KTM/HUS 125/150/250 jetting thread

AJ565 wrote:

I get a lot of emails from here and at the track about jetting for the 2 strokes. Thanks to digger for pointing me in the right direction this is the currant specs. I have for everything. Its easier to start a thread With all the jetting in it to keep track of everything. Your jetting might need tweaked based on your temps and elevation, but this is a good start for you.

**Updated 7/28/2020**
'17+ 125/150 jetting
Pump gas/race gas mix, C12 straight
MJ 490
PJ 32.5
Needle Jet S4
AS 1.5
slide 5.0
Needle 42-74 on the 2nd clip (Yamaha 284-14116-H4-00)
Needle jet S4 (KTM part #55431021400)
PV 1.75 turns in from all the way out.
Fuel mix 40:1

On the '17+ 250's **Updated 10/13/2020**
Pump gas/race gas or straight C12

This is my current jetting. Its more refined all around and crisp down low with better top end over rev.

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

OR

Solid jetting if you're someone that doesn't live on top end. Crisp down low out of turns pull.
MJ 490
PJ 32.5
AS 1.5 turns out
Needle jet S4 (KTM part #55431021400) stock is S1
Needle 42-75 on the 2nd clip (Yamaha part #284-14116-H5-00)
Slide 5.5 (Kawasaki part 16025-0002)
PV 1.75 turns in from all the way out
Fuel mix 50:1

Do you have any good jetting specs for the 2018 KTM SX 150 without changing the slide?

Jayklash wrote:

Do you have any good jetting specs for the 2018 KTM SX 150 without changing the slide?

Nope, the slide is the key to making the run right. You can modify your own slide with a dermal tool if you don't want to spend the money. The specs. are in a few threads on here about what measurements you need.

Will this slide fit?

Jayklash wrote:

Will this slide fit?

No, that’s a different carb. I’m not sure where to get a 5.0 slide. Maybe digger will see this thread and chime in on where to find one.

rocky mountain parts
kx 125 fiche should have the 5.0 slide

JD jetting has a 5.0 on their website. The richest kx125 slide was a 5.5 and I felt like it was a little too lean.

jwolfman317 wrote:

JD jetting has a 5.0 on their website. The richest kx125 slide was a 5.5 and I felt like it was a little too lean.

Larger the number means there is more air coming through the opening = leaner

jwolfman317 wrote:

JD jetting has a 5.0 on their website. The richest kx125 slide was a 5.5 and I felt like it was a little too lean.

garagedog wrote:

Larger the number means there is more air coming through the opening = leaner

They offer a 5.5, 5.75, and 6.0 for a kx 125; therefore, the 5.5 is the richest that is offered, yet still too lean for our bike. That is why I went with the 5.0 from JD Jetting.

The best 125/150 jetting setup that I have come up with is:

42-74 needle start out in the #2 clip position https://www.motosport.com/oem-parts/part-number/284-14116-h4-00?mmysource=yamaha;yz125;2019&partgroup=carburetor

S-4 needle jet

#5-slide, it's a must have item. IMO,


#5.5-#6 slides are to lean for the small bore bikes. You can either cut your #4 oem yourself, or you can purchase one from JD jetting.
https://jdjetting.com/product/jdmk02-mikuni-tmx-ktm-husq-carburetor-slide-5/

Main. 490

32.5--pilot
if you notch the front side of the slide, you will need a 30 pilot

You will also more than likely need a jet block gasket, as the oem ones deform over a very short amount of time.

https://jdjetting.com/product/jdmk05-mikuni-tmx-jet-block-kit/

air screw at 1.5 turns out to begin with.

Digger, do you have the slide measurements to cut a 4.0 to a 5.0?

digger wrote:

The best 125/150 jetting setup that I have come up with is:

42-74 needle start out in the #2 clip position https://www.motosport.com/oem-parts/part-number/284-14116-h4-00?mmysource=yamaha;yz125;2019&partgroup=carburetor

S-4 needle jet

#5-slide, it's a must have item. IMO,


#5.5-#6 slides are to lean for the small bore bikes. You can either cut your #4 oem yourself, or you can purchase one from JD jetting.
https://jdjetting.com/product/jdmk02-mikuni-tmx-ktm-husq-carburetor-slide-5/

Main. 490

32.5--pilot
if you notch the front side of the slide, you will need a 30 pilot

You will also more than likely need a jet block gasket, as the oem ones deform over a very short amount of time.

https://jdjetting.com/product/jdmk05-mikuni-tmx-jet-block-kit/

air screw at 1.5 turns out to begin with.

Thanks for the info, digger. What temp and elevation are these settings good for? Also, what main jet do you recommmend along with these settings?

I am running jetting that Aj suggests. The bike runs great but is running way too hot. I bumped the MJ up to a 490. Should I go to a richer slide keep going up in MJ?

jpatz319 wrote:

I am running jetting that Aj suggests. The bike runs great but is running way too hot. I bumped the MJ up to a 490. Should I go to a richer slide keep going up in MJ?

