2001 KTM 520 MXC, Correct Jetting for Elevation?

I have a 2001 KTM 520 MXC. A few months ago, I moved from ND (1,000ft elev) to CO (5,000-10,000ft elev). The bike carburated perfectly in ND, but I noticed that my bike developed a hiccup/sputter/hesitation around 1/8 to 3/8 throttle when I came to CO. The problem is not very noticable around 5,000ft where I live, but becomes a lot worse when I go riding up in the mountains around 8,000 - 10,000ft. I was running a 165 main in ND, then I tried a 162 then 160 in CO, but neither cured the sputter at 1/8 to 3/8 throttle.

Is it reasonable to hope that I can find a single setting that will work well in the wide elevation range from 5,000 - 10,000 ft? I don't feeling like swapping jets back and forth too much.

These are the stock settings:

Type: MX-FCR39

Main: 175

Jet Needle: OBDTM 2nd from top

Pilot: 48

Main air jet: 200

Idling air jet: 100

Starting jet: 85

Mixture screw: 2.5 turns out

These are the current settings:

Type: MX-FCR39

Main: tried 165,162,160 in CO, was good in ND with 165

Jet Needle: OCEMN 4th from top

Pilot: 48

Main air jet: 200

Idling air jet: 100

Starting jet: 85

Mixture screw: 2.5 turns out

I am thinking of turning the mixture screw in to lean the jetting, but I'm not sure if that's the right approach to cure the hiccup at 1/8 to 3/8 throttle. Any help is appreciated. Thanks.

there is no jetting that covers 5000ft of range but you can make it rideable.

go to-

155 main jet

200 main air jet

EMp needle

clip 3

45 pilot jet

100 pilot air jet

1.75 turns fuel screw

Thanks Eddie. I appreciate the help. I am planning to go into the shop this week and pick up the 155 main and 45 pilot jets you suggested, then I will adjust fuel screw to around 1.75.

For the time being, I have moved the existing needle to the clip 3 position and turned the fuel screw in from 2.5 turns out to 1.0 turns out with the 48 pilot and it helped a lot.

Is my OCEMN needle completely innappropriate? What is the difference between my current OCEMN needle and the EMp you suggested?

Again, thank you very much.


5th Letter!! last letter is the range from idle to 1/4 throttle, each leter down the alphabet is 1/10mm larger thus leaner (those are very very fine increments) with the exception that they skip O (oh) as it looks to much like 0 (zero) so you started with an "M" when you went to OCEMN "N" is one leaner than "M" (for that idle to 1/4 range) Eddie's recomendation of "P" is 2 steps (still pretty conservative) leaner as the selection is "N", "M", "P". (Note when he said "EMP" he is ignoring the first 2 letters so OCEMP)

Your question "is OCEMN in appropriate?" That is a very good needle for low elevation.

4th letter is the distance from clip to start of taper, I don't dwell on this as i can work with any of them

3rd letter is taper angle, "D" is very shallow angle and "E" is very steep (JD is in between? Or more corectly is "E" part way and then changes to "D"). What makes this a big deal is "D" is so fat at the tip that it partailly blocks the flow of the main jet so main jet sizes are bigger with the "D" than an "E". If you where still a flat lander I would say when you changed from OBDTM 175 to OCEMN you needed to go down to 160-162 area to compensate for the needle taper and now it is a little richer in hte 1/2 to 3/4 range where the "D" taper has always been lean.

I like to set bikes up a bit lean in the idle thru 1/4 range for good throttle control then richer in the 1/3 to open range to cool the engine when you get on it so I would look at

45 pilot, OCE?R and about a 155. As I am not picky on the 4th letter, to set the clip set a micrometer at .104", drop the needle into the mic until it sticks, measure up 2.6" and put the clip there.

If you come down off the hill put in a #48 pilot (note this is for the 2000-2002 carb, 03 & up need a #42 pilot) and increase the main to 160ish

To go up on the hill

Thanks Dave, I appreciate the description of the 3-4-5 letters in the needle code. It is nice to learn a little more about jetting so that I can do it myself instead of paying somebody $60/hr to do it for me. Thanks.

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