Mar 4, 2000
My friend has a new 2001KTM that keeps fouling plugs. The bike always has spark and the carb. is set-up correctly (40:1 Champion pre-mix). Is there something common to this model that may cause this issue. It is like the early 70s bike....i.e. this kind of thing should not be happening for a modern bike.:think


Jul 11, 2001
What do you mean the carb is set up correctly? If it's fouling plugs, it's probably jetted too rich, and that has nothing (significant) to do with the fuel-oil ratio. Get the bike jetted correctly, and it will probably stop fouling plugs. Also, once it has fouled a plug, don't try to clean it off and re-use it. KTMs are very intolerant of that nonsense. Just get a new plug in there and save yourself the aggravation. Do a search of "jetting" in this forum and you'll find a wealth of information.

If the bike really is jetted correctly and still fouling plugs, you could have an ignition problem, which seems unlikely on a fairly new bike, but it's worth looking into.


Cloverdale-A couple of questions:
1. Does it start and THEN foul the plug, or does it foul the plug while trying to start it?
2. Which model is it: EXC, MXC or SX?
3.What is your elevation?
4. What is the current carb set-up? (Pilot jet, main jet, airscrew position and needle clip position)
List the answers to these questions and I or many others here can help out with some basic info.:)

Mr. Mark

Jan 6, 2000
A friend of mine has a `00 250 E/XC that fouls plugs like
crazy. He's re-jetting to normal summer specs but still goes
through a plug per ride. I think he found the float was bent
(the two floats were not even with each other).
I haven't heard if this fixed his plug fouling though...



Mar 12, 2000
I have an 01 250 EXC and although its not jetted 100% perfect, I have put over 300 miles on it in the last few weekends and it is still on the original plug. As far as I am concerned, I am still too fat. NOZH #2 (fat) 175main, 45 pilot stock 6.5 slide. 1000 ft ASL 60-80 degrees F.


I'm right there with scotty. >1000 ft. ASL, 42 pilot (45 was stock), 175 main (178 was stock) NOZH #2, 1.5 out on airscrew. No fouled plugs since new in late June.


Sep 8, 1999
Just got back from a weekend riding the tomahawk trails in northern michigan on my 01 250 exc. I rode there with the guy Mr. Mark refered to who rides an 00 250 exc. On Saturday morning he fouled a plug at start up. This has been the typical routine all season. Just before this ride he went through the carb and did a thorough cleaning to eliminate any possibility that an air or fuel passageway might be plugged. On Sunday morning the bike started and ran fine all day. I rejetted Saturday morning because the temps were mid sixties to low seventies and the last time I rode temps were in the mid eighties. I rejetted to 42/175/NOZH#3/6.5 slide. The bike ran good with just a little blubbering at the 0 to 1/8. He ran 42/175/NOZI#2/6.0 slide. His bike ran nearly the same as mine even though he ran a leaner needle in a leaner clip position. It must be a combination of the 6.0 slide and the redesigned cylinder that accounts for these differences.

As a final note if you have the opportunity to ride this trail system don't miss it. The sand was moist from the rain the night before on Saturday and traction was unbelievable plus zero dust. It rained on Sunday but we did 40 miles anyway and had a blast. These trails have some of everything from tight woods to WFO straight sections and of course scenic views everywhere.


Jul 2, 2000
I have an 01 250 exc and mine was fouling plugs like crazy also. I had to rejet 6 times until it was right. It is now at 170 main, 40 pilot, NOZH clip position #1, stock slide. It runs great and no more problems. I am going to go to a NOZI and start the clip at #3. That may give me some range to play with as the temp changes. Once it is jetted correctly, the bike is much stronger on bottom and mid. A FMF turbine core 2 also helped my bikes power and ease of jetting.


Apprentice Goon
Mar 16, 2001
Charlestown, IN
I am suspect of these "at start up" fouls. I'd first make certain that you have shaken the bike real well. Not doing so can result in oil settling in the bottom of the tank and in the tube(I've found spectro synthetic to be bad about seperating in cold temp). This can cold foul a plug real fast, and have nothing to do with proper jetting.

Just an item to check.


Jan 5, 2001
The 2001 SX has a powerjet carb. When this system fails or is unpluged it will go "full rich". The only way to eliminate the power jet is to close off the the jet itself. An easy way to check that your powerjet is working is to unplug the wire and put a test light to the wiring harness side and start your bike. You must have power from 0-6300 rpm's and from 6300-8500 there must be no power (the system is working and allowing fuel flow). Above 8500 there must be power (the system is shut off and running on normal jetting). I hope this gives you something to check for.
Last edited:


Dec 8, 2000
01 jetting

guys try this;
175 main
45 pilot
cek needle#3
A.S 1-1/2
The cek needle is from sudco. #1-800-998-3529
If you have knocking you will have to run 50-50 mix of pump and race gas
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