How to Tune/Adjust KTM 2 Stroke Carburetors
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- Опубліковано 9 лют 2025
- In this video, Jeff Slavens, with www.slavensrac... demonstrates and explains the KTM 2 stroke carburetor pilot circuit. This video will take the user through the process of checking your 2010 KTM 300 Carburetor and all two-stroke carburetors for optimal use. KTM carburetor parts need to be tested, prior to use, especially during the changing seasons. Jeff will explain and demonstrate the process of testing your KTM carburetor to ensure that it is ready for riding use. In this video, Jeff gives all the clues and methods for testing the pilot circuitry through the KTM carburetor. Shop and find all the KTM carburetor parts your bike may need at slavensracing..... Or call Jeff & his experienced team today for further information and details on dirt bike parts and products - (719) 475-2624.
2016 KTM 300XC. Bike was dying on the downhills when clutch was engaged causing rear tire to lock up. Went to a 38 pilot jet and followed your tuning procedure. It's like a whole new bike. The chart in the manual was right, but you were more right. Thank you!
You're welcome.
Once in awhile I like to watch Jeff's tutorials. I seem to forget a lot of stuff and ones like this are good reminders unless you didn't already know this stuff.
I was thinking that he looked like Heisenberg (Walter Whyte) before I see the comments but looks like everyone else did too. Anyway great explanation and demo it was crystal clear, great vid man
Thanks for that ,just got an Suzuki rg125 f ..and that's exactly the problem...and it wasnt change in temp or season ,just previous owner messed around with settings , after rebuild .. Big thank from Ireland..!!
Cheers Jeff your videos have been amazingly informative and easy to watch! Really like your rebuild videos too!
Thank you for this excellent explanation of the pilot
circuit! I end up with a bunch of goo coming out of my pipe. After I follow
your direction, I hope the goo will reduce substantially. Otherwise I need to experiment the needle and or a smaller main jet.
Sheesh, take it easy. Where did I say you suggested a different fuel/oil ratio? I will watch the video again for sure. Thanks for the help and great vids.
Thanks for the easy to follow explanation 👍
Glad it was helpful!
hey I already know my way about the carb on my ktm sx 250 but this was really helpful,wish I had found this ages ago when my bike would not stop fouling thanks for the info great vid!
Hey my I’m from Australia, my bike fouls a plus every ride where should I start
Jeff, I purchased a used 2011 300 wcw at the beginning of may but have only ridden it a few times. I was riding it today and it would stall as the rpms approached idle. If I catch it and open the throttle quickly enough it won't die but I can sense a slight bog, if it dies it won't start back up unless I let it sit a few minutes. I didn't have this problem until today. The only difference is that it is a little warmer now (central Texas). It has the same gas in it that was in it when I bought it (about a month ago). Thanks
Jeff, thank u very much! For making me understand what shall i do with my bike! In all ways of tuning! A lot!
I think you're right. I lowered my fuel/oil ratio from 40 to 32:1 and it runs better now. Those 150s are jetted super rich from the factory. I also had to let the air screw out a full turn to clean up the mid range fluttering.
I wished i'd saw this video when i had my cr125, this is exactly what it was doing. it had bit of a bog to it at lower rpms once it got to the other gears and jets at more throttle it opened up. Now have a KTM 250 exc which is tuned perfect for now untill summer then i may have to come back to this video great tips!
Just messaged you earlier about leak testing a 2 stroke , and I just installed v force 4 reeds and cage it leaks with or without the gasket between the boot are there any fixes besides rtv sealant ? And why would this be on a new v force cage
Thanks Jeff, this was very helpful!
Thanks for posting this! I have an 97 lt250r with alot of problems!But now I know this is not one of them!
I live in Loveland and ride in the Denver area. I have a 03 cr250 that I can't seem to get to run right. Motor is all stock with a FMF pipe, silencer and a twin air air filter. Stock the main jet was a 420. I'm all the way down to a 350 and it still won't wined out.
