worn and there is not enough tension to hold it in.

Lube The Cable

Sounds like you think the problem was in the air intake system. You have cleaned it all and then the filter again and again. Why not throw the filter away and start over? Oil a new one good and use grease to seal it where it meets the air box. I suspect your cable may have sand in it also. Might take a new one. Cheers John

Green Hornet said:

Lube The Cable

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Yes. At the risk of stating the obvious, disconnect the cable from the slide first, or else the pressurized lube spray will just push whatever dirt is hiding in the cable right into the carb slide.

If my throttle got stuck, I would have disassembled the throttle assembly and the carb immediately upon getting home. I would be looking for sandy grit and for wear marks on the slide and carb body. And of course clean the heck out of everything.

rocketman1 said:

Yeah I have cleaned it up now 100% and have no more problems, boy! I don't want that problem again!
I would say keep your air cleaner CLEAN and oiled and make sure you dont dislodge any sand into the carby side of the filter, when removing the filter. I did also reposition the throttle location a bit and it seems to snap shut a bit quicker , but I dont think this was the problem.

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I have to ask, when you noticed this sticking was it usually on a steep hill? If so, are you sure it was really stuck? Improper float level adjustment may cause a lean condition on longer steep hills which may cause a temporary "lean runaway" scenario.... Just a thought.

The throttle tube was pushed in on the bars.

That's my guess.

Rotor

ridejunky said:

I have to ask, when you noticed this sticking was it usually on a steep hill? If so, are you sure it was really stuck? Improper float level adjustment may cause a lean condition on longer steep hills which may cause a temporary "lean runaway" scenario.... Just a thought.

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It seems you didn't read this. Sounds logical to the problem you explained.

rocketman1 said:

What you say, I cannot quite understand, yes it only seems to stick badly going up a steep bumpy hill, fast.
Shutting the throttle to off position on the throttle grip makes no difference, it just screams away like a crazy thing, by flicking the throttle doesnt fix it. You have to hit the kill switch, start it up and she's sweet for the next few hours steep fast hills included, then, out of the blue it will scare the sh-t out of you again.
Can you please explain this lean runaway scenario as I dont quite understand what is meant by that & how do I adjust / fix it.
I know the previous owner adjusted the carb to make it run leaner, and make it a very snappy/ sharp throttle response, which it is, prior to that it bogged down a bit, he said it was running to rich, would this have anything to do with it?

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What you are describing has all the symptoms of lean run away, adjust your float higher so your bowl has the correct amount of fuel when ascending steep hills and your problems will disappear. You also may want to check to make sure your petcock is clean, this alone probably won't cause the problem but it may be contributing. Lean jetting is not the culprit.

rocketman1 said:

I trust what you say, but I have never heard of a lean runaway situation, but checking out the internet, it appears it is quite common, on aircraft engines, I was wondering does anyone know why a motor should want to self destruct itself in this fashion thank god for the kill switch.
What are the mechanics/ physics behind it all?

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The kill switch wont work!! BTW air leaks in carb boot can cause this situation too, most often it happens more consistently though. Think diesel andyou'll understand why the kill switch doesn't work

rocketman, can you answer the following question for us: when you say "throttle stuck open" are you really sure that the throttle slide itself was stuck in the open position? In other words, when you rolled off the throttle, did it feel like the silde was closing? Or did it feel like the spring which is supposed to push the slide down has somehow disappeared? We know your motor was revving high, but what did your right wrist feel? I'm probably asking a lot of you to analyze exactly what was happening in that terrifying moment, but the answer is really important.

rocketman1 said:

When I rolled of the throttle it was completely as normal...

It felt like the spring was not closing the slide.

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These 2 statements are contradictory. If it felt "normal" to your right wrist, then the spring did close the slide. So is the 2-nd statement describing what your wrist was feeling, or is it describing your guess of what caused the engine to rev? Assuming the spring really closed the slide, this leads us to the "lean runaway" described by ridejunky.

rocketman1 said:

What are the mechanics/ physics behind it all?

