125/150/250/300 KTM/HUS/GG jetting thread

Hammer 663s
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Forest Grove, OR US
3/31/2023 7:13am
Luca69 wrote:

We’re in Australia so temps in winter probably range from 50-80’F at a guess 

 

I find this jetting stable from about 35-90f. Below 35 I have increase the pilot and run a 520 main regardless of dirt. It doesn’t get above 90 where I live and when it does we all melt anyway. 
 

a good moto buddy of mine just moved to Sydney. I’ll be shipping his KTM 250 factory edition to him in a couple months. 

4/8/2023 3:03pm

My brother and I have new 2023 GasGas MC250s, I put the second jetting option from the front page on mine (5.5 slide, Yamaha needle, 32.5 pilot and tried 35 as well, 490MJ, AS 1.5 turns out and tried other settings as well but minimal change) and his is stock. Both bikes have 1 hour since new. We are at 600ft and it was 43 degrees when we were testing. Both running Motorex at 50:1 and same fuel, 91 octane no ethanol. 

He has a lot more bottom end pull and his idles normally while mine shuts off (recognize idle is not a focus but would be nice while I'm adjusting goggles or putting my gloves on). Any thoughts for things to try to improve bottom end? Thank you

AJ565
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4/8/2023 8:04pm
taylor797 wrote:
My brother and I have new 2023 GasGas MC250s, I put the second jetting option from the front page on mine (5.5 slide, Yamaha needle, 32.5...

My brother and I have new 2023 GasGas MC250s, I put the second jetting option from the front page on mine (5.5 slide, Yamaha needle, 32.5 pilot and tried 35 as well, 490MJ, AS 1.5 turns out and tried other settings as well but minimal change) and his is stock. Both bikes have 1 hour since new. We are at 600ft and it was 43 degrees when we were testing. Both running Motorex at 50:1 and same fuel, 91 octane no ethanol. 

He has a lot more bottom end pull and his idles normally while mine shuts off (recognize idle is not a focus but would be nice while I'm adjusting goggles or putting my gloves on). Any thoughts for things to try to improve bottom end? Thank you

Did you adjust the power valve? It needs adjusted with the jetting change since they effect each other. 

sesker15
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4/9/2023 6:31am Edited Date/Time 4/9/2023 6:33am

Hello,

Need some help guys. I have a 2022 mc125. I was running pro circuit recommend jetting. Bike ran good. 
i recently got the 150sx big bore kit for the bike. Had the cylinder and the head ported by PC. 

Here are the jetting recommendations they gave me. 
490 main jet

35 pilot

stock needle 2nd click (6bfy43-71)

air screw 2 out. 

Bike runs like crap. It falls off so bad on too it’s dangerous to ride. Bike feels super fat wide open throttle. It’s like the bike doesn’t have a power band. 
Would the jetting recommendations on page one help? 
Could it be the i need to adjust the power valve?
Thanks for the help. 

The Shop

4/9/2023 11:23am Edited Date/Time 4/9/2023 11:23am
taylor797 wrote:
My brother and I have new 2023 GasGas MC250s, I put the second jetting option from the front page on mine (5.5 slide, Yamaha needle, 32.5...

My brother and I have new 2023 GasGas MC250s, I put the second jetting option from the front page on mine (5.5 slide, Yamaha needle, 32.5 pilot and tried 35 as well, 490MJ, AS 1.5 turns out and tried other settings as well but minimal change) and his is stock. Both bikes have 1 hour since new. We are at 600ft and it was 43 degrees when we were testing. Both running Motorex at 50:1 and same fuel, 91 octane no ethanol. 

He has a lot more bottom end pull and his idles normally while mine shuts off (recognize idle is not a focus but would be nice while I'm adjusting goggles or putting my gloves on). Any thoughts for things to try to improve bottom end? Thank you

AJ565 wrote:

Did you adjust the power valve? It needs adjusted with the jetting change since they effect each other. 