I have a ktm 125 sx, just had new top end, new plug and air filter.
Bike ideals fine runs well in first gear but bogs in 2nd gear but fine when I manage to get it into 3rd any suggestions? Cheers
How would the needle position play affect with the bog? Mine hardly bogs under a blip but a little more under a load at lower rpms. Never box through the rest of the rpms.
Do you have a video dealing with main jet and needle settings? This was very informative.
@4NICKW high rev can also be caused by the carburetor. A faulty throttle cable for example. If it is binding up inside the plastic tubing, it could prevent the throttle from returning to idle position. Also, the return spring could be bad. On my 1995 ktm 250 exc, I had a similar issue. I had to popstart the bike (long story). one time when I started it, it took off, high rpm. i pulled the clutch in and it continued to scream. after inspection, return spring was the issue.
Morning Sir
Is the only indication of correct adjustment? When the bog is out with quick throttle response? When I’ve played with Air Screw, turned in and slowly turn out, it kinda blubbers/struggles to seemingly idle. Then backing out and idle climbs /smooths out. Turning past that point seems to make it worse.
Was that the best adjustment for that temp & elevation?
And of course check for Bogging.
Or is bogging the only indicator needed?
My ole KDX thanks you
Greg
yeah, there maybe a window with an oil fill level line too. having to hold the choke does confirm your either getting oil in your fuel or an air leak, if theres no oil missing try find that air leak.
Great video :) I liked the explanation about the cold dense air effecting the jetting because my bike has recently started bogging really bad and the temperature has just gone down a lot outside. My plan of action is to first strip the carb, make sure the pilot jet is clean, new spark plug and then adjust the pilot air screw. Does this sound about right?
i just drank a bottle of ed wine and four bees and i kow Jeff Slavens knows his stuff
+dave davo Ethylic illumination... :)
Are you coming to Tough Like RORR this year?
I'm old. No more racing for me.
Great video I wanted to know if you could help me I have a problem with my 2000 kx250 carb. If the jet to big can it make it run out the bottom over flo? It only dose it when it idling. It almost like the needle getting stuck open, but I check it and clean it check the float its good everything good on it, Ive run out of ideas. But I think the guy I got the bike off of got the jets to big in it to. So what you think?
The jets have nothing to do with overflow, the floatvave is worn, or float level too high,
or the float aint floating,= holed,
blackie1850 Ok thank you that helps a lot! Thanks!
Could he drop the needle one clip position? BTW , can you do an in depth video on why KTM forks are so harsh? I have a 2010 250sx and I'm curious as to what you do to diagnose such issues.....
Revving on its own sounds like an air leak after your carb, but blue smoke could be oil getting through a crank seal. It'll run, but erratically. Have you checked your oil level.
Helpful vdo, thx. My 2strike scooter seems to bog in midrange when the weather gets cold. A few months ago, I put an aftermkt, less restrictive exhaust pipe on it, so I think if might be running too lean as the weather gets cold. Just as Jeff describes in this vdo. I will try adjusting the pilot jet per your instrux to see if that helps. Gracias!
The Needle controls the midrange..... Try raising the needle one notch...
Would this apply if you have a quarter turn throttle or more aggressive throttle cam?
Yes
32:1 is the recomended ratio for mx bikes of all sizes... the air screw will effect the mid range but its not the best idea to mess with because it can cause your motor to blow if you lean it out too much.
Jeff I have the 2019 KTM 300 XC. On the Carb its a TMX 38 Mikuni Carb. Do you know what the Factory Turns on the IDLE Screw is? I took the Mjet out a factory 450 and put in the 440 Mjet. I turned the Air Mixture screw to the 2.5 turns for the 440.
I touched the Idle screw by accident... I was not suppose to tough this screw set by Factory. I have always been curious what or how many turns was it. I don't know. Right now I have it set at 5 full turns out from the beginning.
another great video, keep it going.