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I have my carb apart at the moment, so I tilted it as if on a steep uphill, and here are my observations. First of all, the jets end up sitting in a shallower pool of fuel because the float bowl is severely tilted. This is the beginning of a lean condition. However, leverage on the float needle is decreased, so this may compensate a little by allowing more fuel flow into the bowl. When you're running at WFO for a while, the fuel flow rate may become an issue depending on potential restrictions in petcock, fuel filter (if you have one), and float needle. Oh BTW, how much fuel did you have left in your fuel tank? After 3 hours of riding I bet you were running a bit low. If the float valve and/or needle side surfaces are rough then the needle may drag and not open all the way on a steep bumpy hill. Simply put, if the engine is able to consume fuel faster at WFO than the bowl gets refilled, then eventually it will get really lean. So it's very important to start by making sure your float bowl fuel level is correct.

Pilot jet is towards the front of the bike, so it will experience even more lean-out due to tilt. Don't forget that the pilot jet is always delivering fuel regardless of throttle opening. If incline is really steep, the pilot jet can be completely in the air, so now the overall mixture gets even leaner. If your bike was jetted a little on the rich side, this tilt-induced leanout will result in more power.

So you roll off the throttle hoping to calm the bike down. But a strange thing happens if tilt-induced leanout was too extreme: partially rolling off the throttle will bring air/fuel mixture back to ideal, thus producing more power. Now you are really scared and peeing in your pants, and you shut the throttle off completely. Does the idle stop screw really allow the slide to close completely? Usually not. If your pilot circuit is not set up quite right, then you probably turned the throttle stop screw clockwise so that the bike will idle OK, but this means that even with closed throttle it will draw some air under the slide and some fuel thru the main circuit. But on the hill the mixture is already very lean, plus the bike may be sucking air thru the pilot circuit instead of fuel, so the bike revs much more than expected for such a small throttle opening.

My bet is that when this phenomenon happens, riders don't really shut the throttle off completely because they are caught off-guard. Especially on a steep uphill the unexpected burst of power throws you back, and naturally causes your arm to pull the throttle open.

BTW, running lean for a while will make carbon deposits in the combustion chamber glow red-hot and ignite incoming mixture, so like ridejunky already pointed out, even killing the ignition may not always help.

I would do the following: (1) check float level. (2) buy a new float needle. (3) check condition of float valve and if it is rough then maybe you can polish the walls, but avoid touching the seat. (4) make sure floats don't stick when tilted to extreme angles. (5) always ride with 1 finger on the clutch lever.

rocketman1 said:

My thoughts against a full lean runaway condition is reinforced by that fact the kill switch worked on both occasions, surely this would not happening, if there was this self igniting deisel effect?

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Absence of self-ignition does not rule out lean runaway. Self-ignition requires carbon deposits or other sharp edges to be heated up by very high combustion temperatures for a long enough period of time to make those deposits glow.

Good luck, and keep us updated.

From what you were describing, I was almost certain that was your problem, now you can ride with confidence knowing you wont starve your float bowl and you bike wont scream away with a mind of its own.

Rocketman, 6mm is a huge discrepancy in float level, and certainly is a prime suspect. It might be worth a call to the previous owner to find out why he set it up this way. Maybe the floats are leaky and were not shutting off the fuel flow properly?

The manual describes 2 methods for checking the float level. The easy way with the carb removed is to measure height of float just as the tang touches the float needle. The harder way is to use an adapter which screws into the bowl drain, but it measures the actual fuel level. You might want to use the 2-nd more reliable method.

Also keep in mind that raising fuel level makes all circuits run richer, so you may need to revisit jetting.

Now that you corrected the float you will need to re jet to get it to run better. What is your clip position? sounds like you may want to drop your needle by raising the clip. I go 2nd from top then jet accordingly. There is alot in info on jetting if you do a search. Jet it to the way it suites your ridding style best.