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sea level , 53°F
5 Slide without notch
500 MAIN , 35 PJ, AS 1.5 , needle 43-74 2 clip , PV 2 turns, , float height: 7-8mm , 40:1 motul 710
Im having a hesitation when im reaching 1/4 throttle, its more noticeable when im gentle with the throttle in 1st and 2nd gear. If im more agressive with the throttle , the hesitation goes away specially in 3rd, 4th gear. Today i put the 42-74 needle 2 clip, but i cannot test it until thursday. i didnt feel confortable using that (42-74) needle with this temps but my question is, when the temps reach 75-85°, (the time will tell) but maybe this rich hesitation comes back, is it safe to use the 42-75 needle? i see people using the -74 needle at 80°F with success and im using it at 53°F, that confuse me a little bit. lol
thanks guys
Correct on the air screw. Measured by turns out from full in. Make sure you are counting full turns and not half turns.
The hose in the center of the bowl is the bowl overflow. It leaks from there if the bowl is getting too full from either incorrect float height or the float needle sticking open. Take the carb off, bowl off and inspect the float and measure the float height. Should be 8-9mm. Test that the float needle is closing properly and replace as needed.
Yes, try a 35 pilot.
What are your temp and elevation (I assume hot, humid and sea level in Florida)? What gas, oil, and ratio are you running ?
Yeah you should have none of that hesitation. Put in the 42-74 on clip 2. And I also think you should be getting more towards a 520 or 540 main in those temps. On my 150 I am running a 540 even in crazy hot Arizona and elevation 400M. As a tuning option, yes you can try the -75 needles. I used them in some of the 2022 125's that were prone to a roll on rich hesitation. Don't be afraid to try them.
I actually moved back to Indiana! Okay great I have the air screw correct. I am at average 65-80F currently and 500-1100ft elevation. I am using Sunoco 110 with Amsoil Dominator mixed at 50-1. I know the float needle works freely, but I have not measured float height yet. I bet it is set too high. I will check it. Also, when do you really know when to adjust air screw? Is there a good way to test it back and forth to see where it really wants to be?
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I set the air screw by feel and ear. On my 150, I am either at 1.5 or 1.75. If that range is not enough, that is my indication to swap the pilot.
Update: now with 42-74 2 clip , is much better , im pretty happy how the bike is runnig, you can hear it from the video. Today i had a MX class, so i could test it. I notice after i let the engine idle for a few minutes, starts to sputters/ hesitate but after a few full throttle passes it clears and stays running beautiful. i will double check the float height it look like starts to load up on idle. Im with 35 PJ 1.75/2 turns AS and 1.75 PV (i dont know if less turns is more bottom or 2.5 turns from flush is more over rev) and today its more hot. aroung 65°F, here is almost spring . Cold morning 55°F and a few hours later , its like 68°F . Anyway, im pretty happy with the bike, i will check the float height but that needle is spot on !. Thanks @FGR01 , i will order 520 main and 43-75 needle for 85°F+ temps.
Good improvement. It sounds like there’s still a bit of initial hesitation. Try a 32.5 pilot sometime. Especially as it keeps getting warmer temperature.
What elevation are you riding? I've also got a 22' 150SX, just got a #5 slide. Was going to try 42-75 needle and see what happens although i am at 5k'+ elevation so I may need leaner settings. It had a Keihin on it before and ran great but now its up for sale but I need to get it running decent to sell lol.
Also I have a few JD needles laying around from carbs I bought in the past does anyone know if the JD red with 2 or 3 hash marks will work for this 150? Not sure how to tell which JD needles are for which bikes after the paperwork has been lost for years lol.
I'm at sea level so my settings probably aren't very helpful, 42-75 has been good but I may be a bit too lean
I ended up sticking with the settings I had as its been great since that day, but I found when testing the vented airbox cover that the bike ran worse, stuttered and was not running cleanly. But with the non vented cover it runs great, would this mean my settings are a bit too lean? The last I tested the vented cover was probably a bit over a month ago, and the weather has cooled down quite a bit now, typically between 55-65F. Should my settings be ok to run in this cooler weather or should I look at going richer? We only have a couple weeks of riding left here anyways, but the spring temperatures will be quite similar, and a bit colder when riding starts in April.
Better with non-vented suggests the settings are lean, but those settings aren't very lean for a 150. However, when temps start getting down below 55F I would consider a richer pilot and main, depending on what the bike feels like.
Just picked up a 2021 MC125. Bone stock and has a pretty good 1/4 throttle bog. I was ready to pull the trigger on the parts for the setup in the opening thread. JD is back ordered on the slide. I found several favorable reviews on the JD jet kit so I ordered that and a jet block gasket. I mainly want to get the bike somewhat dialed so my son can get some seat time on it in the remaining nice weather. I've seached and cant seem to find if anyone has run both the JD jet kit vs the jetting in this thread. Or if anyone has combined the JD needles with the other components. I guess I'm mainly wondering how the JD needles compare to the needle specified here.
I ran the JD kit when I first got the bike and it didn't help the issues I had, but the bike is a 250. The JD kit is a band aid for the real problem, the slide. No the needles don't work with the jetting in this thread. They are a custom taper to try and get around the rich slide.
If the stock jetting has the 42-71 needle, try putting the clip all the way at the top in slot-1. That usually minimizes that 1/4 throttle stumble fairly well until you can do the full setup from here.
Ill try that for this weekend. Do you find the recommended jetting in the manual to be close when utilizing stock carb components? We are coming off of MC85s and the recommended jetting was always a bit rich. I love the pwk carbs and am really tempted to swap this one over.
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.
Pit Row
What fuel, oil, and ratio are you running ? Everything else stock? Reeds, pipe, muffler, etc?
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.
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