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Thanks for the reply. I didn't find the JD kits to be any improvement on our 85s. Guess I should have gone with my gut and just waited for the slides to be back in stock. I'll definetly give them a try though now that I already bought it 😞
The manual for the 125 is not as useful as the 85 one. Basically because the 85 has the correct slide but the slide in the 125 is way too rich.
The easy way to decide between the jetting in this thread or a PWK - are you a tinkerer that doesn't mind fiddling to get it right or do you hate jetting and just want to drop something in and rip?
I fall into both categories. I don't mind tinkering to get things right but if I can find a setup that will allow the bike to run well and not have to constantly mess with it, I'm all for it. I have a lot of experience with Mikuni VMs on lots of different 2 strokes over the years. I have recently grown to love the PWKs because they work. I have a summer setup and a winter setup with just air screw adjustments for minor variances in temp or altitude. The tmx is foreign to me but I guess I'm willing to learn if it can be made to run well. My boy is coming off of a shoulder injury so last night was the first time he is able to ride it. It has stock jetting in it, 35 p 500m. It is absolutely horrible in our current temps. Lean on idle, rich everywhere else it seems.
What fuel, oil, and ratio are you running ? Everything else stock? Reeds, pipe, muffler, etc?
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Bike is stock, 35 hours. Think even the piston is original. C12 mixed with pump 91 50/50, 36:1 dominator. Same as we run in our 85 and supermini.
If you want to mess with the Mikuni, start here. I've always used 38:1 or 40:1. But 36:1 should be pretty close. If anything it will lean everything out just a hair.
Slide 5.0
Replace jet block gasket with JD
Set float at 8.5mm
Needle jet S-4
Needle 42-74 (Or possibly 43-74 as it gets cooler, I'd order both)
Clip-2
35 or 37.5 pilot
540 Main
If you want to jump right to a PWK, either pre-jetted from JD or this are good starting points. I prefer to use the 2016 reed block manifold with the PWK for proper fit but it is not absolutely necessary.
https://sbmotoperformance.com/product/keihin-38-air-stryker-short-body-…
The JD jet kit showed up early so I threw it in before heading out today. Night and day better than what came in the bike. The bike idles great and transitions well into the mid range.
The jetting that came in it was not what is listed in the manual. It had a 25 pilot, stock needle was in the P1 and a 480 main. Air screw only turned out a half a turn and it was still too lean. It seems someone had tried to address the issue before. Stock rubbery jet block gasket was in there and was deformed.
I ran the recommended JD specs (for aggressive riding) which was 32.5 pilot, blue needle in the p3 position and 460 main jet. Also replaced the oring and the jet block gasket from JD. Set the air screw to 1.75 out and bike ran pretty well. I do intend to try the jetting listed in this thread when the slides become available though. Thanks for the great info.
I threw a 6.0 in my 2022 150 but looking to test a richer one. Is a 5.5 enough of a difference to try or should i hold out for a 5.0? I have yet to find any 5.0's available.
I know there are guys running bigger than 5.0 and up to 6.0 with good success. But to me that seems like it would be way too lean for a fast MX rider and maybe usable for only tight woods riding or something like that. The 5.5 will definitely be a noticeable difference and you could minimize the leanness by doing the front slide notch. You might be kind of on your own to figure out the rest to go with it unless Digger has some ideas.
I've been using the setup (page 1) for the small bore with great results at sea level, from 45°F- 85°F with only air screw adjustment . Now at 85°F im starting to feel a little sputtering in the transition to the needle (1/4 throttle) again , but im gentle with the throttle, maybe with a more agressive ttype of riding , that sputtering goes away (clean) , i have in my hand the 43-75 needle, but i dont know if its gonna be too lean . I think im good with a little rich jetting. At 85° the AS is 2 turns 2.5 with 35 PJ, i will try 32.5 1.25 turns maybe that help with the transition. (Also im using E10 fuel that doesn help either)
Does anyone have any specs for a JD red needle on a 150sx at 4500' 65 degrees? I have the needle but no info on it lol.
