Carb/throttle sticking issues - cant find cause?

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KTM Mike
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Carb/throttle sticking issues - cant find cause?

Post by KTM Mike »

My son's KDX has had some issues with the throttle sticking over the last couple of years. I have had the throttle apart cleaned and inspected it, replaced the cable, had the carb apart multiple times - can not seem to find any likely cause. i must admit, I began to think maybe it was operator error - but know it isnt as I have had it stick on me as well.

Throttle seems to stick in various positions - 3/4 open, 1/2 or less etc. Most recently was at a smaller throttle opening, and according to my son, he was only very lightly accelerating if at all - yet it started pulling like it was opened up.

Where should I look next? Could this be reed valve related somehow? Air leak? (main seal maybe?), some other issue I have not stumbled onto with the various times I have had the carb, throttle etc all apart? I am considering simply replacing everything from carb to throttle just to rule that out..but that is expensive.

Any suggestions appreciated.

Oh - I found out I cant change my email address here to my new address (a gmail account) - so I wont be getting email notifications of replies.... so there may be a time lag before I can respond back
Ok..so why is KTM MIke on a KDX web site? My son has a KDX - nice bike to.!

2005 KTM250EXC (mine)
1999 KDX200 (kid')s
2003 KTM 200 MXC (the other kid's)
1976 Penton 250 Cross Country (built back when men were men, and trees were 36" apart!)
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Indawoods
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Post by Indawoods »

By your sig I can tell you are no newbie!

But, I have to say... your not lubing it are you? Some people make that mistake.

Is the cable routed as the manual shows? This is very very important.

An air leak will cause high revs if you can rule out the cable sticking as your boy stated.
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KTM Mike
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Post by KTM Mike »

Inda - nope, not a newbie here. New cable though...not lubed (unless my kid did...but I dont think so)

As far as I know, routing is as it was stock - but I will double check that to be sure - good point. It seems it sticks when wheel is straight on though - not when turned (my Penton has issues when the wheel is turned if I misroute it...I learned that the hard way)

The air leak idea came to me as he described the fact this last time it stuck, he described he had chopped the throttle for a rough bit of trail or something, had rolled back on very lightly (he says 1/8 throttle - only lightly accelerating), throttle then stuck and the bike accelerated as if he had wacked it wide open. It just did not seem to make sense to either of us. It is not like my kid is a totally newbie either - has been on bikes for 10 years already (since he was 5), and rides regularly - so not a typical newbie panic throttle roll on, or over reaction to the bike coming up on the pipe.
Ok..so why is KTM MIke on a KDX web site? My son has a KDX - nice bike to.!

2005 KTM250EXC (mine)
1999 KDX200 (kid')s
2003 KTM 200 MXC (the other kid's)
1976 Penton 250 Cross Country (built back when men were men, and trees were 36" apart!)
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Indawoods
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Post by Indawoods »

Might check the petcock to see if your getting fuel starvation also...
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****'95 KDX 200/****

"People ate cows a thousand years ago for the same reason we eat them now. Cause they are easy to catch.We're not savages,we're just lazy. A cheetah could taste like chocolate heroin. But will never know. Those bastards are fast!!! "
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Colorado Mike
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Post by Colorado Mike »

The downside of not attending to an air leak is costly enough to warrant rigging up a leak-down tester. I made one out of stuff I got at Home Depot and such for well under $20. Mr. Black suggested expandable freeze plugs for the intake and exhaust holes. That would work better than my exhaust port plug which was a cave-manish PVC end cap with a piece of innertube over it clamped in place.

I cobbled up an intake plug out of another PVC fitting that I turned to the proper diameter on my lathe, then just installed it as though it was the carb. That had all my fittings threaded into it, a shrader valve and the guage.

You just need to inflate the cylinder / case to about 7 psi, and watch that it doesn't lose that too quickly. I used a 0-30 psi dial guage I had laying around and some NPT fittings.
Mike

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'04 KDX220
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canyncarvr
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Post by canyncarvr »

Something simple? A loose barkbuster end will get you interference with various bumps and crashes.

A leak is quite different from a stuck throttle. The former is more a weak, no power sort of wisp. Not always a simple thing to tell which is which..not when the thing is stuck!!

I've had a few 'issues' with throttle-sticks on Banshees. A WOT stuck 350cc 2T twin is exciting!!

The 'couple year' part and what you've done so far kind'a precludes this...but has your 'all apart' included unclipping the throttle cable from the curved tube at the top of the carb? Cables fray at that bend..and you probably won't see it unless you take the clip off the tube and completely remove the cable from the carb cap.

All of that most likely having nothing to do with it at all..having replaced the cable and such. Still...it might be more than one thing?

Note: The throttle cable does run kind'a wide coming out of the cap. It looks like it'll get snagged on something..but running it INside the coolant hose don't work a'tall.

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KTM Mike
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Post by KTM Mike »

Thanks everyone - we will be tearing into it (again) tomorrow - I will post back what we find. Plenty of good suggestions here.

One more bit of help we need though - I hate to admit it, but I dont have a factory service manual for the KDX (99 200) as I have just borrowed a friends when needed.... so I dont have pics to verify cable routing with. Can someone post pics, or perhaps describe in detail proper routing? (my buddy is out of town so cant get his manual!)
Ok..so why is KTM MIke on a KDX web site? My son has a KDX - nice bike to.!

2005 KTM250EXC (mine)
1999 KDX200 (kid')s
2003 KTM 200 MXC (the other kid's)
1976 Penton 250 Cross Country (built back when men were men, and trees were 36" apart!)
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canyncarvr
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Post by canyncarvr »

Image

..and

Image

Note on the first one the throttle cable goes on the OUTside of the petcock and the coolant hose..

and on the second one the throttle cable goes FORWARD of pretty much everything..the brake and clutch.

Any help at'all?

Of course...these are pics of MY bike..and someone will be sure to point out that I've got it all wrong.......... :oops:

But it don't stick! :wink:

Note the extra hoses on the carb. It's a 4-vent air striker. There's more room with the OEM PWK.

Oh...notice how squeeky clean my carb is? That must be 'cuz I power-wash the hell out of it every time I go riding, 'eh? :wink:

Well, maybe not........

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Rob
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Post by Rob »

My throttle cable is routed behind the petcock.

First thing I notice is lack of an inline fuel filter. The D shaped slides in these carbs are extremely sensitive to even the tiniest specks of dirt. At partial throttle openings there is a very powerful vacuum pulling/pushing the slide against the inside of the carb. Mine has stuck "open" a number of times -almost exclusivelyl after running through deep water -getting the filter wet which then washes a few grains of sand through it and right into the carb. Just one of those sharp little grains getting on the backside of the slide will lock it in a very undesirable position. Remove the drain from the bottom of the carb and see if there's any dirt down in there - which will work it's way up into the airstream. Aalso make sure the filter is clean and well oiled or dust/dirt/sand will migrate thru. I seal the filter to the airbox with marine grease and coat the inside of the airbox with the same grease to hopefully "snag" any stray dirt particles travelilnlg through.
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