2018 ktm 250sx jetting and FWW

sandman768
Profile picture for user sandman768
Posts
7972
Joined
3/21/2014
Location
Saratoga Springs, NY US
sandman768 5/8/2020 6:19pm
5/8/2020 6:19pm
Dmilkman589 wrote:
I finally have my 2018 250SX jetted perfect in my opinion, no more off idle blubber and mean grunt through entire mid range. The motor feels...
I finally have my 2018 250SX jetted perfect in my opinion, no more off idle blubber and mean grunt through entire mid range. The motor feels electric and had no dead spots at all today. Will make minor adjustments as temps change.

ADK MX, Fort Ann, NY roughly 200ft elevation
55 Deg F, May 8th 2020
Stock 2018 250sx minus pipe and V-force reeds. (I don't think it effected jetting at all in case anyone was wondering)
JD-Jetting Jet block gasket fix (Also not sure if this did anything)

37.5 Pilot
43-71 Needle, 2nd Clip from top (this clip position was the game changer)
Stock Needle Jet
450 Main
1.5-2 on air screw, just far enough out so it started idling clean
Small world.. I was there yesterday on my 18 250 Sx... just did the first top end replacement at 55-60hrs. Checked reeds, ok, checked jet block gasket, ok, but replaced anyway. Same pilot jet as you, stock needle on 3rd clip, 450 main, I have a KX125 5,75 slide. Bike rips.... 40:1 amsoil dominator. 25% 110 Sunoco & 91 non ethanol. This bike is perfect for ADK....
digger
Profile picture for user digger
Posts
801
Joined
4/1/2008
Location
Upstate, NY US
digger 5/9/2020 5:33am
5/9/2020 5:33am
sandman768 wrote:
Small world.. I was there yesterday on my 18 250 Sx... just did the first top end replacement at 55-60hrs. Checked reeds, ok, checked jet block...
Small world.. I was there yesterday on my 18 250 Sx... just did the first top end replacement at 55-60hrs. Checked reeds, ok, checked jet block gasket, ok, but replaced anyway. Same pilot jet as you, stock needle on 3rd clip, 450 main, I have a KX125 5,75 slide. Bike rips.... 40:1 amsoil dominator. 25% 110 Sunoco & 91 non ethanol. This bike is perfect for ADK....
I hear you, I live in Johnsonville.
sandman768
Profile picture for user sandman768
Posts
7972
Joined
3/21/2014
Location
Saratoga Springs, NY US
sandman768 5/9/2020 7:08am
5/9/2020 7:08am
digger wrote:
I hear you, I live in Johnsonville.
Assume the 43-71 needle is option ktm needle? Maybe I should give that a try... always looking for improvements...
digger
Profile picture for user digger
Posts
801
Joined
4/1/2008
Location
Upstate, NY US
digger 5/9/2020 11:09am
5/9/2020 11:09am
sandman768 wrote:
Assume the 43-71 needle is option ktm needle? Maybe I should give that a try... always looking for improvements...
Yes, it's an optional KTM/Yamaha needle that is quite a bit richer than what you are currently using. You may possibly need to use a needle with a starting diameter that rich in the middle of winter up here, or somewhere with an elevation that is below sea level, but other than that, it seems really rich to me for this time of year. Maybe if you were using an R-8 or S-1 needle jet, you may possibly get away with it.