Dude,
Thank you for sharing your knowledge. I have a 2001 KTM 300 that is not making the power it should be and stumbling/missing at low to mid range rpm. Going to pull the carb, clean, and inspect first off. Also going to check the baffling in the exhaust. Almost new cylinder/piston re-plated by Millinium. New crank case seals. Any other ideas ? I will take look at the power valve also.
Check for vacuum leaks too.
"Blow it out real well" only us slow 2 stroke riders will understand. 😂
Great video Jeff
can you do a vid on how to check/replace the jets etc?
hi jeff, big fan i watch all your 2 - stroke videos, thank you very much by the way you've helped me a lot and you don´t know it!. i have a question regarding the carb tuning. i actually own a ktm exc 300 2010 with 100hrs on it. when its hot and i've been running for a while, when i rev it hard it stalls a littlebit just before reaching top rev, it does it in neutral or running on any gear, when you rev really high it stalls a little bit... is it the carb? or she asking for power valve rebuild?
Mountain hardware FTW! (i love alpine climbing professionally)
What?
I recognise that carb from my old 2001 yz 250. Thanks for the info!
Tanks for the answer. yes ive used 110 becouse i was having problems with the muffler tip and the reed valves. now i have all isues repaired and i use 130 main jet that was in the carborator when i buy it, and the pilot jet is a 50. what set tuning to my carborator do you recomend to my mhr team2 fully tuned ported ? 150 main jet and the pilot jet ?
Great video! Very helpful. Thanks!
Hello Jeff, I have a ktm 125 exc and i am looking on internet for little improves that I can do on my bike to improve the performance, do you know more modifications that I can do without spendig much money ?
Thank you for your help!
OK, so My 08 200xc runs great all the way through the throttle range, but at 3/4 to full throttle it is really flat. full throttle feels no difference then 3/4 throttle. So is it lean on the main? Jd jet kit, blue needle 3rd clip and a 175 main. 800ft elev. Thanks for the videos!
ive just had a rebuild and ive had the bike back road it about three times went to start it this morning its been left out in the cold all week scince saturday and i got it warm pull the throttle back and its started to bogg not took the carb apart but can some 1 help its so close to christmas and shops are now shut
@slaverace1
Jeff do you have some videos about basic carburetor setup? I bought my bike used and the jetting was all wrong, the pilot screw and the air screw were both turned all the way in and the bike ran too rich, spewing oil out of the tailpipe regardless of the fuel:oil ratio (tried up to 60:1). Im planning on taking the whole carb apart and starting over, using your mountain jet kit (I also ride in Colorado). Any help or links would be greatly appreciated!
Hi, I'm from Argentina. Have a 2022 300.. first 2 stroke. After 4 hs since brand new it started making PIPE BANGING, QUITE LOUD. Is it the jetting? I'm running stock jetting, bought 2 suzuki needles but have no idea honestly, this is my first 2 stroke
Hello, 2020 models are fuel injected, not carbureted. You will need a different ECU to resolve that issue and gain horsepower.
slavensracing.com/shop/ez-ecu-for-ktm-hqv-gas-gas-300-tpi-by-coober/
slavensracing.com/shop/slavens-mule-get-ecu-race-kit-for-ktm-hqv-250-300tpi/
@@slaverace1 but my beta 300 2022 is 2 Stroke sir and its carburated
@@slaverace1 my mistake was that I didn't put I have a beta.. I'm sorry for that sir
@@andresbossus927
Sorry, since the video is titled KTM I assumed you had a KTM. A JD jet kit slavensracing.com/shop/jet-kit-beta-jd-jetting/ will help or a Lectron Billetron slavensracing.com/shop/billetron-38mm-2-stroke-carburetors-by-lectron/ will fix it and improve performance.