Absolutely wild the change that made - I had been paying attention to the first option for jetting and when I decided to go for the second I missed that. It rips now!! Thank you very much for all the time you put into this 

1
sesker15
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4/14/2023 7:20pm
sesker15 wrote:
Hello, Need some help guys. I have a 2022 mc125. I was running pro circuit recommend jetting. Bike ran good.  i recently got the 150sx big...

Hello,

Need some help guys. I have a 2022 mc125. I was running pro circuit recommend jetting. Bike ran good. 
i recently got the 150sx big bore kit for the bike. Had the cylinder and the head ported by PC. 

Here are the jetting recommendations they gave me. 
490 main jet

35 pilot

stock needle 2nd click (6bfy43-71)

air screw 2 out. 

Bike runs like crap. It falls off so bad on too it’s dangerous to ride. Bike feels super fat wide open throttle. It’s like the bike doesn’t have a power band. 
Would the jetting recommendations on page one help? 
Could it be the i need to adjust the power valve?
Thanks for the help. 

So i put the exact jetting specs from page1 in my 2022 mc150. Bike runs like shit! Bogs/sputters from half throttle all the way to full throttle. Bike won’t even move really at full throttle. Yes, i did the jet block gasket also. 
But look at this message i received from Jd jetting. 
So i asked them “Are you guys saying that it’s actually a 6.0 slide, even though it says 5.0 on it?”

Waiting to hear back from them ,for a response. 
i am really thinking about putting the bike back to stock. It’s unrideable with this 150 kit  bummerIMG 7724

 

gahooligan
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4/15/2023 4:48am
sesker15 wrote:
Hello, Need some help guys. I have a 2022 mc125. I was running pro circuit recommend jetting. Bike ran good.  i recently got the 150sx big...

Hello,

Need some help guys. I have a 2022 mc125. I was running pro circuit recommend jetting. Bike ran good. 
i recently got the 150sx big bore kit for the bike. Had the cylinder and the head ported by PC. 

Here are the jetting recommendations they gave me. 
490 main jet

35 pilot

stock needle 2nd click (6bfy43-71)

air screw 2 out. 

Bike runs like crap. It falls off so bad on too it’s dangerous to ride. Bike feels super fat wide open throttle. It’s like the bike doesn’t have a power band. 
Would the jetting recommendations on page one help? 
Could it be the i need to adjust the power valve?
Thanks for the help. 

sesker15 wrote:
So i put the exact jetting specs from page1 in my 2022 mc150. Bike runs like shit! Bogs/sputters from half throttle all the way to full...

So i put the exact jetting specs from page1 in my 2022 mc150. Bike runs like shit! Bogs/sputters from half throttle all the way to full throttle. Bike won’t even move really at full throttle. Yes, i did the jet block gasket also. 
But look at this message i received from Jd jetting. 
So i asked them “Are you guys saying that it’s actually a 6.0 slide, even though it says 5.0 on it?”

Waiting to hear back from them ,for a response. 
i am really thinking about putting the bike back to stock. It’s unrideable with this 150 kit  bummerIMG 7724

 

Not throwing shade on these setups at all they work great for some people. They didnt work for me. If you seach for my posts you will find the jetting I installed that was recommended from a ktm tech with a lot of experience. His jetting works awesome for me. I have the jetting and slide from this post sitting in a box. I may give it another go but really dont have a reason to now. I also went to a red PV spring with almost zero preload on the adjustment screw. 

FGR01
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4/16/2023 9:00am
sesker15 wrote:
Hello, Need some help guys. I have a 2022 mc125. I was running pro circuit recommend jetting. Bike ran good.  i recently got the 150sx big...

Hello,

Need some help guys. I have a 2022 mc125. I was running pro circuit recommend jetting. Bike ran good. 
i recently got the 150sx big bore kit for the bike. Had the cylinder and the head ported by PC. 

Here are the jetting recommendations they gave me. 
490 main jet

35 pilot

stock needle 2nd click (6bfy43-71)

air screw 2 out. 

