Jetting the 2021 KTM 125XC with the Mikuni TMX38 Carburetor

[@kenkammerer6720]

My first experience with the TMX38x was on a 2003 KX125. Converting from Motocross to woods weapon riding in the mid-west. Needle design had me approach this from a different direction. Once the pilot was dialed in, I went from the stock 5.75 slide to the 6.0 (option through Kaw parts). Two turns out from seated on the air screw. Clip, second position from top on the needle. Down 2 sizes on the main. Really a responsive carb when it came to the air screw.

[@highlandcycles]

Right on.

[@LORENZindustries]

Sweet rev tune to “warm it up”. The whole point of warming it up is to not goose it and drive a cold cylinder into a warm piston.

[@ericxnelson]

picked up a used 22 125xc today and it's got the sputter. Gonna give this a go and get those vent hoses rerouted in the process. Bike has 20 hours on it, like new!

[@highlandcycles]

Sweet

[@chriswest9641]

Thanks man. Your vids have saved me. Issues with 2020 yz125. Was great, then went to shit. JD kit just showed up in the mail!

[@marticusthegreat3633]

I’m having the same problem with my 21 yz125 and just ordered a jd jetting kit.

[@250race]

I like the tapper needles I run the 6chy12-82 or the -83

[@orijinalgamesta9738]

Bro!! Ive never seen anyone route the carb lines like that or even heard of it. Brilliant! i have trouble with my bike dying when i get in deep water and i bet you just gave me the fix. 2017 250 XC (CRB) lol. CRB is for all the TPI guys who have to state year, make, model, engine size and then tpi whenever they talk about their bike. It's even more hilarious when they try to say it real fast.

[@highlandcycles]

Hahahahah. That’s funny about the CRB. Yeah the vent line deal will solve your problem.

[@motofam7265]

Solid video man! I actually just did the jd kit on my 21 tc125 last night. Bike had maybe 3.5hrs on it. Float jet gasket was completely warped and not sealing. Keep up the good vids

[@highlandcycles]

Thanks. Yeah, it’s weird how bad they are

[@devonrose888]

Sounds good but you forgot to check the float height. Crucial on the mikunis because some come off from the factory.

[@highlandcycles]

I did. I just forgot to run the camera. It was off

[@youtubeaccount9058]

My '18 300XC with the Mikuni really ran like crap until I did the jet block gasket, and it was obviously blown. You hear about this things... it's real.

[@highlandcycles]

Yep

[@johnfavre1987]

Did the same with my 300 XC-W, always ran great and never felt the need for a carb change. Tucked the ends of the breather hoses inside the upper frame. Printed my own filter support. Still not sold on the TPI.

[@highlandcycles]

Me neither. I love my 18 300 with a carb

[@kentkeele7051]

You don’t have to do all that to re Jet just listen the hose clamps and rotate the carb. Nice to see it this way for the video tho. I can re jet in a couple of minutes.

[@highlandcycles]

Yeah, for a quick re jet I just spin it but it’s nice for people to see

[@myricastillo5097]

I’m happy you got a carb 2021 ktm 125 😄👌 I hear it’s very very rare to get one with a carb since they are going more to tpi .

[@highlandcycles]

Yeah. More and more are going tpi

[@WujoCaZa]

Great bike! But I didn’t suspect that gonna have so much gunk and dirt in carb from factory! It was o Austria dirt! Maybe in the front forks you would go with ohlins cartridges? You could make good video showing how to assemble it? 🤔 Regards from Poland! 🇵🇱

[@highlandcycles]

I think when I do the suspension I’ll be doing the KYB conversion.

[@scottphillips6560]

Hey thanks for the tutorial!

[@highlandcycles]

Awesome

[@puch7261]

what year tmx38 carb you use on the ktm?

[@highlandcycles]

The mikuni came on the bike

[@200xcBruce]

Surprised you did not check float height

[@highlandcycles]

I did but didn't film it. It was off a little. I have that covered in my in depth Mikuni video

[@raulogarci]

hello good video !! With the jd kit it is possible to remove the hated pipe bang ??? greetings from Spain

[@highlandcycles]

Yeah. Just have to get the jetting right.

[@bloomerb4162]

I have a 2022 tc 250 i bought used 3hrs. First few laps it ran great, then it started lean bogging high rpm and when letting off back on throttle quickly. You think it's just got some dirt or gunk in the jets? That's not a symptom of bad block gasket is it.

[@highlandcycles]

Probably clogged but I’d do the jet block gasket anyway

[@bloomerb4162]

@@highlandcycles yeah I went ahead and ordered the gasket.

[@burstcasino]

My '22 Beta 300rr (which I know is not for you) already has the middle grommet piece on the Twin Air filter... What is KTM thinking on such a critical part... Heck my filter looks identical except for the middle grommet...

[@highlandcycles]

I have no idea. It’s ridiculous

[@user-wk9bu6xm7y]

What’s the best setting for the idle mixture screw not idle speed

[@highlandcycles]

Start at 1 turn out and tune for best response

[@richardhartley7094]

Sounds sweet 👍

[@highlandcycles]

Thanks.

