Jul 21, 1999
My wife rides a 98 125EXC. I've done a lot of jetting on it but I'm not sure what's in there now. I went several steps leaner on the pilot and main and leaned the stock needle out. I was only after less spooge, though. It's still not cleaned up but it's 90% better. I doubt the spec would be a good one for you, though. She's not an aggressive rider and doesn't rev the bike much at all. I wouldn't trust it at extended high RPM's as I'm afraid it'd be lean.

I've been paying attention to KTM jetting posts since 98 and it's rare you'll see on for a 125EXC. You could try looking or searching here:


May 1, 2001
I have a 99' 125 EXC, live in Wisconsin at about 1000' elevation.

My jetting is the stock main jet, the top clip on the stock needle, and a 45 pilot jet, 6.0 slide.

I used to use a leaner main jet but switched back to stock after losing a crank bearing. I also tried a 7 mm slide, didn't like it, although it seamed to clean up the bottom in conjunction with the 45 pilot. Seemed a little lean though.

My bike runs slightly rich at 1/4 throttle but it doesn't bother me at all, I have never fouled a plug.

I use Golden Specto at 40:1-32:1, with 93 octane pump gas.


Apprentice Goon
Mar 16, 2001
Charlestown, IN
I don't know that jetting is going to obtain your objective. I mean, you probably should do other mods to get the bottom you are looking for like gearing, and reeds. Once you have your mods, then you need to jet the bike for the fuel/oil mix and elevation you ride. I think that bike has a 13/50 stock gearing...try a 52. Also there are reeds that are made to be better in different ranges of power. Carbontech is one brand I think that has these.
Most KTM's are jetted stock a little rich. With my stock settings I was running rich with every fuel combination. But then, I was also fumbling with Avgas.:eek:
I now run 110 octane with Mobil1 MX2T @ 40:1 500' ASL. I had to go from the stock 190 main to a 185, raised the clip to 2nd from top and it seems to be very nice now. Very little spooge. Nice light brown insulator. (00' 125sx)
But now I'm planning on messing everything up by changing my fuel/oil ratio to 32:1 (can't stand it being spot-on!) :D

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