Bike runs like crap. It falls off so bad on too it’s dangerous to ride. Bike feels super fat wide open throttle. It’s like the bike doesn’t have a power band. 
Would the jetting recommendations on page one help? 
Could it be the i need to adjust the power valve?
Thanks for the help. 

sesker15 wrote:
So i put the exact jetting specs from page1 in my 2022 mc150. Bike runs like shit! Bogs/sputters from half throttle all the way to full...

So i put the exact jetting specs from page1 in my 2022 mc150. Bike runs like shit! Bogs/sputters from half throttle all the way to full throttle. Bike won’t even move really at full throttle. Yes, i did the jet block gasket also. 
But look at this message i received from Jd jetting. 
So i asked them “Are you guys saying that it’s actually a 6.0 slide, even though it says 5.0 on it?”

Waiting to hear back from them ,for a response. 
i am really thinking about putting the bike back to stock. It’s unrideable with this 150 kit  bummerIMG 7724

 

What size number is stamped on the slide you got?

sesker15
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4/16/2023 9:32am
FGR01 wrote:

What size number is stamped on the slide you got?

It’s says 5.0 on the slide

FGR01
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4/16/2023 1:32pm
FGR01 wrote:

What size number is stamped on the slide you got?

sesker15 wrote:

It’s says 5.0 on the slide

Hmmm.  So it's not exactly clear from them, are they saying they got #6 slides in place of #5 slides, or they got slides that are stamped #5 but really have a larger #6 cutout?

I wonder how long they've been having this mixup.  For comparison, I just measured a #5 I got from them about 3-4 months ago.  It measures 7.6mm from level to the top of the cutout arch.

sesker15
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4/16/2023 2:15pm
FGR01 wrote:
Hmmm.  So it's not exactly clear from them, are they saying they got #6 slides in place of #5 slides, or they got slides that are...

Hmmm.  So it's not exactly clear from them, are they saying they got #6 slides in place of #5 slides, or they got slides that are stamped #5 but really have a larger #6 cutout?

I wonder how long they've been having this mixup.  For comparison, I just measured a #5 I got from them about 3-4 months ago.  It measures 7.6mm from level to the top of the cutout arch.

That’s the exact same question i email JD jetting. Still waiting on a response. I will share once i hear back from them. Here are some measurements from the “5.0” i just received. 
IMG 7760

 IMG 7759

 IMG 7758 0

 

FGR01
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4/16/2023 3:30pm
FGR01 wrote:
Hmmm.  So it's not exactly clear from them, are they saying they got #6 slides in place of #5 slides, or they got slides that are...

Hmmm.  So it's not exactly clear from them, are they saying they got #6 slides in place of #5 slides, or they got slides that are stamped #5 but really have a larger #6 cutout?

I wonder how long they've been having this mixup.  For comparison, I just measured a #5 I got from them about 3-4 months ago.  It measures 7.6mm from level to the top of the cutout arch.

sesker15 wrote:
That’s the exact same question i email JD jetting. Still waiting on a response. I will share once i hear back from them. Here are some...

That’s the exact same question i email JD jetting. Still waiting on a response. I will share once i hear back from them. Here are some measurements from the “5.0” i just received. 
IMG 7760

 IMG 7759

 IMG 7758 0

 

OK.. that looks the same as the one from a few months ago.  For more comparison, I pulled the #5 out of another bike that rips.  Bought this one almost 3 years ago.  Also looks the same as these recent ones.  So it will be interesting to see what the prob is JD is talking about.

JD Mikuni num 5 slide

 

sesker15
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4/17/2023 8:28pm
FGR01 wrote:
Hmmm.  So it's not exactly clear from them, are they saying they got #6 slides in place of #5 slides, or they got slides that are...

Hmmm.  So it's not exactly clear from them, are they saying they got #6 slides in place of #5 slides, or they got slides that are stamped #5 but really have a larger #6 cutout?

I wonder how long they've been having this mixup.  For comparison, I just measured a #5 I got from them about 3-4 months ago.  It measures 7.6mm from level to the top of the cutout arch.

sesker15 wrote:
That’s the exact same question i email JD jetting. Still waiting on a response. I will share once i hear back from them. Here are some...

