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From all the way out. Mine from the factory was almost 3 1/2 in.
5.75 is a leaner slide, but we richen up the main and the pilot. The slide only affects jetting from idle to just under 1/2 throttle the same as the pilot and the main starts coming into play about 1/4 throttle so they all overlap and work together. FWIW I've been running the 5.75 and a 500 since 2018 and have 160 hours on that setup with no issues with only 2 top ends and 1 bottom end (I got bit by the bad VP fuel earlier this year).
I went with the 500 main and 32.5 pilot, the 35 was too rich I guess. I started with power valve at 1.75, went to 2. I will mess with it.
Bike runs better than it has with stock jetting or the keihin 38 with jd jetting. I just don’t think I like ktm 250’s. Last one I had was a 2003 250sx, after that it’s just been 300’s. It pulls good, very clean, pull the wheel up pretty easy, but there’s something right off idle to mid that feels like it’s weak sauce but I know it’s not.
Also try to go out with the power valve and see how it changes things. Instead of 1/4 turns go in 1/8 turns. When I replaced my bottom and top and this last time even though I mic'ed the gaskets I think the squish changed some and it had a slight hesitation almost bog feel on the bottom out of turns and I ended up 1/8 turn out from where I was and it was back to a rocket ship, so 1 5/8 turns in from all the way out. Bottom end isn't something these bikes lack so if you're feeling like its missing something off idle/down low I feel its just in the fine tuning.
My bike currently has the 32.5 as well. When the temps drop into the 40's I end up putting the 35 in it just to be safe and not run lean. In my experience if I leave the 35 in it when the temps go back to the 50/60's it will still run well, but I'll get a bog between jumps. Like in between a double double section, exactly where you don't want a bike to bog lol.
Hey, I have a 2022 TC 250 with the following (factory settings):
Main jet 450
Pilot jet 35
Slide 4.0
Needle 42-71
Clip position #3
Needle jet S-1
Air screw just not falling out
Fuel 1:40
I have a worn jet block gasket, ordered the new JD jetting in pair with the JD jet kit (TC 250 2017-2021)
I don't know that I need to change the slide and the needle jet for this kit? Because its only includes main idle and jet needles.
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JD kit is a bandaid that is designed to compensate for the whacky stock slide. The jetting in this thread is for when you decide you want to do it the right way. They are 2 different schools of thought that are not compatible.
Thank you, this is the answer what I cant find anywhere.
So I have a JDjetting for the 250 mikuni tmx 38 for sale in the EU. 😃
What you think the best setup for slow/normal trail riding with some fast straight WOT without forest trails on 100m elevation, 10-20 °C
Main jet 500
Pilot jet 32.5
Slide 5.75 (Kawasaki part#16025-0003)
Needle 43-75 (KTM part #55431134400)
Clip position #2
Needle jet S4 (KTM part #55431021400)
Air screw 1.5-2.0
Fuel 55:1
OR
MJ 490
PJ 32.5
AS 1.5 turns out
Needle jet S4 (KTM part #55431021400) stock is S1
Needle 42-75 on the 2nd clip (Yamaha part #284-14116-H5-00)
Slide 5.5 (Kawasaki part 16025-0002)
PV 1.75 turns in from all the way out
Fuel mix 50:1
The first one. Also adjust the power valve 1 3/4 turns in from all the way out and adjust in 1/8 turns in and out to see what you like best.
Main jet 500
Pilot jet 32.5
Slide 5.75 (Kawasaki part#16025-0003)
Needle 43-75 (KTM part #55431134400)
Clip position #2
Needle jet S4 (KTM part #55431021400)
Air screw 1.5-2.0
Fuel 55:1
Ordered the 5.5 slide before your reply, hope it will be ok.
Digger & FGR01, hoping to get your input with my case after having read your input on all other posts I can find.
