KTM Newbie

Jul 9, 2001
I have a 2001 KTM 250 MXC that I bought about 2 months ago. I usually only ride for a considerable length of time on the weekends, sometimes 25 miles or so. So far, I have fowled 3 spark plugs beyond repair. I have heard that due to the 30 day guarantee with KTM, the tell the dealers to set the bikes up lean so you can't blow the motor, thereby making KTM pay for it.

Is this true, and how do I fix it?

By the way, I love the bike and and the power is perfect for my novice way of riding, but I can't have another day of walking 1.5 miles in 102 degree temperatures in full gear due to a fowled plug.


Mar 7, 2001
Actually the factory usually sets the bike rich so it won't blow the engine. Lean bikes don't generally foul plugs. Also the type of mix oil you use makes a difference. Do a search here for mix ration and fouled plugs, the subjects have been covered several times and there is tons of information. Unfortunatly much if it is subjective and there are guys here running a wide variety of different oils and mixes with good luck. I started running Honda premix oil at 32:1 and wasn't fouling plugs. I switched to a type of oil that (susposedly) has better protection and was fouling plugs until I switched to 50:1 (At which point I'm sckepitcal the extra protection is doing any good with that much less oil)
Also your riding style can have an impact. When I trail ride I foul plugs much more often than when I ride on a track.

Mark C.

Posts Too Much
Nov 1, 2000
What ratio are you mixing the oil at? Also are you riding the bike at low rpms ( trial riding mainly ) or are you on the gas mostly. If your running the bike at really low rpms ( low speed ) then you may wanna try a hotter plug ( go down 1 heat range on the spark plug ), then do a spark plug test. Tan = perfect, wet black looking = running rich, and white insulator = lean. Reply with answers please.....:)


Apprentice Goon
Mar 16, 2001
Charlestown, IN
Only time I've ever fouled a plug on my KTM was when the mix had settled in the tank and tube and I didn't shake the bike up before I started it. If this happens, you can start...take off...ride a piece and RRRrrrrrrrrrr,.......Done.
Cold fouled. Make sure you are shaking your bike and keeping the oil mixed.
I would imagine you being a bit rich, but can't imagine you fouling a plug just because of oil choice. I think that bike has a pwk 38 with a 180 main jet.
Take a look at your plug after getting on it pretty hard WOT. If it's black(insulator...look deep inside it) , I'd suggest going to another main, somewhere between 175-179. You may also need to raise your needle clip up one notch to second from top. Be sure you arent using any fuel out of uncle Johns farm tank. Isn't Houston like right at sea level? I think KTMs are factory jetted for 1000' ASL.
I have a 125, and I can rip it up or putt around all day and never foul a plug from just riding conditions or oil choice.(450' ASL.)
I'm running 110 octane @ 40:1 w/Mobil1 MX2T


Here are the stock settings:

  • 178 Main jet
  • 45 Pilot jet
  • Needle clip-3rd position from top
  • Air screw-1-1/2 out

Here is how my dealer told me to set it up:
  • 175/172 Main jet
  • 42 Pilot jet
  • Needle clip-2nd from top
  • Air screw-1-1/2 out

I have two days of riding and several warm-ups in the garage and have only fouled one plug (first day in garage) because I was cranking the throttle on start up.
My cold starting procedure: Choke on, two slow priming kicks, then I kick it like I mean it and it starts first real kick 90% of the time. Second kick tops. Turn the choke off almost immediately and blip the throttle to keep it running. I don't ride off until there is warmth to the radiators.
I only got the jets changed last night but moved the needle clip to the second position prior to the first ride. Even with stock jetting, I had no problems starting or with fouled plugs on my first two rides.
When warm, I just kick it and it starts right up.
Going on what my dealer has told me, I would lean it out a bit for sure. There are a lot of KTM jetting savy members here who can offer a load more info than I can (Strick, Jeb & the GrandMaster-James Dean) I'm sure you'll get some help here before too long.:)

Also-Go here: http://www.ktm-racetech.com/ and click the "Message Board" button and then browse their "Jetting" forum. Lots of great KTM-specific info there.
Last edited by a moderator:


Sep 8, 1999
01 250 jetting

Good jetting requires some experimentation on your part. It only takes a few minutes to change the jets/needle/clip position. Get a 40 & 42 pilot, a 170 & 172 main and the next step leaner needle. My EXC came with 172,175,180 mains, 42,45 pilots and NOZG,NOZH needles. I live in Illinois at about 700 ft and was running a 40 pilot and 172 main with the NOZH needle in the middle clip position. This worked well enough in the woods at low throttle settings and no fouled plugs. I'm currently riding in Colorado at altitudes ranging from 4,000 to 13,000ft and temps from 80 to 50 degrees. On the first day here I rode to an elevation of about 10,000 ft. The bike was running very rich everywhere. I stopped, got out the tool kit and changed jetting right there. Put in a 40 pilot, 170 main, moved the needle clip one position leaner and put in a fresh plug. The jetting is still a little fat at altitudes above 9,000 ft but it 's close enough below that. The point is that if you just let others advise you on what jetting to run you'll never learn anything and will probably need to start buying spark plugs in bulk. A final note, and none of this is meant as a personal attack. Only fools ride without tools. At least take a plug and plug wrench along.


Mar 15, 2000
Should be a jetting chart in the back of your owner's manual. With really hot conditions, you should be jetted leaner. Also, we have had luck dropping the float level by 5 to 8mm and using the jetting recommended on the chart.

Haven't fouled a plug in 4 years, change em every 6 months or so.

Let me know if you need the jetting chart from the 2000's, I'll email it to you.

General rules for jetting, the leaner (smaller jet numbers) the more power the bike will make and the less chance for fouling, but greater chances of melting down the motor. Rich jetting is the opposite.

Remember that Higher, Hotter, and more Humid (HHH) requires smaller jets...

Change all three jets, the slow, the needle and position, and the main.


Dec 8, 2000
250 jetting

Try this jetting: 45pilot-11/2 turns out on air screw-1369needle-175main You can get this needle from Sudco 1-800-998-3529 the needle is a CEK (1369) I have this jetting in my 01 250 exc and it runs great, crisp and clean from bottom to top. This needle is about $8 Almost forgot needle in 3rd. notch from top.

KTM Newbie

Jul 9, 2001
Thanks Guys

Wow, I wasn't expecting this kind of response.
Anyway, I have taken the bike to a shop and they fixed it. I runs like a whole new bike, thanks guys.


Sponsoring Member
Mar 7, 2000
That doesn't help you if you don't know "how" they fixed it. KTM's are temp picky and come winter time with that cold coming off the ocean, you'll need to be re-jetting possibly. Not to mention the Houston humidity....whew!!!!!!!!!
Please post your final jetting:
Needle: and what clip
Air Screw:
Oil: and at what mix
Silencer: Got that bazooka off yet?


I agree with Yarbo,

It's no fun if you don't know how to do it yourself. Plus you get to pass on your acquired knowledge to others. I have been studying this KTM jetting thing for a couple of weeks now and it is quite the learning experience!

Latest experiment: Adjusting the airscrew for each ride after warm-up. Turn airscrew in until engine starts to stumble, then turn out until the highest RPM point is reached. If pilot jet is correct, this should be in the 1-1/2 to 2 turns out range. This is supposed to give a fine-tuning to optimize throttle response. Anyone else doing this?

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