The Shop

See All »
Dmilkman589
Profile picture for user Dmilkman589
Posts
3
Joined
5/8/2020
Location
Johnsonville, NY US
Dmilkman589 5/9/2020 1:34pm
5/9/2020 1:34pm
Well the stock 250sx is an S-1 so...
digger
Profile picture for user digger
Posts
801
Joined
4/1/2008
Location
Upstate, NY US
digger 5/9/2020 2:05pm
5/9/2020 2:05pm
Dmilkman589 wrote:
Well the stock 250sx is an S-1 so...
You're right they changed to an s-4 needle jet in 2019. That rich 43-71 needle was a shot at a band aid fix. Instead of replacing the S-1 for the for the richer S-4 and leaner 42-75 needle they tried to just use a richer jet needle. KTM will never replace the most expensive problem, which is the 4.0 slide.
Dmilkman589
Profile picture for user Dmilkman589
Posts
3
Joined
5/8/2020
Location
Johnsonville, NY US
Dmilkman589 5/9/2020 2:10pm
5/9/2020 2:10pm Edited Date/Time 5/9/2020 2:12pm
That’s false per any 250sx manual
opyguy
Profile picture for user opyguy
Posts
586
Joined
8/22/2016
Location
Boston, MA US
opyguy 5/9/2020 2:30pm
5/9/2020 2:30pm
Dmilkman589 wrote:
Well the stock 250sx is an S-1 so...
digger wrote:
You're right they changed to an s-4 needle jet in 2019. That rich 43-71 needle was a shot at a band aid fix. Instead of replacing...
You're right they changed to an s-4 needle jet in 2019. That rich 43-71 needle was a shot at a band aid fix. Instead of replacing the S-1 for the for the richer S-4 and leaner 42-75 needle they tried to just use a richer jet needle. KTM will never replace the most expensive problem, which is the 4.0 slide.
250sx has always used s-1 needle jet
Biggest change from 18 to 19 was the needle
43-73 to 43-71 or 72
1
digger
Profile picture for user digger
Posts
801
Joined
4/1/2008
Location
Upstate, NY US
digger 5/9/2020 2:50pm
5/9/2020 2:50pm
opyguy wrote:
250sx has always used s-1 needle jet
Biggest change from 18 to 19 was the needle
43-73 to 43-71 or 72
They must have changed it in the xc/xc-w line then. I know I have worked on some that came from the factory with an s-4 in them. I think the 125's may have even come with an s-7. Either way the richer jet needle is a band aid fix for the leaner s-1.
1
AJ565
Profile picture for user AJ565
Posts
2321
Joined
3/12/2012
Location
San Antonio, TX US
AJ565 5/9/2020 8:09pm
5/9/2020 8:09pm
opyguy wrote:
250sx has always used s-1 needle jet
Biggest change from 18 to 19 was the needle
43-73 to 43-71 or 72
digger wrote:
They must have changed it in the xc/xc-w line then. I know I have worked on some that came from the factory with an s-4 in...
They must have changed it in the xc/xc-w line then. I know I have worked on some that came from the factory with an s-4 in them. I think the 125's may have even come with an s-7. Either way the richer jet needle is a band aid fix for the leaner s-1.
Yeah it was the XC line that came with it.
1
opyguy
Profile picture for user opyguy
Posts
586
Joined
8/22/2016
Location
Boston, MA US
opyguy 5/10/2020 6:25am
5/10/2020 6:25am
opyguy wrote:
250sx has always used s-1 needle jet
Biggest change from 18 to 19 was the needle
43-73 to 43-71 or 72
digger wrote:
They must have changed it in the xc/xc-w line then. I know I have worked on some that came from the factory with an s-4 in...
They must have changed it in the xc/xc-w line then. I know I have worked on some that came from the factory with an s-4 in them. I think the 125's may have even come with an s-7. Either way the richer jet needle is a band aid fix for the leaner s-1.
Digger, try the17-62 needle from rm 125’s with the s1, really makes s huge difference.
riv187
Profile picture for user riv187
Posts
545
Joined
2/1/2015
Location
Lakeland, FL US
riv187 5/10/2020 8:24am
5/10/2020 8:24am
OK, I'e been out of touch with my 17 TC250 and 18 TC125 for a year. I got the new Dirtbike magazine and they praised the 250 and 125s for having spot on jetting.

I'm at 200 ft and often humid Florida and often sand.

Last numbers I had in my 250, with stock pipe,long PC Silencer,opened up airbox. Red PV spring 2 turns in.Aftermarket reeds and sanded reed cage flat.
MJ 470,
PJ 32.5,
slide 5.5sh I cut,
needle 42-75on 4th clip,
S-4 jet,
2 turns out on AS.
60-1 mix of 93ctane.

