2019 250XC Keihin Conversion

Hcallz5
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Hey there I've got a 2022 150SX that I did the Kiehin conversion on, runs great with the Sudco CCL needle. Going to pick up a 19' 250XC that I want to do the same thing with. 

 

Just wondering would I go leaner on the jetting for the 250 vs the 150? Tough part is I ride from 4500' to 9500' depending on the weekend so I need to find a good starting point. Doesn't need to be perfect or anything. Does anyone have any other needles that they have good luck with for enduro/single track with the occasional WOT area? 

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opyguy
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8/19/2025 7:18pm Edited Date/Time 8/19/2025 7:18pm

40 pilot

NECJ 4th clip down

175 main

Sea level 250 SX runs great was a little lean in the  3rd clip
 

Hcallz5
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8/19/2025 9:56pm

Sweet I may still have an NECJ kicking around in my brass bin from when I had a 200. I will have to give that go thanks for the input! 

sandman768
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8/20/2025 4:43am

Wonder if that necj needle would work on my 93 CR125 with the original PJ ? Waiting for Digger to chime in…

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digger
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8/23/2025 8:29am

The XC 250's usually uses a different setup than the SX. I would start out with an NECW needle in clip #3, 40/38 pilot, and a main around 162/160 for those elevations. 

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The Shop

digger
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8/23/2025 8:36am
sandman768 wrote:

Wonder if that necj needle would work on my 93 CR125 with the original PJ ? Waiting for Digger to chime in…

Those PJ carbs had a funky pilot circuit, and I never really messed around with them too much, so I don't have very good info on them. I do know, in a PWK, that needle would more than likely be too lean to use in the cr125.

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opyguy
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8/23/2025 11:44am
digger wrote:
The XC 250's usually uses a different setup than the SX. I would start out with an NECW needle in clip #3, 40/38 pilot, and a...

The XC 250's usually uses a different setup than the SX. I would start out with an NECW needle in clip #3, 40/38 pilot, and a main around 162/160 for those elevations. 

Gonna try the N3Wk in the sx

Any thoughts vs NECJ?

Sea level 70-85

Thx

digger
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8/23/2025 1:34pm
opyguy wrote:

Gonna try the N3Wk in the sx

Any thoughts vs NECJ?

Sea level 70-85

Thx

I like that series needle, but I don't use them much. They are very similar to the NExx series needles, but they rev, go thru the power range quicker than The NExx needles. It's not so much that they have a bigger hit, they just rev quicker. They are a fun series needle though. 

That K starting diameter is right on the edge of being lean. See if you can find an N3WJ or N3YJ, sold under a Suzuki part#, I think it will be more versatile than the K. 

As far as jetting goes, it should be an almost direct replacement for the NECJ, put the N3WK in clip #4 and leave the pilot and main as you have them now.

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Hcallz5
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8/23/2025 2:01pm

Yeah when I had the NECJ in my 200 it would rev super quick and kinda fall flat on the top. It was super fun under half throttle though. 

On the 250 I'll test out the NECW like you said but I'd also like to try the CCL and N3EW they seem popular as well. Tough to judge power characteristics without testing I guess. Thanks for your input as always digger! 🤙

digger
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8/23/2025 2:57pm
Hcallz5 wrote:
Yeah when I had the NECJ in my 200 it would rev super quick and kinda fall flat on the top. It was super fun under...

Yeah when I had the NECJ in my 200 it would rev super quick and kinda fall flat on the top. It was super fun under half throttle though. 

On the 250 I'll test out the NECW like you said but I'd also like to try the CCL and N3EW they seem popular as well. Tough to judge power characteristics without testing I guess. Thanks for your input as always digger! 🤙

You don't want the CCL in the 250, it's too rich. If you want to try a single taper needle, try a CEJ or CEK.  As far as the duel tapers go, start out with and N3CW or NHYW. 

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sandman768
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8/24/2025 5:02am
digger wrote:
Those PJ carbs had a funky pilot circuit, and I never really messed around with them too much, so I don't have very good info on...

Those PJ carbs had a funky pilot circuit, and I never really messed around with them too much, so I don't have very good info on them. I do know, in a PWK, that needle would more than likely be too lean to use in the cr125.

Thanks…

YZed250
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8/25/2025 11:53am

I'm assuming it's a used bike?
Those last year carb XCs and TXs are very hard to find in good used condition ... they seem to attract riders that put tons of hours on and rarely perform basic maintenance. So a lot of the bikes have air leaks, broken reeds, low compression, blown out packing etc etc!

HIGHLY recommend thorough service before making mods/replacing carbs. I had good success with the Mikuni on my 250sx ... I'd also suggest trying the stock carb before junking it. 

 

romain524
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8/25/2025 2:35pm
Hcallz5 wrote:
Yeah when I had the NECJ in my 200 it would rev super quick and kinda fall flat on the top. It was super fun under...

Yeah when I had the NECJ in my 200 it would rev super quick and kinda fall flat on the top. It was super fun under half throttle though. 

On the 250 I'll test out the NECW like you said but I'd also like to try the CCL and N3EW they seem popular as well. Tough to judge power characteristics without testing I guess. Thanks for your input as always digger! 🤙

digger wrote:
You don't want the CCL in the 250, it's too rich. If you want to try a single taper needle, try a CEJ or CEK.  As...

You don't want the CCL in the 250, it's too rich. If you want to try a single taper needle, try a CEJ or CEK.  As far as the duel tapers go, start out with and N3CW or NHYW. 

Does the N3CW work great for both PWK 36 and 38? I’m assuming the OP got a 36 from a previous year ktm 250/300.

digger
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8/26/2025 12:14am
romain524 wrote:

Does the N3CW work great for both PWK 36 and 38? I’m assuming the OP got a 36 from a previous year ktm 250/300.

It can, but it will require a different size main jets between the 38 and 36 carbs, but the needle and pilot should remain the same. The 38mm carb will need a richer main, 1-2 sizes, than the 36mm carb.

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Hcallz5
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8/26/2025 9:52am
romain524 wrote:

Does the N3CW work great for both PWK 36 and 38? I’m assuming the OP got a 36 from a previous year ktm 250/300.

I've got a couple 36's and 38's that I've bought when I find a good deal, it seems like spare Keihin carbs are getting harder to find and people are charging more for them. I had a 2019 TX300 with the TMX38 and it was a nightmare, I think now it seems like guys have figured out what it takes to make them work well but I haven't really paid attention. 

Thanks for all the help digger, I wish I had all your needle knowledge! 😂

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