Elevation: 6000 at home, 7000-10000 at typical riding locations
Riding style: woods/trail, single track; zero track
Bike: 2022 KTM 125 XC
Carb: Keihin 38 AS short body
Pilot: 48
Main: 180
AS: 1.5
Needle: JD red, position 2
Slide: stock 6.5; re-filed to 7 specs
When I roll onto the throttle the response seems OK, it doesn't hit hard by any means but seems to pull OK but could be stronger (comparing to my 2022 300xc and previous 300s & 250s i've owned). What I cannot seem to jet out with any combination is a bog and stall situation when I wack the throttle open. I initially thought it was rich when doing this but found it resolves when running choke or restricting airflow by stuffing my hand in the throat of the airbox.
I've changed jetting all the way up and down the spectrum from lean to rich with what I have available: JD red/blue needles, pilots 48/50/55, mains: 180/185/190/195. Going on the rich end (blue needle clip #4) makes it basically unridable, just dies with any throttle under load. Going leaner (red needle clip #2 or 3) seems to run the best. I filed the slide from a 6.5 to 7 spec and that did seem to improve things.
Based on this info do you think the leaner end of Diggers recommended needles (CCM or CEx) would be best or should I try FGR01's ultra lean N3CK (BEx)? I'm mostly confused by the overall better running on the leaner side but the bog and stall clearing up by richening with choke/reduced airflow.
The CCx needles were all too rich for me. But I stayed on 6.5 slide. 7 may just be getting too lean for a 125.
The filing of the slide actually seemed to improve response quite noticeably. I took it for a ride today after changing to clip position #3 and it actually felt pretty good today. It was on the cooler side this afternoon, about 50. I also noticed with this jetting if I quickly open throttle to 3/4, response seems great. Its just when I slam it to full throttle that it bogs out. Its getting close, I really feel like its a matter of finding the right needle for it and I just don't think the JD needle is it for my application.
@AJ565 @FGR01
I installed the following:
Pilot jet--32.5
Needel--42-75 #2 clip position
Main--500
Needle Jet--S-4
Slide---5.5,
air Screw---1.5
With this I got a lean bog at low rpm low throttle position (1/8) so I adjusted the screw and found the best where Its not too rich so not stall at idle, and not too lean so no lean bog under low rpm low throttle. Its air screw at 0.75. But I feel that it a bit richer now than 1/8 to 1/4 throttle, and feels that it leans out when the rpm goes up with static throttle begween 1/4 to 1/2. So in short, throttle at 0-1/8 can be good with Air screw 0.75 to 1 and its leaner but no lean bog etc, just feel that it can be richer from 1/8 to 1/2 and from 1/2 to 1 feels spot on. Test made at constant 100m elevation and 6 °C.
Any tips? #3 clip position or 43-75 needle?
Thanks in advance!
PS.: I think Mikuni messed up something at the point in the slide where there is a cutout for idle holes at the carb body, next to the jet needle.
The two holes in the body (the part where the sluggish gasket is) are in a wider position than the cutout width in the slide.
at 6C and 100M elevation I would be on 43-75(2) or maybe even 42-75(3) for sure. When my bike was a 250, at those conditions I was also on a 35 pilot and even 37.5 sometimes. But I was using a 5.75 slide, so adjust accordingly.
300 sxs
0m elevation , ~ 5°c
This is my jetting
520
37.5
43-75 2eme cran
S-4
5,75 slide
As: 1.25
I ride deep sand
What would you suggest for my -22 KTM 125 SX? Sea level. Temps below 20 degrees Celsius. Carb is the stock Mikuni TMX 38.
- Should I keep the 32:1 premix or change it?
- Should I keep the Castrol A747 / go with full synthetic / or does it matter?
- Should I change the stock slide to the Kawa 5.75 slide?
- If I would change the slide, should I use the current needle (42-71) clipped richer or change the needle (to what)?
- Should I experiment with the MJ and PJ?
It has a VHM piston, VHM head, VHM CDI (map 1), after-market exhaust, and a lighter flywheel(?). The seller raced the bike (A class) using a 25:1 premix, Castrol A747. He said it ran perfectly. I bought it with low hours because they gave up on the sport. The jetting they made for deep sand tracks near sea level elevation and raced in temperatures between 10 to 25 degrees Celsius.