Hi,
My NSR150 has a few carb issues i think. I'd like your comments. It is hard to start in the mornings, but once warmed it starts first time. In the mornings it idles at around 2000RPM and then once warmed up, the RPMs increase to around 3200 if im in gear and the clutch is pulled in or i slip it into neutral. It doesnt happen all the time, but mostly happens when the engine is warmed. Also... pulling my front brake brings down the RPM slightly? Any advice?
PS.. awesome vid :)
My 2011 KTM 150XC misses at the top of the rev range. Sounds like a gentle rev limiter. Is there any sort of rev limiter on this bike, or do I have a clogged main jet or something?
love youtube always learning something new :)
The added compression may make it leaner.
This is exactly what my son's KTM SX 50 is doing. So it will bog sometimes and sometimes I hit the revs and it takes a few seconds to come back down.
It's advisable to screw that brass screw all the way in then back out 2 and a half turns?
Many thanks
No, set it so that it has good throttle response and idles correctly.
Jeff Slavens I've played with it and can't seem to get it right. Doesn't matter what I do. The KTM manual isn't very clear either. Thanks.
go up 1 pilot jet size and start with air screw 2 turns out
will a larger main and pilot do the trick or will you need to adjust the clip position? becuase i hate moving that damn clip
I have a 180 main jet and a 42 pilot jet the pin is set at the second notch it will jut rev on its own and blue smoke comes out of the exhaust smells like mixed gas also
just to make sure im right, if its lean/boggy from idle with the air screw turned in over 2 turns out you need to go smaller with the pilot?
what do i do if the bike is doing full throttle when it is on idle? btw great vid!
Ajust the idle screw
wheelie!
could also be an air leak. Spray starter fluid around the air boots that connect to the carb.
I had the same problem with my ktm 125 exc, i need to ride with a 190 main jet, is it normal? A ktm 125 are supposed to have 168-172.
do you have any table for alttitude, temp, for where i can start with my jets? also what needle recomends for the 300 ecx
Kind Regards
+Rodolfo Morales
Sorry, no charts.
+Rodolfo Morales still looking? Owners manual has those charts. www.ktm.com/us/service/manuals/
Just find your bike , carburetor page of manual, and find the right chart for your bike.
this guy looks like the walter white for offroad biking
+Hendrik Le Roux Heisenberg!!!! lol
And sounds like Lebowski.
"it's time to cook the pipe Jesse"
Hvguy 😂😂👌🏻
Hey Jeff question my bike does the exactly same thing but does not bogg at all when I ride just when its idle can this be a big issue in the long run?
Any bog indicates a lean condition that can be harmful.
Hey I have a 2001 cr 125r and I just recently changer my 370 main jet too a 340 and it runns so much better it doesnot bogg or anything what else do I need to change in the carb and is it bad too run a 340 Cuzz I saw this article that sated my bike lover too run a 340
I am having a very similar issue with my 99 300 exc. It bogs/sputters when it is supposed to reach the power valve. I am thinking to change the piston rings. Maybe it is not holding compression at high RPMs???
Hi Jeff just watched your video on pilot jetting and wanted to ask a question, I have a 2018 husqvarna te300 and installed a jd jett kit per instructions, well I’m still having a little bog off idle so I started to adjust the air screw and seemed to run a lot better but seems like my idle takes awhile to come down, it is still cold here in the north east but any suggestions? Thanks,jim
Cold air is denser than hot air and that makes the jetting leaner. A bog is lean and a slow return to idle indicates lean so richen it on the pilot or pilot air screw.
Thanks for the reply, to richen it up when the weather is cold turn the air screw in and warmer temps lean it out turn the air screw out correct?
yes
Hi i have a tuned scooter 2 t malossi MHR TEAM 2 tuned ported and i have a carborator 28mm oko like keihein a xeap copy. My question is when i start the bike she is fine and when i acelerate it does soun like your in the video she goes boooar and then acelerate more and shes good again.i use pilot jet 48 main jet 110 iddle all down and at lower rpms i cant run smoothe she starts to do that thing again booar boooar and when i acelerate at max she goes fine.i have it lean?and i have 3 quarters out
Helpful information thanks
Great video, thanks!