What gas are you running and mixed at what? You can only go up so much with a MJ before it will start to run poor. Unless you're always wide open you may need to drop to a 5.5 slide. My bike also has a 490 in it, but I'm also running u4.4 mixed 44:1.

I have a slide I cut that should be around 5.5 that I can put in my bike and test with and get some solid numbers. It will be a week or so as my suspension is off getting redone.

I'm running 50/50 C12 and pump at 60:1. I do ride the bike like a 125 wide open everywhere. I was thinking about running 40:1 and changing the jetting if it is too rich. Do you have the specs for a 5.5? I have my stock slide and can cut to match.

jpatz319 wrote:

I'm running 50/50 C12 and pump at 60:1. I do ride the bike like a 125 wide open everywhere. I was thinking about running 40:1 and changing the jetting if it is too rich. Do you have the specs for a 5.5? I have my stock slide and can cut to match.

I ride mine like a 125 too lol.

40:1 is more oil so it would be leaner fuel mix. I think so, digger posted in another thread 1.5mm deeper and wider on the cut to turn a 4.0 into a 5.5. I have one that I cut that next time I go ride I'll swap into it and see what happens and if I have to change any other jetting. I have a 500 MJ that I need to try also.

digger wrote:

The best 125/150 jetting setup that I have come up with is:

42-74 needle start out in the #2 clip position https://www.motosport.com/oem-parts/part-number/284-14116-h4-00?mmysource=yamaha;yz125;2019&partgroup=carburetor

S-4 needle jet

#5-slide, it's a must have item. IMO,


#5.5-#6 slides are to lean for the small bore bikes. You can either cut your #4 oem yourself, or you can purchase one from JD jetting.
https://jdjetting.com/product/jdmk02-mikuni-tmx-ktm-husq-carburetor-slide-5/

Main. 490

32.5--pilot
if you notch the front side of the slide, you will need a 30 pilot

You will also more than likely need a jet block gasket, as the oem ones deform over a very short amount of time.

https://jdjetting.com/product/jdmk05-mikuni-tmx-jet-block-kit/

air screw at 1.5 turns out to begin with.

So do you only need the jet block gasket if you notch the slide yourself? Also what temp and elevation is this good for? I'm in the uk

digger wrote:

The best 125/150 jetting setup that I have come up with is:

42-74 needle start out in the #2 clip position https://www.motosport.com/oem-parts/part-number/284-14116-h4-00?mmysource=yamaha;yz125;2019&partgroup=carburetor

S-4 needle jet

#5-slide, it's a must have item. IMO,


#5.5-#6 slides are to lean for the small bore bikes. You can either cut your #4 oem yourself, or you can purchase one from JD jetting.
https://jdjetting.com/product/jdmk02-mikuni-tmx-ktm-husq-carburetor-slide-5/

Main. 490

32.5--pilot
if you notch the front side of the slide, you will need a 30 pilot

You will also more than likely need a jet block gasket, as the oem ones deform over a very short amount of time.

https://jdjetting.com/product/jdmk05-mikuni-tmx-jet-block-kit/

air screw at 1.5 turns out to begin with.

Jayklash wrote:

So do you only need the jet block gasket if you notch the slide yourself? Also what temp and elevation is this good for? I'm in the uk

Yes, if you cut and notch your oem slide you will only need the jet block gasket kit from JD.

That setup has been used from 60f to 90f with slight air screw adjustments only. Sea level to 2000’

digger wrote:

The best 125/150 jetting setup that I have come up with is:

42-74 needle start out in the #2 clip position https://www.motosport.com/oem-parts/part-number/284-14116-h4-00?mmysource=yamaha;yz125;2019&partgroup=carburetor

S-4 needle jet

#5-slide, it's a must have item. IMO,


#5.5-#6 slides are to lean for the small bore bikes. You can either cut your #4 oem yourself, or you can purchase one from JD jetting.
https://jdjetting.com/product/jdmk02-mikuni-tmx-ktm-husq-carburetor-slide-5/

Main. 490

32.5--pilot
if you notch the front side of the slide, you will need a 30 pilot

You will also more than likely need a jet block gasket, as the oem ones deform over a very short amount of time.

https://jdjetting.com/product/jdmk05-mikuni-tmx-jet-block-kit/

air screw at 1.5 turns out to begin with.

jwolfman317 wrote:

Thanks for the info, digger. What temp and elevation are these settings good for? Also, what main jet do you recommmend along with these settings?

I have them setup with a 490 main. Make sure you use Mikuni brand mains only. The quality of the aftermarket mains above 490 varies wildly. I have seen 520 aftermarket mains that ran leaner than 490’s. Just be advised.

AJ565 wrote:

Digger, do you have the slide measurements to cut a 4.0 to a 5.0?