That’s the exact same question i email JD jetting. Still waiting on a response. I will share once i hear back from them. Here are some measurements from the “5.0” i just received. 
IMG 7760

 IMG 7759

 IMG 7758 0

 

FGR01 wrote:
OK.. that looks the same as the one from a few months ago.  For more comparison, I pulled the #5 out of another bike that rips. ...

OK.. that looks the same as the one from a few months ago.  For more comparison, I pulled the #5 out of another bike that rips.  Bought this one almost 3 years ago.  Also looks the same as these recent ones.  So it will be interesting to see what the prob is JD is talking about.

JD Mikuni num 5 slide

 

Update from jd jetting. IMG 7771.jpeg?VersionId=zSukni6BOFj lMj6HjaeqRE

 

1
kpersonius264
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4/19/2023 6:10pm

So I just read through all 32 pages over the course of a few days and was all excited to try the setup on the first page only to find out it doesn't with with the 22+ bikes?

I just picked up a new to me 22 tc 125 with 17 hours. I had everything in my cart ready to order, but should I hold off? I mostly ride my 450 but iv'e had an 04yz125 for about 10 years that I often play on and this stock husky is lightyears faster as is so its hard for me to tell if it's running as it should. (iv'e never been one to nitpick jetting due to my lack of knowledge)

I haven’t opened up the carb to see what jets are in it, but it starts up very easily without the choke, will load up a little bit while warming it up on the stand but it will clear out pretty easily, and seems to fall a little flat up top on over rev. I THINK the only time the bike bogs is just to me being lazy and not down shifting, however the bike recovers well with a little clutch work.

 

Long story short, do I try the page one jetting specs or just forget about it?

AJ565
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San Antonio, TX US
4/19/2023 6:56pm
So I just read through all 32 pages over the course of a few days and was all excited to try the setup on the first...

So I just read through all 32 pages over the course of a few days and was all excited to try the setup on the first page only to find out it doesn't with with the 22+ bikes?

I just picked up a new to me 22 tc 125 with 17 hours. I had everything in my cart ready to order, but should I hold off? I mostly ride my 450 but iv'e had an 04yz125 for about 10 years that I often play on and this stock husky is lightyears faster as is so its hard for me to tell if it's running as it should. (iv'e never been one to nitpick jetting due to my lack of knowledge)

I haven’t opened up the carb to see what jets are in it, but it starts up very easily without the choke, will load up a little bit while warming it up on the stand but it will clear out pretty easily, and seems to fall a little flat up top on over rev. I THINK the only time the bike bogs is just to me being lazy and not down shifting, however the bike recovers well with a little clutch work.

 

Long story short, do I try the page one jetting specs or just forget about it?

Honestly that’s gonna be your call. I just updated the 125 jetting a few minutes ago with a better setting that FCR01 has been testing that’s a good starting point. The ‘22 engines have that known bog, but it seems that not all of them have it or some people just don’t notice it because they don’t ride in that rev range that it happens in. 

kpersonius264
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4/20/2023 6:03pm

FF156A0F-1588-492D-B26C-529FDD4E152B.jpeg?VersionId=oAoND

 A67B4928-6905-4213-A0DF-B4778F0F3D60

  No surprise here… Changed the jet block gasket while going through the carb to see what I have. 

here is what is in the carb now. Note: it may or may not be Oem jetting as i just bought the bike used. 
 

Main: 500 

pilot: 35

air screw 1.75

Slide#4

needle: 43-71 2nd pos

i am assuming have an s-7 needle jet, but it’s very stuck. From what I understand is I am just supposed to push it down from the top of the carb and it will fall out. By I have been very careful not to damage the brass but no luck. I used the plastic handle of a screwdriver to pry down on it but it won’t budge. What do I have to do to get this thing out?

as for float height I am still not clear how to measure it. Is there a anyone who can explain it to me like you would to a toddler? I’m a hands on learner so it’s hard for me to understand via reading a forum sometimes  

 

FGR01
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4/20/2023 7:08pm
    No surprise here… Changed the jet block gasket while going through the carb to see what I have.  here is what is in the...

