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

ohio_tx300 wrote:

Genuine question about race gas. What makes it worth the extra cost? Never had the chance to ask anyone before. I understand how it reduces the...

Genuine question about race gas. What makes it worth the extra cost? Never had the chance to ask anyone before. I understand how it reduces the risk of detonation. Do you all race and it helps with the hunt for every last hp?

Braaaphole wrote:

I picked up a TC 125 a couple weeks ago and need to adjust the jetting on it. Keep in mind, this is a fully built...

I picked up a TC 125 a couple weeks ago and need to adjust the jetting on it. Keep in mind, this is a fully built factory bike, so I'm uncertain what is done to it jetting wise. I pulled the float bowl off this morning to check the jet sizes. Pilot is 35 and main is 480. I've ordered and assortment of jets so I can dial it in.
Mid to top felt great, down low was a little rich and would load up pretty fast. Dropping to a 32.5 should clean that up.

Is there any way to tell what needle and slide are in it? Not sure if there are any markings to look for or measurements.
I need to check the needle jet too and see what it is.

Right now the bike is setup for and running MRX02, but I will be switching it to T2 because no one around here carries MRX02. My understanding is I should lean each jet at least 1 size for the fuel change. I will run the T2 with the jetting as is first and see.

Bruce372 wrote:

More questions....

Jd is out of 5 slides... anywhere else sell them?

Is the 5.5 kawi slide too lean for 125, 150?

Thanks

Bruce372 wrote:

Thanks guys, I just checked and the 2018 sx150 carb does indeed have the S4 nozzle. I will wait for a 5 slide to become available...

Thanks guys, I just checked and the 2018 sx150 carb does indeed have the S4 nozzle.

I will wait for a 5 slide to become available, ive cut them before in the past.

So with a 5 slide, 490 main 32.5 pilot and which needle?

Cheers, bruce

Braaaphole wrote:

I picked up a TC 125 a couple weeks ago and need to adjust the jetting on it. Keep in mind, this is a fully built...

I picked up a TC 125 a couple weeks ago and need to adjust the jetting on it. Keep in mind, this is a fully built factory bike, so I'm uncertain what is done to it jetting wise. I pulled the float bowl off this morning to check the jet sizes. Pilot is 35 and main is 480. I've ordered and assortment of jets so I can dial it in.
Mid to top felt great, down low was a little rich and would load up pretty fast. Dropping to a 32.5 should clean that up.

Is there any way to tell what needle and slide are in it? Not sure if there are any markings to look for or measurements.
I need to check the needle jet too and see what it is.

Right now the bike is setup for and running MRX02, but I will be switching it to T2 because no one around here carries MRX02. My understanding is I should lean each jet at least 1 size for the fuel change. I will run the T2 with the jetting as is first and see.

Bruce372 wrote:

Thanks guys, I just checked and the 2018 sx150 carb does indeed have the S4 nozzle. I will wait for a 5 slide to become available...

Thanks guys, I just checked and the 2018 sx150 carb does indeed have the S4 nozzle.

I will wait for a 5 slide to become available, ive cut them before in the past.

So with a 5 slide, 490 main 32.5 pilot and which needle?

Cheers, bruce

digger wrote:

A 5.5 slide, IMO, is going to be a little lean to be used in the small bore 125/150 bikes. If you don't want to cut...

A 5.5 slide, IMO, is going to be a little lean to be used in the small bore 125/150 bikes. If you don't want to cut your oem slide, I believe this is the Suzuki oem part# for their #5 slide. https://www.partzilla.com/product/suzuki/13551-36F50?ref=6aabbb39404040…

Here is an aftermarket supplier for a #5 slide as well. https://www.frankmxparts.com/epages/62910900.sf/en_US/?ObjectPath=/Shop…

I don't know if either one of those part #'s are in stock at this time. I'm just giving you options.

As far as the needle goes for this time of year, what type of temps and or elevation are you looking at ? The pilot and main will be jetted around it.

fredmotokx wrote:

Hi guys, I am the new owner of a ktm 150sx 2021 and new to two-stroke carb engine. Following this thread recommendation, I made some adjustments...

Hi guys, I am the new owner of a ktm 150sx 2021 and new to two-stroke carb engine.

Following this thread recommendation, I made some adjustments to the jetting for this weekend practice.

Needle pos 2 (from 3 stock)
Idle jet 32.5 (from 30 stock)
Main jet 490 (from 470 stock)
Airscrew 1.5 stock
Needle 42-71 stock
Needle Jet S4 stock
Slide #4 stock
Pump 91

The temperature was around 50f, maybe a bit colder in the morning. The track condition was really soft, a lot of sand going out of the corner.

The bike never had this power exiting corners before, was night and day difference. It was way faster rolling out of the corner too.

Looking forward to changing the slide for a #5 and JD gasket kit for peace of mind.
With the #5 slide do you guys think I will need to do small change to the rest of the setup or it's should be close?

Does the outside temperature affect allot the jetting on our bike? (95 % of our riding temperature out here is between 50f to 80f)

Thank you for making this thread, such a nice source of information for our Mikuni carb.

Bruce372 wrote:

Thanks digger.

70f sea level mx in California.

Bruce372 wrote:

Thanks digger.