So 2-stroke carbs fuel/air screw is opposite of a 4-stoke right?
2-stroke: Turn in = richer
4-stroke: Turn out = richer
I have a yamaha dt 125 and the air screw is wound all the way in so far that its stuck and you can see were someone has tired to undo it and just messed up the head on it , any help on how to get it out ? and my bike does not idol at all ! when it gets to the lower revs it will just die or when i open the throttle it will sound boggy and just die after that could the air screw being wound all the way in be the problem for this ? and if so how far out should the screw be ?
I havd a 1999 ktm mxc200. its hard to start. (takes about 15-20 kicks). and once it starts it starts revving really high. I Just replaced the rings to help with compression. Should that totally fix my starting problems? and is the high revving just from me flooding it? or is the carb needing to be adjusted?
Hey jeff can I pick your brain for a second?
I have a KTM200 EXC (2012)
The previous owner has a pilot of 38, main of 158 and stock needle NOZI. I get a fair bit of spooge on the plug and exhaust. When I start the bike cold it does exactly as your bike did there, bogs down. But when hot, after some hills etc, it just dies at idle all the time, really annoying half way up hills after kick starting it if I fall off. Just seems weird to get all that spooge but be running such a lean pilot circuit? Can you advise/help??
Hello
i have a problem with my cr 250. it was going to extremely high revs as soon as i started it. so pulled it off the bike. cleaned it. made sure all the floats at working and the slide wasnt stuck. put back on the bike. made sure again that the slide was closed. started up and did it again. bike revs almost the red line. im sure if i loaded the engine it wouldnt be at full throttle. i can hear the slide closing still. could it be a choke problem? have you ever had this happen?
if i put a bigger pilot jet in will it make my bike idol better now i have a 50 pilot is calls for a 52 pilot jet but i don't know to change it or not???
im trying to put together a double barrel carbie for my rmz 450
can u post a video on 4 stroke perferably a ktm
saw the cat gave immediate thumbs up
I have a 95 KTM 300mxc and the top end is rebuilt but when I start it up it will idle fine bit when I ride it it will rev on its own like it stuck open one time when I continued to ride it not much to where it would kick up just enough to notice?
So turning in that screw will richen the mixture?
Turning the air screw clockwise cuts off the air and creates a richer mixture.
hii looks like stupid question but can someone please tell me where to connect those 4 transparent pipe I am really new on it watched some video and googled but I couldn't find diagrams explanation etc even no any video how to fix that. your support really appreciate. thanks in advance.
Haldun Yagci they are vacuum/vent lines just tuck them under the carb
could you help me please i have a 97 kx 250 she idles fine and runs good at low rpm then when i whack it open she starts to bog as if its running out of fuel and as soon a i back off she runs fine again. do you know whats causing this, thanks
what jetting changes should i expect when moving to a sx cylinder head on a 250xcw
i cant get my bike to idol what so ever. i can manually idol it with the throttle but thats it. ive played around with everything on my carb. any ideas?
i have an important question. i have a suzuki rm85 2 stroke and when i put a new spark plug in and i will ride for about 2 house and then it will die. i am fouling my plug after 2 hours of riding. can you help me so that my bike quits fouling plugs. and i never let my bike ilde. so i think it is runing to rich. can you tell me which way to turn the screw and which screw to turn. thanks you
how do i keep my plugs from fouling.. right now its 6 turns to the left?out so im guessing i nedd to go like 2 or 3 numbers smaller?
like 1.5 lol!