I dykem blue the back side of the slide where I will be cutting, so that I can see the etched line. I then etch the amount I need to take off around the full arch, 1mm to go from an OEM 4.0 to a 5.0, or 1.5mm to go from 4.0 to a 5.5 etc , into the slide with a caliper. I then grind and blend down to the etched line. I finish(smooth) it up with a sanding drum.

digger wrote:

The best 125/150 jetting setup that I have come up with is:

42-74 needle start out in the #2 clip position https://www.motosport.com/oem-parts/part-number/284-14116-h4-00?mmysource=yamaha;yz125;2019&partgroup=carburetor

S-4 needle jet

#5-slide, it's a must have item. IMO,


#5.5-#6 slides are to lean for the small bore bikes. You can either cut your #4 oem yourself, or you can purchase one from JD jetting.
https://jdjetting.com/product/jdmk02-mikuni-tmx-ktm-husq-carburetor-slide-5/

Main. 490

32.5--pilot
if you notch the front side of the slide, you will need a 30 pilot

You will also more than likely need a jet block gasket, as the oem ones deform over a very short amount of time.

https://jdjetting.com/product/jdmk05-mikuni-tmx-jet-block-kit/

air screw at 1.5 turns out to begin with.

Jayklash wrote:

So do you only need the jet block gasket if you notch the slide yourself? Also what temp and elevation is this good for? I'm in the uk

digger wrote:

Yes, if you cut and notch your oem slide you will only need the jet block gasket kit from JD.

That setup has been used from 60f to 90f with slight air screw adjustments only. Sea level to 2000’

I am trying to source a 5.0 slide here in the UK but they do not look the same as one pictured on JD jetting site. Is the slide actually for a keihin carb? But fits a mikuni?

The slide pictured on JD's website is the correct slide for a Mikuni TMX-x carb( the slide you need) . A Mikuni TMX-x slide will only work in a Mikuni TMX-x carb. JD's slides will only work in non TPS Mikuni's, which with your KTM, you don't have to worry about.

Ok I am still going to try and sort one in the UK as shipping from the US is about $60 so nearly as much as the slide itself.

digger wrote:

The slide pictured on JD's website is the correct slide for a Mikuni TMX-x carb( the slide you need) . A Mikuni TMX-x slide will only work in a Mikuni TMX-x carb. JD's slides will only work in non TPS Mikuni's, which with your KTM, you don't have to worry about.

Pretty sure I have found one here in the UK here are a couple of pictures can you confirm for me please?

digger wrote:

The slide pictured on JD's website is the correct slide for a Mikuni TMX-x carb( the slide you need) . A Mikuni TMX-x slide will only work in a Mikuni TMX-x carb. JD's slides will only work in non TPS Mikuni's, which with your KTM, you don't have to worry about.

Jayklash wrote:

Pretty sure I have found one here in the UK here are a couple of pictures can you confirm for me please?

The slides that are in the pics, are for a Mikuni TMX-x carb, and are what you need. The bottom pic is of an oem #4 slide, exactly like the one you have in your bike now.

digger wrote:

The slide pictured on JD's website is the correct slide for a Mikuni TMX-x carb( the slide you need) . A Mikuni TMX-x slide will only work in a Mikuni TMX-x carb. JD's slides will only work in non TPS Mikuni's, which with your KTM, you don't have to worry about.

Jayklash wrote:

Pretty sure I have found one here in the UK here are a couple of pictures can you confirm for me please?

digger wrote:

The slides that are in the pics, are for a Mikuni TMX-x carb, and are what you need. The bottom pic is of an oem #4 slide, exactly like the one you have in your bike now.

Just spoke to the guy again and he said the picture is just for reference he has the same slide in a 5.0

Jayklash wrote:

Just spoke to the guy again and he said the picture is just for reference he has the same slide in a 5.0

That’s the one you need.

digger wrote:

The slides that are in the pics, are for a Mikuni TMX-x carb, and are what you need. The bottom pic is of an oem #4 slide, exactly like the one you have in your bike now.

Jayklash wrote:

Just spoke to the guy again and he said the picture is just for reference he has the same slide in a 5.0

digger wrote:

That’s the one you need.

I am trying to source one direct from mikuni as it is much cheaper. But they said they need the exact dimensions of the slide do you happen to know what they are please?

AJ565 wrote:

I ride mine like a 125 too lol.

40:1 is more oil so it would be leaner fuel mix. I think so, digger posted in another thread 1.5mm deeper and wider on the cut to turn a 4.0 into a 5.5. I have one that I cut that next time I go ride I'll swap into it and see what happens and if I have to change any other jetting. I have a 500 MJ that I need to try also.

Okay. Do you think you would have to change the needle at all to go along with the slide change?

jpatz319 wrote:

Okay. Do you think you would have to change the needle at all to go along with the slide change?

As in the needle its self or clip position? I doubt either one, but for sure not the needle its self.