FF156A0F-1588-492D-B26C-529FDD4E152B.jpeg?VersionId=oAoND

 A67B4928-6905-4213-A0DF-B4778F0F3D60

  No surprise here… Changed the jet block gasket while going through the carb to see what I have. 

here is what is in the carb now. Note: it may or may not be Oem jetting as i just bought the bike used. 
 

Main: 500 

pilot: 35

air screw 1.75

Slide#4

needle: 43-71 2nd pos

i am assuming have an s-7 needle jet, but it’s very stuck. From what I understand is I am just supposed to push it down from the top of the carb and it will fall out. By I have been very careful not to damage the brass but no luck. I used the plastic handle of a screwdriver to pry down on it but it won’t budge. What do I have to do to get this thing out?

as for float height I am still not clear how to measure it. Is there a anyone who can explain it to me like you would to a toddler? I’m a hands on learner so it’s hard for me to understand via reading a forum sometimes  

 

To remove the needle-jet, not trying to be insulting but just checking the simple stuff.. you do have the  main jet and 8mm main jet holder removed first, right?  Once those are out, the needle-jet usually only needs a slight little push from the top to fall out.

 

kpersonius264
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4/20/2023 8:03pm
    No surprise here… Changed the jet block gasket while going through the carb to see what I have.  here is what is in the...

FF156A0F-1588-492D-B26C-529FDD4E152B.jpeg?VersionId=oAoND

 A67B4928-6905-4213-A0DF-B4778F0F3D60

  No surprise here… Changed the jet block gasket while going through the carb to see what I have. 

here is what is in the carb now. Note: it may or may not be Oem jetting as i just bought the bike used. 
 

Main: 500 

pilot: 35

air screw 1.75

Slide#4

needle: 43-71 2nd pos

i am assuming have an s-7 needle jet, but it’s very stuck. From what I understand is I am just supposed to push it down from the top of the carb and it will fall out. By I have been very careful not to damage the brass but no luck. I used the plastic handle of a screwdriver to pry down on it but it won’t budge. What do I have to do to get this thing out?

as for float height I am still not clear how to measure it. Is there a anyone who can explain it to me like you would to a toddler? I’m a hands on learner so it’s hard for me to understand via reading a forum sometimes  

 

FGR01 wrote:
To remove the needle-jet, not trying to be insulting but just checking the simple stuff.. you do have the  main jet and 8mm main jet holder...

To remove the needle-jet, not trying to be insulting but just checking the simple stuff.. you do have the  main jet and 8mm main jet holder removed first, right?  Once those are out, the needle-jet usually only needs a slight little push from the top to fall out.

 

Not insulting at all. Yes they are both removed. I am pushing from the top down. 

GG121
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4/21/2023 6:12am
So I just read through all 32 pages over the course of a few days and was all excited to try the setup on the first...

So I just read through all 32 pages over the course of a few days and was all excited to try the setup on the first page only to find out it doesn't with with the 22+ bikes?

I just picked up a new to me 22 tc 125 with 17 hours. I had everything in my cart ready to order, but should I hold off? I mostly ride my 450 but iv'e had an 04yz125 for about 10 years that I often play on and this stock husky is lightyears faster as is so its hard for me to tell if it's running as it should. (iv'e never been one to nitpick jetting due to my lack of knowledge)

I haven’t opened up the carb to see what jets are in it, but it starts up very easily without the choke, will load up a little bit while warming it up on the stand but it will clear out pretty easily, and seems to fall a little flat up top on over rev. I THINK the only time the bike bogs is just to me being lazy and not down shifting, however the bike recovers well with a little clutch work.

 

Long story short, do I try the page one jetting specs or just forget about it?

AJ565 wrote:
Honestly that’s gonna be your call. I just updated the 125 jetting a few minutes ago with a better setting that FCR01 has been testing that’s...

Honestly that’s gonna be your call. I just updated the 125 jetting a few minutes ago with a better setting that FCR01 has been testing that’s a good starting point. The ‘22 engines have that known bog, but it seems that not all of them have it or some people just don’t notice it because they don’t ride in that rev range that it happens in. 