Yes and now I have to hold the choke for it to keep running and when I do it maxes out on rpms
I did NOT suggest going to 32:1. FYI: The air screw does NOT effect the mid-range. Try watching my video again, or maybe 10 times.
hey, i have a 1996 yz125 and i have some issues with it. i can go through around 4 hours of ride time before it fouls the plug. it also smokes a lot when its cold, but goes away when its warm. i know its not the type of plug i use. i run 44:1 premix with yamalube 2r. it has been rebuilt recently, and has had the crankshaft seals replaced recently aswell. i have the pilot air screw 1 1/2 turns outwards from seating, which is the factory setting. also it doesnt idle. any solutions on whats wrong?
how many turns out should a ktm sx 150 pilot adjustment be
+Blenzington
That is covered in the video.
is it 2
Hey how do i adjust the air on the dirt bike it only accelerates when i cover the fitlter almost completley so if i leve it like that its turns off on me so what do i do?
What i would say it has is that to much air on air fuel mixture rhats the problem what do i do?
jose castorena unappropriate air filter ,you might wanna change it or stuff it with some sponge or some thing like that!
WALID BETTAHI hey I tride that but didnt work I also cleaned the carb and mi pocket bike isnt working right I need to take the filter off and then I also have to close the end with my finger tips till I fill its starti g to accelerate othwr wise it turns off on me
did you try to fill the filter witha spong?
Thanks i did that a few days ago and it was loose but still it will bog down on me +brapinblarms1
Sorry, I don't have any other carb vids. I'll put it on my list.
hi jeff could you help me i have a brand new 2013 husaberg te 125 problem is if i try and take off at speed by giving it full throttle and dropping the cluch it just bogs for about 50 yards then cuts out, the dealer has tryed a few different jets but cant get rid of the problem, this is my second new 125 and last years 125 would pull in 3rd gear from a stand still
asi que ese es el secreto de ese vendito KEHIN, ACA CON EL CALOR QUE HACE EN ARGENTINA UNOS 35º EN ADELANTE LLEVO EN MI YZ 250 CHICLE DE BAJA 52 Y CHICLE DE ALTA 165 CON UNA VUELTA DE AIRE Y AGUJA EN 2 POSICIÒN
thanks Jeff!!!!!!!!!
Ride it and enjoy.
I have a 2001 ktm 300 exc and do a lot of trail riding so it doesn't get a lot of Rev time. the bike runs amazing and has tons of power but after riding in tight trails, when you get on the throttle it takes a while for it to get its power back, have to run it through the gears before it runs right again. also it smokes heavily when running it at low rpms for a while. I pulled my plug and it has a ton of carbon build up on it. could it just be my pilot circuit it way too rich?
The main jet is too big.
hi i have a yamaha dt 125 1996 and im having problems getting it to start ive cleaned the carb out and the jets and the reeds and nothing is working ive got good spark and ive changed the top end on it. but when you put fuel down the cylinder head it fires and goes for a few seconds then dies could you please help me many thanks.
hii i need some help. i just finished rebuilding my bike and when i rev it 3/4 to full throttle it stops running. i have a yz85 with a 140 main jet do i need a bigger jet ?
@This0is0pointless nvm,i had it backwards,the pilot jet controls fuel only and the air screw of course only controls air which mix's with the fuel in the pilot circuit.simpler then i thought,i ended up finding out my pilot jet was just clogged anyway lol
I've tried to adjust my 300(2011). I rode it last spring/summer when i bought it. It was running maybe too rich so i made it leaner. Comes the autumn and its still probably too lean. Feels like its getting very hot. Idle starts to be "restless" when hot.
But rich or lean, one problem is there always. The damn exhaust (mainly the expansion chamber) so f***ing hot! Bike had nice brand new chrome exhaust when I got it, it instantly went to being "tempered". I can easily light a cigarette even from the fattest part, and its full of marks of my shoes etc. melting on it.
Some say that when its lean, it runs hot. But even in the summer when it was too rich...
Any ideas?
To lean man
i got a gilera sc 125, it warms up and runs when i turn the choke on but when i turn it off and drive down the road and i stop it doesnt idle and turns off? what could the problem be ?