70f sea level mx in California.

digger wrote:

I would start off with a 42-74 in clip #2, 32.5 pilot and 490 main. This is to be used with the S-4 and #5 slide...

I would start off with a 42-74 in clip #2, 32.5 pilot and 490 main. This is to be used with the S-4 and #5 slide. This is assuming you have already replaced the jet block gasket.

digger wrote:

Good idea. I like to also modify the front side of the slide as well, it’s not absolutely necessary, but it does help out the pilot...

Good idea. I like to also modify the front side of the slide as well, it’s not absolutely necessary, but it does help out the pilot circuit, but it may require that you use a 30 pilot.

fredmotokx wrote:

Hi guys, I am the new owner of a ktm 150sx 2021 and new to two-stroke carb engine. Following this thread recommendation, I made some adjustments...

Hi guys, I am the new owner of a ktm 150sx 2021 and new to two-stroke carb engine.

Following this thread recommendation, I made some adjustments to the jetting for this weekend practice.

Needle pos 2 (from 3 stock)
Idle jet 32.5 (from 30 stock)
Main jet 490 (from 470 stock)
Airscrew 1.5 stock
Needle 42-71 stock
Needle Jet S4 stock
Slide #4 stock
Pump 91

The temperature was around 50f, maybe a bit colder in the morning. The track condition was really soft, a lot of sand going out of the corner.

The bike never had this power exiting corners before, was night and day difference. It was way faster rolling out of the corner too.

Looking forward to changing the slide for a #5 and JD gasket kit for peace of mind.
With the #5 slide do you guys think I will need to do small change to the rest of the setup or it's should be close?

Does the outside temperature affect allot the jetting on our bike? (95 % of our riding temperature out here is between 50f to 80f)

Thank you for making this thread, such a nice source of information for our Mikuni carb.

Bruce372 wrote:

Hey Fred, did you test the 5 slide and if so, how does it compare to this setup?

Bruce372 wrote:

Hey guys, quick update. I ran the mikuni on my 2018 150 today. Ironically, its the first time I've used the stock carb on this bike...

Hey guys, quick update. I ran the mikuni on my 2018 150 today. Ironically, its the first time I've used the stock carb on this bike (bought it used with lectron)

Anyhow, 490 main, s4 nozzle and 42,74 needle #3, 32.5 pilot worked good. I had cut the slide myself and I don't like doing this since it can lack precision and reproducibility...

However, bike ran pretty good. Slightly rich so went one leaner on thr needle. With this setting its really clean and carburets well. Slight richness on the very lowest throttle setting, maybe that would clean up with more grinding on the slide cut out, front notch or a one size thicker needle... matters not, can't be bothered lol. Aside, from 1/8 throttle to wide open its clean and well metered power.

Better than the lectron (from memory)... but not the rip snorting mega power the stic provides... although, the bike is more confidence inspiring given a couple of issues I've had with fueling with the pwk keihin.

Thanks everyone for help and feedback

Bruce372 wrote:

Hey guys, quick update. I ran the mikuni on my 2018 150 today. Ironically, its the first time I've used the stock carb on this bike...

Hey guys, quick update. I ran the mikuni on my 2018 150 today. Ironically, its the first time I've used the stock carb on this bike (bought it used with lectron)

Anyhow, 490 main, s4 nozzle and 42,74 needle #3, 32.5 pilot worked good. I had cut the slide myself and I don't like doing this since it can lack precision and reproducibility...

However, bike ran pretty good. Slightly rich so went one leaner on thr needle. With this setting its really clean and carburets well. Slight richness on the very lowest throttle setting, maybe that would clean up with more grinding on the slide cut out, front notch or a one size thicker needle... matters not, can't be bothered lol. Aside, from 1/8 throttle to wide open its clean and well metered power.

Better than the lectron (from memory)... but not the rip snorting mega power the stic provides... although, the bike is more confidence inspiring given a couple of issues I've had with fueling with the pwk keihin.

Thanks everyone for help and feedback

digger wrote:

I’m not sure how precise you were on cutting the slide, but a lot of times when you cut the back side and notch the front...

I’m not sure how precise you were on cutting the slide, but a lot of times when you cut the back side and notch the front you’ll need to use a smaller pilot jet, like i mentioned above. Try a 30 pilot jet and or try adjusting the air screw.

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...

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 4/19/23**
'17+ 125/150 jetting (‘22 bikes have a known bog, there is no jetting or carb swap combo yet that takes care of that problem. If or when it gets figured out I’ll update)

MJ 510
PJ 32.5
AS 1.75
slide 5.0 from JD Jetting
Needle 42-74 on the 2nd clip (Yamaha 284-14116-H4-00)
Needle jet S4 (KTM part #55431021400)
PV 2.25 turns in from all the way out.
Fuel mix 40:1

(credit to FGR01 for continuing to refine the small bore jetting)

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

300sx jetting

Pilot jet 25 and main jet 460 to start.
Slide 5.5 (Kawasaki part 16025-0002)
Needle 42-75 on the 2nd clip (Yamaha part #284-14116-H5-00)
5/32” chainsaw file to notch the front of the slide.
A/S 1.5 to start, you’ll need to adjust as needed.