[@brodyspencer]

I've heard you say be careful when removing float bowl screws and I tried but I started to strip out 2 of them👎🏼 what do you recommend I do to get those out? Excited to watch the 125 stuff. I love mine 🤘🏼

[@highlandcycles]

When they are tough I use a hand impact driver. I have some videos of me using one somewhere

[@KyleManley-b4n]

I use a small pair of vice grips Works every time!!

[@legowolf22]

Is that the same waterproof motorex you used on the swing arm bearings?

[@highlandcycles]

Yep.

[@freetaylor72]

man i got a jd kit in my 2023 beta, and now im trying to figure out how the needle clip changes every other circuit in the carb, the temps are colder and now my bike is running like crap. ive played with the air screw but it still seems like its lean. they gave me a 38 pilot and several mains and the chart says richer to leaner with the clip positions, and needles. how does changing needle clip position change everthing?

[@highlandcycles]

Every circuit in a carb effects and is affected by every other circuit. They just have more influence over certain throttle openings. The needle position is connected strongly with main jet size because it is metering the main.

[@kjw3823]

I realize this video is a year old but I hope someone can help me out with this question anyway. I just got a jdjetting kit for a 2022 Ktm 125 sx. In the tables for pilot, needle, and main jet recommendation the main jet recommended for the 125 is in most cases a size larger than what is recommended for the 150. That seems backwards as I would think that a 150 would require more fuel than a 125 and therefore need a larger not smaller main jet?

[@highlandcycles]

It’s a bit backwards of what you think. The bigger the bore, the stronger the pull on the carb. When it pulls harder you have to put a smaller jet in to keep the fuel to air ratio the same. The opposite is true too. Smaller bore draws less so a bigger jet is needed.

[@kjw3823]

@@highlandcycles Appreciate the response.

[@candrive4916]

If you use the red needle in a pack you don’t fancy selling me a blue one do you ? 🙏

[@highlandcycles]

No. I hang onto them for when we go to sea level

[@legowolf22]

They added the blue cause they know Yami's are better....😂

[@highlandcycles]

Exactly

[@kyledudek9336]

If you snap the throttle open from a low idle does it bog then rev out?

[@highlandcycles]

No, It just revs instantly

[@kyledudek9336]

@@highlandcycles that’s the issue I’m having with my 2022 ktm 125, I just did the jd jetting kit and the gasket I’m not sure that it got rid of the problem though. Any ideas on what could help?

[@paulb7773]

@@kyledudek9336 you need a bigger pilot jet

[@painsrides]

"Let's make Carburetors Great Again"........ wait 👀

[@highlandcycles]

Hahaha. Yes

[@harro9447]

Hell yeah 🤤

[@DezertSlayer]

Fun 25!!!

[@highlandcycles]

The Juan Deuce Nickle!

[@robmccauley1073]

Crazy to have to tare it down that far just to jet it...... Must be a KTM. LOL

[@highlandcycles]

🤣😂

[@tc1254]

So the issue I have with my 18 125 is that I have a 30 pilot and 480 main 40:1 knotched slide, when I want to be in low rpm like putting around hopping over small logs for let’s say 10/20 minutes and then I take off it acts like it’s about to kill the plug and no I don’t mean to clear it out it’s killed multiple plugs this way, I have it jetted lean to counteract the issue but it still does it, what should I do jet block gasket? It idle and runs crisp all throughout the rpm range just not when I’m 0 to 1/8th throttle

[@highlandcycles]

I would look at the jet block gasket for sure. Also, I had my main down to 430 to get it super clean. That’s at 6000 ft though. After putting the RK head on, it made everything much better

[@tc1254]

@@highlandcycles I’m close to sea level and the way I have it jetted it doesn’t splooge once warmed up it barely smokes like I’m talking about tpi smoke level , I was thinking about the rk tech insert I guess after I do the jet block gasket I’ll try a head insert

[@highlandcycles]

@@tc1254 yeah. I would get the jet block done and then do the insert. It’s a massive upgrade no matter what. Make sure you let them know you talked to us about it. I want them to know that I really appreciate their help.

[@tannerciano3535]

Just got a 2021 KTM 125 XC and has about 11 hours on it but whenever I open throttle to fast it’ll bog out, any suggestions?

[@highlandcycles]

Gotta get the jetting right. Not sure what elevation you live at but we are at 6K. I also now have an RK TEK head on it and it really rips.

[@tannerciano3535]

@@highlandcycles I’m in a very low altitude, around 60-100. I’m just trying to get my carb off and make sure everything in clean and put in a smaller main jet and see if their is a difference. Thanks for responding!

[@sptnk87]

@@tannerciano3535 how did it go?

[@garrettanderson7803]

I wish they would get away from the phillips screws.

[@highlandcycles]

No kidding

[@stevemx2778]

I think you go on wrong way Better set float height 8,5, 42-74 needle 2 or 3 clip, idling jet 32,5 main 490

[@michaelbarnato4220]

like Yama betterWay less work to work on carburetor

[@highlandcycles]

Agree about the carb. But this thing is pretty sweet.

[@robhayter484]

How many turns out on the air screw was you in the end ?

[@highlandcycles]

2

[@robhayter484]

@@highlandcycles do you know how many turns out these should be from stock

[@robhayter484]

Coz mine came stock at 1 turn out ,I’m now running the jd blue needle but I’m not sure how many turns out I should be now

[@highlandcycles]

@@robhayter484 every bike and every environment is different. Tune it til the bike is running right