The jetting it came with, on a hard-packed track, I noticed stuttered a lot, especially mid-throttle. In a few hours, the plug was black. It felt rich, too. Naturally, there's spooge with the Castrol A747, as my skills won't allow me to be on the pipe at all times. I changed the premix to 32:1, the needle clip from position 2 to 1, and played with the air screw, which ended the stutter but also introduced the bog.
In the lower temperatures, from 5 degrees Celsius to 15 degrees Celsius, it seems to run better on pipe the more AS is closed, but it also starts worse with a cold engine.
I also cleaned the carb, and jets, checked the gaskets and float height.
The jetting it came with:
MJ 600
PJ 35
AS 1.5
Slide 4.0 (stock)
Needle 42-71, clip 2
Needle jet, I haven't checked, probably S4
Premix 25:1, Castol A747
My current jetting:
MJ 580
PJ 35
AS I have been testing from 3/4 to 2.5 open
Slide 4.0 (stock)
Needle 42-71, clip 1 (clip 2 results as a mid-throttle stutter)
Fuel mix 32:1, Castrol A747
The specs listed for the 125's in this thread are based on relatively stock bikes. You've got a lot of different variables going on there. I can tell you for sure, you don't want to use a 5.75 slide in a 125.
I figured that out regarding the variables, but I'm kind of lost with my troubleshooting roadmap. The clip adjustment with the 42-71 needle acts like a 1 or 0. Clip 2 stutters and Clip 1 bogs. It feels like the range between them is nonexistent. I thought a leaner slide could introduce more "range" to adjustments, the stock slide being the richest of available slides. In Europe, the 5.0 slide is unavailable, so the only replacement slide I've found is the Kawa 5.75 slide.
Given my variables, would the 5.75 slide make things too lean? Or could you tell me if you're referring to stock 125? Do you have any other suggestions about what to do next?
The 5.75 is way too lean for a 125. Even the 5.0 is almost a little too lean for the 125 and you have to make sure the rest of the jetting is proper to make the 5.0 work.
If you want a simple answer to the needle dilemma and just address that directly, the 43-71 has grooves cut half-clip richer than 42-71. So, the 43-71 on clip-1 is essentially the same as 42-71 on clip-1.5. Basically splitting the difference that you're having the issue with.
Pit Row
Thank you! I'm not necessarily looking for an easy answer but a step-by-step roadmap. However, the 43-71 needle would be a logical step if the slide were out of the equation. How do you see going back to the 25:1 premix? Could that help? Given the bike mods, I don't have data on what most race teams use as their premix, but I think only a minority would use such premix. I could be wrong, though.
Could something like this sound like a logical roadmap?
1. 43-71 jet needle, Clip 1
2. If better, but not there yet -> PJ 37.5
3. If better, but not there yet -> 5.0 slide (if found somewhere), 43-71 clip 2 / 3, MJ 600, and PJ 37.5
Don't do the 5.0 slide unless you are going to commit to doing EVERYTHING in this thread. You cannot piecemeal it. Changing the slide has a drastic effect that requires all the other changes.
I can't really help if you're doing some other wild variations I am not familiar with. Too difficult doing it over the internet without being there to hear and feel the bike.
Update
I rode this saturday I was too lean, so I adjusted the needle, main jet and air screw
Sea Level, 2°celcius, lots of wind
Deep sand track (Loon-plage, FRANCE)
300 SXS 2018 with ovalized carburetor
MJ 560
PJ 37.5
AS 1.0
Slide 5.75
Needle 43-75, clip 3
S4
Premix 40:1, Motul 800 ( 50/50 Avgas/SP98)
Cool to see the changes that are required for an extreme condition like that. 560 main and that clip setting on a 43 on a 300 is wild. I assume the bike is not much good for slower, low throttle settings if the temp warms up. Suited for that WFO in the sand.
there is the sparkplug before the changes, too lean at mid en high RPM, the sound not good ( metallic) with this settings :
520
37.5
43-75 2eme cran
S-4
5,75 slide
As: 1.25
The photo below is with the jettings updates
Just got a 2022 Ktm150sx. Used to have a 2019 With JD kit and it ran good i thought but looking for the best setup i can possibly have on this one. Which way is more beneficial in yalls opinions, 1- AJ’s settings 2- Keihn 38 with JD kit or TSP kit?