The 125,,Buds pipe and shorty silencer,,3 turns in on stock PV spring,opened airbox. Vforce
MJ 470 with a power jet to fatten up top end. 1-2 turns out.
PJ 32.5
Slide 5.5sh I cut.
needle 42-75 top clip
S-7
didn't record exact AS,,but 1- 1.5 out by memory
40-1 110 race gas

Both my bikes ran well ......What is different on the 2020s? What slides and combo they use for jets>is it better should I change something ????
Thanks


digger
Profile picture for user digger
Posts
801
Joined
4/1/2008
Location
Upstate, NY US
digger 5/10/2020 10:34am
5/10/2020 10:34am
opyguy wrote:
Digger, try the17-62 needle from rm 125’s with the s1, really makes s huge difference.
I have had one for a couple of months now, but I haven't had anything to really test it on. I've been messing around with a 36-39 oval bore Keihin STIC setup that I really like.
ar15
Profile picture for user ar15
Posts
62
Joined
8/31/2020
Location
NL
ar15 8/31/2020 9:11am
8/31/2020 9:11am
ron36 wrote:
Is there a gas slide between 4.0 and 5.75? I am afraid that the 5.75 of the kawasaki is too lean in the Netherlands in the...
Is there a gas slide between 4.0 and 5.75?
I am afraid that the 5.75 of the kawasaki is too lean in the Netherlands in the sand.
AJ565 wrote:
Yes there is, but the slide only is off idle to 1/4 throttle then tappers off to 1/2 throttle. In sand you really need bigger main...
Yes there is, but the slide only is off idle to 1/4 throttle then tappers off to 1/2 throttle. In sand you really need bigger main jetting.
What jet/slide/needle setup do you recommend to start from for riding in (deep) sand like we have over here (sea level, 2018 SX250, standard pipe and reeds).

Thx in advance
Fred
AJ565
Profile picture for user AJ565
Posts
2321
Joined
3/12/2012
Location
San Antonio, TX US
AJ565 8/31/2020 6:18pm
8/31/2020 6:18pm
ron36 wrote:
Is there a gas slide between 4.0 and 5.75? I am afraid that the 5.75 of the kawasaki is too lean in the Netherlands in the...
Is there a gas slide between 4.0 and 5.75?
I am afraid that the 5.75 of the kawasaki is too lean in the Netherlands in the sand.
AJ565 wrote:
Yes there is, but the slide only is off idle to 1/4 throttle then tappers off to 1/2 throttle. In sand you really need bigger main...
Yes there is, but the slide only is off idle to 1/4 throttle then tappers off to 1/2 throttle. In sand you really need bigger main jetting.
ar15 wrote:
What jet/slide/needle setup do you recommend to start from for riding in (deep) sand like we have over here (sea level, 2018 SX250, standard pipe and...
What jet/slide/needle setup do you recommend to start from for riding in (deep) sand like we have over here (sea level, 2018 SX250, standard pipe and reeds).

Thx in advance
Fred
I’ve been running in the sand for a few weeks now with the jetting laid out in this thread.

https://m.vitalmx.com/forums/Tech-Help-Race-Shop,42/KTM-HUS-125-150-250…
Ryno777
Profile picture for user Ryno777
Posts
47
Joined
9/6/2013
Location
ZA
Ryno777 1/28/2023 1:36am
1/28/2023 1:36am

Hey guys, just wanted to say a huge thanks to all of you. Got a wealth of info here. Picked up a 2018 KTM 250 SX (Which i googled and led me here), bike had only 3 hrs on. First ride I experienced what everyone here complains about which started the search. Found AJs specs there on the second comment and never looked back. 