...keep in mind with the JD needles that there is more than one "red needle". Same goes for the blue. If you look at the top of the needle under the clip positions, there are engraved marking rings that are identifier markings. For the longest time, I thought there was only 1 red and 1 blue needle. Turns out JD has multiple needles with different diameters/tapers. After talking with JD about this, he asked me to send in pictures of the needle to properly identify it. Get in touch with them and they will help you properly identify the needle.
@AJ565 @FGR01 @digger
I had dm'd Aj about this but wanted to ask others as well. I recently got a 2020 ktm 150sx. I have that annoying stutter in the mid range around a quarter throttle to like 1/3rd. It clears up in the powerband. The bike also loads up at slow speeds and after lugging it for a little while if you snap the throttle open it will not respond well and need to clear out first. Im running stock factory everything, so it has the #4 slide, 42-71 needle, 480 main 32.5 PJ. I ordered the jd jetting block gasket waiting for it. The thing is I live in canada and ride my bike anywhere from 36 degrees f to 90 degrees f on pump gas. I also sometimes do some trails and occasionally track. What jetting specs, needle ect would i need. I currently have 460 to 520 mains and 25 to 35 pilot jets. Also if I modify my slide myself to a #5 how can I do that if someone can link or quote the process as I would likely be doing it myself with a Dremel.
Thanks.
Here's a thread with some pics and info on enlarging the slide. There's also some good pics and info from Digger on the earlier pages of this thread. I'll add my #5 slide pic here also for reference. Basically, you need to enlarge the existing cutout until the top of the arch is 7.6mm up from a level surface. This should be about 1mm larger than the stock #4.
https://www.vitalmx.com/forums/tech-helprace-shop/4-0-5-0-mikuni-slide-ajdiggerfgr-thread-spill-over
I think you're good on the selection of pilots and mains you have. You'll want to verify that your 150 has the S-4 needle jet in it as I believe it should. Otherwise you'll have to get that. Get the 42-74 and 43-74 needles and you should be covered for fine tuning across your temp range.
You're not going to find one setting that is going to be perfect across that huge temp range. You'll need small tweaks. I'll assume you're near the low end of your range nowadays. So, try these settings to start
premix 40:1
Float - 8.5mm
Slide - 5
Needle jet - S4
Needle - 43-74 clip 2
Pilot - 35
Main 520
Thanks for the reply
Just to clear some things up:
In the pic you sent the slide on the left is a #4 and the left is a #5?
Also regards to grinding let me know if my understanding is correct, I make a mark 7.6mm from a flat surface onto the front face, I thrn grind the peak of the arch up to that point however do not take material off the sides of the arch. It is to be gently blended side to side and front to back.
Yes I have the s4 nozzle as well.
In regards to jetting, whats a good rule of thumb for changing jets with temp. Is it every 10 degrees Celsius go up a main and 15 degrees Celsius go up a pilot? Also is will likely only be using the jets i have unless i need to buy other sizes.
Thanks.
0-30celsius I had the MJ always same, rich enough
For spring and autumn one/two size bigger PJ and maybe one clip at the needle when it started to bog on throttle openings
The stock jetting on the 25 85’s is horrendous IMO. I went through hell for about 10hr correcting it. Turns out if it would have just been jetted like a 18-24, it would be fine.
1100’ 45-clip 2-145 seems to be our sweet spot stock. CR8EIX 91non oxy
*edit- I realized I was responding something that wasn’t asked, but if anyone else comes in with a new 85 dumping plugs, hope that helps
Just as a confirmation as I will be grinding my slide to a #5 from a #4 i do not grind the highlighted portion in the image below, I blend up to that portion correct? (The image used is from someone else in the thread and it looks like they actually did grind this part?)
Pit Row
Hey all, after grinding my slide to a #5 as per diggers pictures and help, I got my needles as well and ran the bike (2020 ktm 150sx). I ran it with:
520 main
35 PJ
43-74 needle clip 2
#5 slide (ground 1mm from #4)
Outside temp: -4° C (25° F)
The bike started first kick and idled fine. However after it warmed up for a few seconds I began to put it around for 30 seconds to heat it up. I then tried to clear it out by giving it full throttle in first but the bike would not clear up no matter what. Kept trying to clear it and then it bogged down almost like it ran out of fuel and shut off. Wouldn't start after that, choke on or choke off. Any reason as to why?