What elevation is this new setting tested for?

FGR01
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4/21/2023 6:17am
So I just read through all 32 pages over the course of a few days and was all excited to try the setup on the first...

So I just read through all 32 pages over the course of a few days and was all excited to try the setup on the first page only to find out it doesn't with with the 22+ bikes?

I just picked up a new to me 22 tc 125 with 17 hours. I had everything in my cart ready to order, but should I hold off? I mostly ride my 450 but iv'e had an 04yz125 for about 10 years that I often play on and this stock husky is lightyears faster as is so its hard for me to tell if it's running as it should. (iv'e never been one to nitpick jetting due to my lack of knowledge)

I haven’t opened up the carb to see what jets are in it, but it starts up very easily without the choke, will load up a little bit while warming it up on the stand but it will clear out pretty easily, and seems to fall a little flat up top on over rev. I THINK the only time the bike bogs is just to me being lazy and not down shifting, however the bike recovers well with a little clutch work.

 

Long story short, do I try the page one jetting specs or just forget about it?

AJ565 wrote:
Honestly that’s gonna be your call. I just updated the 125 jetting a few minutes ago with a better setting that FCR01 has been testing that’s...

Honestly that’s gonna be your call. I just updated the 125 jetting a few minutes ago with a better setting that FCR01 has been testing that’s a good starting point. The ‘22 engines have that known bog, but it seems that not all of them have it or some people just don’t notice it because they don’t ride in that rev range that it happens in. 

GG121 wrote:

What elevation is this new setting tested for?

The 125/150 setting has been ran from sea level to 5,000ft in a 125.  May require small tweaks depending on exact elevation, fuel, or if it's a 150.

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FGR01
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5/1/2023 7:11am

2022 and up Mystery Bog Update

Some will recall the topic of the 2022 and 2023 (MC125) Mystery Bog when running the jetting from this thread in a 125.  Basically, quite a few folks have experienced a significant low to mid-throttle bog on the newer bikes.  The bog can be significant enough that the bike is not ridable on an MX track.  No one is totally sure why the newer bikes don't jet the same.  Some think it might be different ECU ignition mapping related to the 2022 crank issue and ECU recall.  In any case, I think I've got it licked.   

In this post I talked about how I gave up on the Mikuni and went with a Keihin on a 23 GasGas MC125.

https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/KTM-HUS-125-150-2…

I ended up much leaner on the needle than would be expected for a 125 so I went back to the Mikuni and applied that same logic.  Sure enough, a leaner needle got me in the right direction and now I've got the bike ripping on the Mikuni. I spent 3 days of trying many combos but, essentially, I ended up on the needle recommended for the 250/300 on page 1, had to raise the needle higher, bigger pilot and bigger main.

Here are the exact settings now:

2023 GasGas MC125

AvGas 100LL, Motorex at 40:1, vented airbox cover, FMF pipe and 2.1 silencer

Pilot 37.5

Main 540

Slide  JD #5, no extra notch

Needle 42-75, clip 3

Needle Jet S4

AS  1.75 out

So far have run this jetting at 80 deg/4500ft and 70-90 deg/1400ft.  Great at both.  Going to experiment a little more with the 1/2 clip richer 43-75 and a few other things just to see if it can be made more perfect but it's really good right now.  Note that if you are running fuel (pump or non-oxy) other than AvGas you likely will need leaner pilot and main than what I have.

Here's how she sounds.

 

 

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matthans1
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Flagstaff, AZ US
5/4/2023 3:18pm

Hey I got a jetting question for ya'll if you don't mind.

Just bought a 2019 KTM 250Sx that's been turned into an enduro/trail bike already. Big gas tank, 18" rear wheel, etc.

I know the 2019's SX's had different setting from the factory, and I'm getting confused about which way to go jetting wise.

If someone chimes in and says, "just buy the JD kit and do the block gasket replacement" , that's fine, but if you have some specific number for me jetting wise, that'll be cool too.   

Details....

Riding style/type: woods, tight trails, a few fire roads. Def not motocross.

