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The notch in the slide makes the bottom richer. You typically need about 2 sizes smaller on the pilot jet compared to no notch.
Quick update. I repacked the exhaust, put in a fresh plug and kept the 27.5 pilot. Ran it around for about 10 minutes and looks like I may be good. Here is what my plug looks like. At some point I was really rich based on how my piston looks. It looks washed.
i'm driving elevation 700-900Ft. Temperature 60-70°F.
I honestly can’t feel the power difference between a 460 and 500 main jet. Needle 42-75 3 position. Slide 5.5.
where is the problem?
What kind of bike? What's the rest of jetting? Did you change the needle jet and the pilot?
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KTM sx 250 2019
Main jet 470
Pilot jet 32.5 (60-80°F)
Slide 5.5
Needle 42-75
Clip position #3
Needle jet S4
Air screw 1.5-2.0
Fuel 50:1
Put the 500 back in. Did you adjust the power valve?
Thanks!
PV Yellow spring 2 turns in from.
Put the stock sping back in and set it at 1 3/4 turns in from all the way out and adjust from there in 1\8 turns. Try 1/8 out first and see if that improves things. I noticed on mine after I replaced the bottom end that I had to adjust my PV from where I had it set to get the power back to where it was before the rebuild.
I have a 2019 250 xc and am interested in this jetting. I can get the kawi slides at my local Rocky Mountain, i would like to do the jetting with the 5.7 slide, but intend to eventually put a 300 kit and the 300 jetting you have uses the 5.5 slide. Question is, how much difference in the 2 jetting for the 250? I do run on the pipe some, would i even notice the difference in the 2?
Oh, and what elevation/temp is this jetting for?
I think that 300 jetting that's listed on page 1 was a little light on the development. I have ran both the 5.5 and the 5.75 in both 250 and 300. The 5.75 is definitely better than the 5.5 for the 300 and, in my opinion, better in a 250 as well.
The jetting from 250 to 300 is not much different at all, actually. I'm only about 1/2 a clip leaner on the needle and 1-2 sizes smaller on the pilot when I went to the 300. If you get the jetting from this thread working well on your 250, it won't be massive differences when you put on the 300 kit.
I dont know man, i took the mikuni off and got the keihin 38 with jd jetting, i went up and down and couldnt get it right. I replaced the mikuni mid body gasket, set float height to about 8.5(it was like 11) and drilled the drain cap and splash guard and it seems its better with 43-75(2), 27.5, and 450. Thats a little leaner than the ktm jetting chart. I’m going to check the keihin float, but not sure trying to jet around the jd needles works for me. Not sure what needle to use. The problem with the jd keihin set up is its feels flat and the annoying pipe bang/decel surge is bad. I put the mikuni back on yesterday and its way better. When i took it off originally the mid gasket was really jacked up and the float was pretty high. I’m going to give the Kawasaki slide a try. This bike fyi is new to me, a 2019 250xc that only had 7 hours on it. So just really diving into the jetting as everyone else is on tbi’s.
Put in the 5.5 slide recipe this morning. Test drove and it’s got more power for sure, better pull. Sounds good, pipe bang/decel surge is minimal but I do like to have an idle. My first impressions are that this is a very “hot” jetting, so hopefully it’s not too lean.
800’
60f-ish
5.5
42-75(2)
32.5(might try 35)
490(might try 500)
S-4
1.25 on air screw.
I’ll ride it later today, but it definitely feels better. The “might try” up on jetting is me not wanting to be too lean as I do go into upper rpm’s a lot.
On the needles, 42-75 vs 43-75, is 43-75 (2) just 1/2 clip richer than 42-75(2)? Are these needles that close?
Yes, exactly right. The 43-75 has the grooves cut 1/2 clip richer than 42-75. I think it’s a small but very beneficial difference on these bikes to make them perfect across wide temp spans.
I’d def try the richer pilot and main if I was you. You don’t want to be too close on the lean edge. Keep your ears open for any pinging.
This is why I settled on the 5.75 instead of the 5.5. The 5.5 seemed to be prone to a lhint of rich stumble that wanted a leaner pilot or needle than I wanted to do.
You also need to adjust your power valve as it does play into the jetting if you haven't done so.
Your 1 3/4 in from flush? Or completely out? 1 3/4 isn’t far from oem setting I think.
as fgr01 stated he went with 5.75 recipe for the richer setting…isn’t the 5.5 richer? Did you do the 500 and 43-75(2) with the 5.5?
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.
Pit Row
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.
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
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