Went with the 5.5 KX125 Slide, S4 needle jet, 42-75 needle, 460 Main and 32.5 Pilot. Did the JD jet block gasket for good measure. Dropped 1 tooth on the rear sprocket to 49. PV 1/4 In from stock. Added an fmf factory fatty for a bit more top end rpm and went with a long fmf 2.1 silencer (Not the shorty based on the issues I read with the R302 shorty vs the 302). I run 60:1 with pump gas here its 95 octane, in the Middle East and Maxima Formula K2.20230123 102214.jpg?VersionId=JvPl0NjIxK61DmVNGe

 

Bike Rips, I love it. Just again a big thank you to AJ and everyone. would never have found these settings on my own. Love it so much I sold my 2023 350 SXF and now use this only. 

 

AJ565
Profile picture for user AJ565
Posts
2321
Joined
3/12/2012
Location
San Antonio, TX US
AJ565 1/28/2023 12:57pm
1/28/2023 12:57pm

That’s a pretty lean main jet for those settings. With the 5.5 you should be at least a 490. 500 would be better. These bikes love big mains. I was seeing almost 2mph more between the 490 and 500 in the same section of track with the extra over rev from having more fuel. 

Ryno777
Profile picture for user Ryno777
Posts
47
Joined
9/6/2013
Location
ZA
Ryno777 1/28/2023 8:14pm
1/28/2023 8:14pm
AJ565 wrote:
That’s a pretty lean main jet for those settings. With the 5.5 you should be at least a 490. 500 would be better. These bikes love...

That’s a pretty lean main jet for those settings. With the 5.5 you should be at least a 490. 500 would be better. These bikes love big mains. I was seeing almost 2mph more between the 490 and 500 in the same section of track with the extra over rev from having more fuel. 

Thanks AJ for the reply. Sure I will bump up the mainjet to 490 as a start and see. I am riding in the UAE so Sea Level and coldest temp is 75 and summer over 100 so expecting to drop down again when the temps start creeping up but will drop a 490 in as a base and work from there. Sea level at 75 do you reckon the 32.5 pilot sounds correct. Bike is crisp in my opinion. 

Pit Row

See All »
AJ565
Profile picture for user AJ565
Posts
2321
Joined
3/12/2012
Location
San Antonio, TX US
AJ565 1/29/2023 7:36am
1/29/2023 7:36am
Ryno777 wrote:
Thanks AJ for the reply. Sure I will bump up the mainjet to 490 as a start and see. I am riding in the UAE so...

Thanks AJ for the reply. Sure I will bump up the mainjet to 490 as a start and see. I am riding in the UAE so Sea Level and coldest temp is 75 and summer over 100 so expecting to drop down again when the temps start creeping up but will drop a 490 in as a base and work from there. Sea level at 75 do you reckon the 32.5 pilot sounds correct. Bike is crisp in my opinion. 

I’m basically at sea level where I’m at and ride on 100+ days with the 32.5 and a 500 main. When it’s below 40° I do have to bump up to a 35 pilot and move one clip on the needle or it’s on the lean side. 

Ryno777
Profile picture for user Ryno777
Posts
47
Joined
9/6/2013
Location
ZA
Ryno777 1/29/2023 7:55am
1/29/2023 7:55am
Ryno777 wrote:
Thanks AJ for the reply. Sure I will bump up the mainjet to 490 as a start and see. I am riding in the UAE so...

Thanks AJ for the reply. Sure I will bump up the mainjet to 490 as a start and see. I am riding in the UAE so Sea Level and coldest temp is 75 and summer over 100 so expecting to drop down again when the temps start creeping up but will drop a 490 in as a base and work from there. Sea level at 75 do you reckon the 32.5 pilot sounds correct. Bike is crisp in my opinion. 

AJ565 wrote:
I’m basically at sea level where I’m at and ride on 100+ days with the 32.5 and a 500 main. When it’s below 40° I do...

I’m basically at sea level where I’m at and ride on 100+ days with the 32.5 and a 500 main. When it’s below 40° I do have to bump up to a 35 pilot and move one clip on the needle or it’s on the lean side. 