Probably fouled the plug. Things get real weird below freezing. It's hard to get the bike up to full operating temp. Pull the plug and see if it's wet and black.
I honestly figured. Before I made all the carb changes, in its stock form it was doing the same thing in the very cold temps but I brushed it off as poor jetting for the weather. I just ordered a new plug. Ill update once I install it.
On a side note, how do these settings look as a starting point, I know im running the bike in colder temps than most people in the thread just because I wanted to test it, no real riding done below freezing. But thats why im running a rich main, pilot and needle.
First test with new plug, ran up and down the street. Doesn't die anymore runs. However at a low rpm if I pin it it bogs down signature lean bog, this is like fro near idle and and putting it around i first then pin it bogs. Would this be air screw adjustment, needle, or incorrectly ground slide. Jetting is as per above. Also still have a tiny bit of that sputter.
This is the part where jetting over the internet gets hard, lol. I have never ridden my 150 in temps that low. So, I'd only be doing best guestimate on what you should change. It does sound like classic lean pilot bog. There's one surefire way to find out. Put the next size up pilot in.
Got it, thanks for all the help. I don't plan on getting it absolutely dialed in for the winter as I don't do much winter riding but I'll play with Airscrew/PJ. excited for riding season however. guess I get a little eager haha.
Just some casual imput coming from someone who spent a lot of time jetting my 125 in colder winter conditions. As FGR noted an increase in pilot jet is the easy answer to try but i often found in really cold air < 35* that i needed to do both a pilot and clip (try a half clip first) Easy way is get some needle clip spacers so you dont have to buy a million needles while testing. https://www.goodwinperformance.com/product/520-shim-kit/ You can stack these to .5mm which is a half a clip.
Also you should be running the radiator block off per the manual so the motor is at the correct operating temp or all your testing is on a cold motor.
gluck
I have 2020 150sx also, when temps are close to 40 F (sea level) in the morning i have to set the airscrew like 3/4 turn out to make it start and when temps are a little higher in the midday, 1 , 1.25 turn out is sweet spot . So i’d try 37.5 PJ at those temps and avoid to let it idle for too long thats when loads up. Once its warm, try to clear it out in 2nd , 3rd gear
I have a 2019 YZ144 with the Mikuni that I’ve done a lot of testing on for strictly riding moto, track is at about 400 ft and in South Texas. I know the mikuni’s between the YZ and SX are different but trying my jetting may help you with your Mikuni. My bike has an Athena 144, VForce 4, vortex ECU
Jetting:
Main: 460
Pilot: 40 (any leaner and I feel like it it gives up some power down low but it does have a cleaner idle but I have my bike set up not to idle for best throttle response)
Slide: 4 cut to a 5.0
Jet needle: I’ve tried the S1, S4, s7, and S9 (kx125) currently running the S7 from the S4 and I’m really liking the midrange power from the S7.
Needle: I have a ton of different needles that I’ve tried, I have a standard needle from the 04 Kx125 6chj that I put in with the s9 nozzle and it rips but would have to really clear it out.
Current set up is 42-74 clip 3 with the s7 and it’s pulls hard and has no hiccups, or hesisitation, no lean pops, or bog from 1/4-half throttle.
Needles I haven’t tried with the S7 yet that I have are 43-74, 44-74, 42-75, 43-75, 24-74
A/S: 2-2.5 turns out
I keep tabs on this thread as I may pick up a carbed 125SX in the future….but reading through makes me really appreciate my FI 300SX”s..😂…..
The 460 main is way too lean on a KTM125. Those bikes like the fuel.
Better hurry up. Not going to be able to find many decent low hour ones for long. I know people like the TBI 300's, but the TBI 125's are absolute dog poop compared to the carb bikes.
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