Bike: No motor mods other than a fly wheel weight. (no head mods or anything, stock muffler)

Gas: I'll be trying to stick with ethanol free 91 octane pump gas

Elevation: 7k feet

Temp: usually around 60-75 deg F, really dry air normally, not humid

Thanks!!!!!

 

AJ565
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Joined
3/12/2012
Location
San Antonio, TX US
5/4/2023 6:40pm
FGR01 wrote:
2022 and up Mystery Bog Update Some will recall the topic of the 2022 and 2023 (MC125) Mystery Bog when running the jetting from this thread...

2022 and up Mystery Bog Update

Some will recall the topic of the 2022 and 2023 (MC125) Mystery Bog when running the jetting from this thread in a 125.  Basically, quite a few folks have experienced a significant low to mid-throttle bog on the newer bikes.  The bog can be significant enough that the bike is not ridable on an MX track.  No one is totally sure why the newer bikes don't jet the same.  Some think it might be different ECU ignition mapping related to the 2022 crank issue and ECU recall.  In any case, I think I've got it licked.   

In this post I talked about how I gave up on the Mikuni and went with a Keihin on a 23 GasGas MC125.

https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/KTM-HUS-125-150-2…

I ended up much leaner on the needle than would be expected for a 125 so I went back to the Mikuni and applied that same logic.  Sure enough, a leaner needle got me in the right direction and now I've got the bike ripping on the Mikuni. I spent 3 days of trying many combos but, essentially, I ended up on the needle recommended for the 250/300 on page 1, had to raise the needle higher, bigger pilot and bigger main.

Here are the exact settings now:

2023 GasGas MC125

AvGas 100LL, Motorex at 40:1, vented airbox cover, FMF pipe and 2.1 silencer

Pilot 37.5

Main 540

Slide  JD #5, no extra notch

Needle 42-75, clip 3

Needle Jet S4

AS  1.75 out

So far have run this jetting at 80 deg/4500ft and 70-90 deg/1400ft.  Great at both.  Going to experiment a little more with the 1/2 clip richer 43-75 and a few other things just to see if it can be made more perfect but it's really good right now.  Note that if you are running fuel (pump or non-oxy) other than AvGas you likely will need leaner pilot and main than what I have.

Here's how she sounds.

 

 

Keep this updated and when you’re confident with it I’ll add it to the first page. 

AJ565
Posts
2096
Joined
3/12/2012
Location
San Antonio, TX US
5/4/2023 6:44pm
matthans1 wrote:
Hey I got a jetting question for ya'll if you don't mind. Just bought a 2019 KTM 250Sx that's been turned into an enduro/trail bike already...

Hey I got a jetting question for ya'll if you don't mind.

Just bought a 2019 KTM 250Sx that's been turned into an enduro/trail bike already. Big gas tank, 18" rear wheel, etc.

I know the 2019's SX's had different setting from the factory, and I'm getting confused about which way to go jetting wise.

If someone chimes in and says, "just buy the JD kit and do the block gasket replacement" , that's fine, but if you have some specific number for me jetting wise, that'll be cool too.   

Details....

Riding style/type: woods, tight trails, a few fire roads. Def not motocross.

Bike: No motor mods other than a fly wheel weight. (no head mods or anything, stock muffler)

Gas: I'll be trying to stick with ethanol free 91 octane pump gas

Elevation: 7k feet

Temp: usually around 60-75 deg F, really dry air normally, not humid

Thanks!!!!!

 

The jetting on the first page will work for you or get it very close. I know there are a bunch of guys at 5k running the jetting, but I’m not sure about the 7k.

1
10/15/2023 5:08pm

Hey guys, 

i have a 2019 KTM SX 250 where I rebuilt the engine and now rebuilding the Carb. I just ordered a 5.0 Slide and a S4 Needle Jet. I had installed a JD Jetting Kit a while ago and now I´m not sure about the needle I will need. Can I Still run one of my JD Jetting needle or do I also need a new needle.

The Bike got a Vforce4r and a DEP Exhaust system. 
I Hope you can help me. 

