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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.
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
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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.
Okay, I’ll just leave the slide alone. I see you recommend the 43-75 and 42-75 so don’t bother with the 42-74?
Also i can’t find a 510 main that is genuine. Any idea where to get one?
https://www.jetsrus.com/a_jets_by_carburetor_type/jets_mikuni_4-042_main_Hex.htm
Mikuni doesn't have them that size so aftermarket is your only option. I've ordered from here and have zero problems. Also you need to adjust your powervalve when you rejet as it does change things. On the small bore bikes we were starting at 2.25 turns in from all the way out and adjusting from there if needed.
Pit Row
I believe all the 510 I have are either ProX or EBC. They are also available on Rocky Mountain and other places in case you're already over there ordering needles, etc. Order a few sizes. I'd have 480-490-500-510-520-540 on hand if I was you. It will take a little tinkering to get it perfect and to adjust once humid summer comes.
On the needle, the 2022 crank recall and ECU issue ended up causing me to use the leaner xx-75 series needles. The xx-74 caused a rich bog when opening the throttle on the 2023 Gasggas 125 I jetted. Others have stated the same, that there was a bog or hesitation that was hard to get rid of with the xx-74 needle. My post is back on page 31.
Echo what AJ said on the PV. 2.25 in is a good starting point. Ultimately you need to get the jetting sorted first and then fine tune the PV to synch with the jetting.
Thanks guys. Awesome info from yall! I did see the pro x, ebc, and jetsrus options but didn’t know if they were true to size. Will get all those main sizes/ needles and report back after install.
Finally got the carb parts and went with the suggested setup. It runs great! Im very satisfied with how it runs. I appreciate the info and help from you guys!
Like i said, I don’t have a ton of knowledge on jetting. Just basic knowledge i guess to get something running decent. As far as the humid summer goes. Do you have any advice of which direction id be going from the recommended setup? Currently 50F and these settings work.
Needle- 43-75 Clip 2
Main- 510
Pilot- 32.5 (could use 30)
When it gets hot and humid you might start developing a rich hesitation as you roll on the throttle right at the transition to the taper of the needle. That will be your sign to go to the 42-75 clip 2.
If you have some time on your hands, experiment with larger mains. Try 520 and then 540. Just to know the effect. These bikes really like a big main. I am typically always running 540-560, but I only do MX tracks hard on the gas and I also run avgas.
I run the same jetting from 40°-105°F+. When it drops below 40° I need to go up one size on the pilot, down one clip on the needle and adjust the air screw.
Just an update as i finally have my 23 GG 125 sorted out. Brief history is i started with the stock Mikuni (and while i sometimes had it jetted pretty good) it would often need constant tweaking to keep correct. Sometimes i would get it running good and other times i would seem to go backwards. The jetting recommended here really helped but i feel my particular bike is on the worse end of sensativity if that makes sense. I literally tested a ton of needles/ clip positions / pilots & AS combinations....
Anyway, i ditched the MiK for a Keihin AG from TSP (with their jetting specs) out of frustration and it was much less sensative but still had the off idle / transition rich condition. I chased it with pilot jet / AS & clip changes but it was never totally clean. Dont get me wrong it was ridable on a track but it would begin to load up if riding slow like through the pits. Member FGR01 really helped me get this sorted out with the much leaner needle that i ended up with. Can't thank him enough as i wouldn't have gotten there by myself seeing how much leaner the straight section is from the OEM diameter.
Here are my final settings. 182m 48p N3CK 4th ~1.6 AS 50/50 110 sunoco/pump 93 40:1 Maxima K2 0-1000' elevation tested@ 40-65*F
Thats exactly what happened at camp coker and just put the 42 in and its fixed. Great advice and i appreciate it very much! For my reference is the 42 a leaner needle?
Glad that worked as intended. Yes, 42-75 has grooves that are cut 1/2 clip leaner than 43-75.
2021 tc125 vforce4r reeds FMF fatty and Powercore 2 silencer. I’m having a bog when I crack the throttle open.
#5 slide from jd jetting
S-4 needle jet,
42-75 second clip,
32.5 pilot
510 main
air screw 1.5 turn out.
Not sure about pv I have the tool ordered. I’m going to try a 35 pilot tomorrow.
What fuel are you using. Make sure you are mixing 40:1.
Make sure you swap the jet block gasket for the JD one and also make sure you verify the float height at 8-9mm.
After all that, put in the 42-74 needle on clip 2, 35 pilot, and 520 main... 540 if it's cooler and not too humid.
I am mixing 40:1. I have replaced the jet block gasket. I’ll have to order the 42-74.
Thank you for the help.
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