Also is there any updated info about the 22 issue? Is it worth it to just get an older crank and put an older cdi on?
Do you know the history of the bike since new? Do you know if the recall was performed on it? How many hours are on the bike? You can tell if it has the older "good" connecting rod if it has 503 cast in it. If it does not, I'd put an aftermarket ProX or Wossner rod in it, unless someone did already.
I wouldn't worry too much about the CDI. You can try chasing down an older one but I don't think it's a huge deal. They also cost over $200 so you'd probably be better off getting an aftermarket one.
As far as jetting, I've done both the Keihin and the Mikuni jetting from this thread. I prefer the Mikuni as it can be fine tuned better than the Keihin. The TSP Keihin jetting is basically just the stock 2016 jetting. All things said and done, if you just want the bike to rip with the least amount of effort and are not a guy that doesn't mind tinkering with stuff, get the Keihin with JD or TSP kit. The jetting from this thread will dial the Mikuni in cheaper than getting a Keihin, but almost always requires some level of fiddling and tinkering to get it right. Some guys just don't have the feel to adjust jetting and get frustrated after the 10th time pulling the carb off the bike.. lol
It has 50 hrs and supposedly a new piston at 40 hrs. Its a single ring also. I just peaked into the exhaust port but the cylinder looks brand new/ vapor blasted so no telling what all has really been done. Might look up the VIN and see what it says as far as the recall goes. I guess ill just leave the CDI alone too. Ive currently got the stock mikuni running clean but feels lean and weak on torque compared to my 19 with JD kit. Im 800ft, 45-60F and tried jetting per the manual 42-71/ 3rd/ 480/ 32.5/ 1.5 and had rich sputter mainly in the middle it felt like. Went to 42-71/ 2nd/ 470/ 30/ 1.5 and its clean but gutless on the torque and too on/off so i know to be happy with it im gonna have to just spend some money. I don’t have a ton of experience with carbs but i know every bike ive rode with a Keihn has been great. Used to have a 200xcw with a lectron and a buddy had the same bike with Keihn JD kit and it was so much more responsive. Just sold a 2024 yz250x and loved that with the Keihn and power jet. Ive had 2 17 250sx’s and both hated the mikuni power delivery/ responsiveness. The Keihn and JD kit sounds good to me i think. Im going to be riding woods, racing hare scrambles mostly with it and won’t be wide slap open like moto very often so as long as it pretty close to spot on with the Keihn and JD kit then i think ill be okay with it because the 19 i had only had the JD kit and it felt pretty decent. I appreciate the info!
Honestly don’t want to take it apart to check out the rod lol Im thinking just get the carb deal sorted and rip it till Feb/ March and rebuild with older oem crank and piston before the season starts.
After some thought im gonna try to stay with the Mikuni. Im about 1000ft elevation. Couple more questions i have. Where can i get the 510 main? Should i go ahead and notch the #5 slide when i get it and go with a 30 pilot? What temps will the current recommended specs be good in? I have 30-32.5 pilots/ 470-480-490 mains already. Gonna be riding in 40f-60f for the next few months then after that 60f-90f.
I never notch the slide and have always gotten bikes to run great. Start here:
Fuel 40:1
Slide 5
Needle jet S-4
Needle 43-75, clip 2
Pilot 32.5
Main 510
AS 1.5-2.0
It will likely require some fine tuning. Maybe the 42-75 on clip 3, maybe 30 or 35 pilot, and maybe smaller main down to 490-500. But that is where I would start.
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