Great to know Thank you. I should never get near 40⁰ so thats perfect. 500 Main with the 32.5 Pilot for the next test it is. Appreciate all the replies on such an old forum. Glad I didnt give up on the Mikuni. 

ar15
Profile picture for user ar15
Posts
62
Joined
8/31/2020
Location
NL
ar15 1/29/2023 10:49am
1/29/2023 10:49am

FYI: I use this jetting table. I put it together using all the info that I found on this topic and some riding over the last year.

SX250 Mikuni Jetting

 

ar15
Profile picture for user ar15
Posts
62
Joined
8/31/2020
Location
NL
ar15 1/29/2023 10:51am
1/29/2023 10:51am

Now with complete table (top lines were missing)...

SX250 Mikuni Jetting 0

 

Ryno777
Profile picture for user Ryno777
Posts
47
Joined
9/6/2013
Location
ZA
Ryno777 2/1/2023 9:16pm
2/1/2023 9:16pm
ar15 wrote:
Now with complete table (top lines were missing)...  

Now with complete table (top lines were missing)...

SX250 Mikuni Jetting 0

 

That table is awesome, Thanks so much 

milošfusek
Profile picture for user milošfusek
Posts
9
Joined
3/4/2023
Location
Valašská Bystřice CZ
milošfusek 3/14/2023 12:52pm
3/14/2023 12:52pm

Please jetting for ktm sx 250 2019?
I am Czech Republic
550-700 meters above sea level
Temperature 25-30°C.
Thanks

AJ565
Profile picture for user AJ565
Posts
2321
Joined
3/12/2012
Location
San Antonio, TX US
AJ565 3/14/2023 6:26pm
3/14/2023 6:26pm
milošfusek wrote:

Please jetting for ktm sx 250 2019?
I am Czech Republic
550-700 meters above sea level
Temperature 25-30°C.
Thanks

It’s been in both threads you posted on. 
 

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

1
milošfusek
Profile picture for user milošfusek
Posts
9
Joined
3/4/2023
Location
Valašská Bystřice CZ
milošfusek 3/15/2023 2:10pm
3/15/2023 2:10pm
milošfusek wrote:

Please jetting for ktm sx 250 2019?
I am Czech Republic
550-700 meters above sea level
Temperature 25-30°C.
Thanks

AJ565 wrote:
It’s been in both threads you posted on.    Main jet 500 Pilot jet 32.5 Slide 5.75 (Kawasaki part#16025-0003) Needle 43-75 (KTM part #55431134400) Clip position...

It’s been in both threads you posted on. 
 

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

I have 470 main jet. It is problem?

milošfusek
Profile picture for user milošfusek
Posts
9
Joined
3/4/2023
Location
Valašská Bystřice CZ
milošfusek 3/17/2023 3:03am
3/17/2023 3:03am

Please Suzuki needle 16-72 for needle jet S4 or S1? 

AJ565
Profile picture for user AJ565
Posts
2321
Joined
3/12/2012
Location
San Antonio, TX US
AJ565 3/17/2023 5:28am
3/17/2023 5:28am

A 470 main jet is too lean for this setup. A 16-72 is the wrong needle for this setup. All of the parts numbers I listed are what’s needed for the setup and has been tested to work together properly so basically it’s an all or none kinda deal to work right. 

1
milošfusek
Profile picture for user milošfusek
Posts
9
Joined
3/4/2023
Location
Valašská Bystřice CZ
milošfusek 3/19/2023 11:54am
3/19/2023 11:54am

Is slide 5.5 the problem? My dealer only has 5.5 and 6.

5.75 out of stock.

AJ565
Profile picture for user AJ565
Posts
2321
Joined
3/12/2012
Location
San Antonio, TX US
AJ565 3/19/2023 3:26pm
3/19/2023 3:26pm

No you can use the 5.5. It might be a touch richer, but I’ve tested that slide too and had good luck with it. Also order needle 42-75 (Yamaha part #284-14116-H5-00) and start on the second clip and the air screw around 1 3/4 turns out. You might need to try both needles and see what one works best for you. 

1

Post a reply to: 2018 ktm 250sx jetting and FWW