 

AJ565
Posts
2096
Joined
3/12/2012
Location
San Antonio, TX US
10/15/2023 8:35pm
Hey guys,  i have a 2019 KTM SX 250 where I rebuilt the engine and now rebuilding the Carb. I just ordered a 5.0 Slide and...

Hey guys, 

i have a 2019 KTM SX 250 where I rebuilt the engine and now rebuilding the Carb. I just ordered a 5.0 Slide and a S4 Needle Jet. I had installed a JD Jetting Kit a while ago and now I´m not sure about the needle I will need. Can I Still run one of my JD Jetting needle or do I also need a new needle.

The Bike got a Vforce4r and a DEP Exhaust system. 
I Hope you can help me. 

 

You need a different needle. I’m not sure what one you’re gonna need tho with a 5.0 slide. Thats still on the rich side for the 250’s. 

10/16/2023 4:17am
Hey guys,  i have a 2019 KTM SX 250 where I rebuilt the engine and now rebuilding the Carb. I just ordered a 5.0 Slide and...

Hey guys, 

i have a 2019 KTM SX 250 where I rebuilt the engine and now rebuilding the Carb. I just ordered a 5.0 Slide and a S4 Needle Jet. I had installed a JD Jetting Kit a while ago and now I´m not sure about the needle I will need. Can I Still run one of my JD Jetting needle or do I also need a new needle.

The Bike got a Vforce4r and a DEP Exhaust system. 
I Hope you can help me. 

 

AJ565 wrote:
You need a different needle. I’m not sure what one you’re gonna need tho with a 5.0 slide. Thats still on the rich side for the...

You need a different needle. I’m not sure what one you’re gonna need tho with a 5.0 slide. Thats still on the rich side for the 250’s. 

Thanks for the help! 

I thing I will start of with my old carb settings and my old slide since my whole engine is brand new. After break in I will try the new settings with the new slide. I order the 5.0 Slide because I thought the 6.0 Slide would be to lean. I will try the lean JD Jetting Needle first and then see how it goes with the new Slide and new needle jet. 

 

TDC
Posts
199
Joined
8/4/2023
Location
HTown, TX US
10/16/2023 9:38am
Thanks for the help!  I thing I will start of with my old carb settings and my old slide since my whole engine is brand new...

Thanks for the help! 

I thing I will start of with my old carb settings and my old slide since my whole engine is brand new. After break in I will try the new settings with the new slide. I order the 5.0 Slide because I thought the 6.0 Slide would be to lean. I will try the lean JD Jetting Needle first and then see how it goes with the new Slide and new needle jet. 

 

Have you taken a look at the PC jetting web page and/or the jetting sub-forum on KTMtalk? 

Keihin conversion simplifies life. As I'm sure you've read. 

11/5/2023 10:05am Edited Date/Time 11/5/2023 11:03am

Circling back with a continued rich condition on my 2017 KTM 250sx per the spooge leaking from my silencer (and smoke from the exhaust across mid/upper RPM)

Bike has very good compression (~190psi). I ride at around 800' elevation pretty much always. 

compression

In 2021 I replaced the jet block gasket (didn't affect rich conditions) and (per this thread) and changed to the following jetting, which also hasn't really helped the rich condition:

Main jet 500
Pilot jet 32.5
Slide 5.75 (Kawasaki part#16025-0003)
Needle 43-75 (KTM part #55431134400)
Clip position #2
Needle jet S4 (KTM part #55431021400)
Air screw 1.5-2.0
Fuel 55:1

5.75 slide 0.jpg?VersionId=EqAe6


main 500 installed 0.jpg?VersionId=UBycNIcKNHvgCk.VHIY.z

 

Block seal was replaced in 2021 and still looks OK today: 

blockseal ok.jpg?VersionId=U4rJshvWVA0l16evPD


Any advice or further things to try? 

 

11/5/2023 10:24am

After posting I pulled the float valve seat out, and the O-ring fell apart the moment I put my pick tool on it. Would that O-ring leaking cause overly rich conditions in spite of jetting otherwise being to spec? 

 

float valve seat and o ring

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