KTM 250 SX Carb Swap

K22
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K22 10/28/2014 5:24pm
10/28/2014 5:24pm
What jetting do you think i should run for 40 degree celcius temps at about 300m above sea level?
Digger29
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Digger29 10/29/2014 5:48am
10/29/2014 5:48am
For strictly MX I'd start with a 42 pilot, RM250 NECJ needle on the 3rd setting and a 175 main jet.
lumpy790
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lumpy790 10/29/2014 7:10am
10/29/2014 7:10am
why not just bore the 36 to a 38?
97nismo
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97nismo 10/29/2014 8:37am
10/29/2014 8:37am
lumpy790 wrote:
why not just bore the 36 to a 38?
If you can find a reputable place to do it for cheaper then buying a 38mm carb then go for it. I looked around and after paying for the boring and shipping both ways, it was cheaper to buy a new carb. Plus I had zero down time, which was important because I was in the middle of a race season.

The Shop

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malburg114
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malburg114 11/3/2014 12:41pm
11/3/2014 12:41pm
Digger29 wrote:
For strictly MX I'd start with a 42 pilot, RM250 NECJ needle on the 3rd setting and a 175 main jet.
What about for desert racing in Las Vegas, NV (Jean, Boulder City) on a 2013 KTM 300 XCW??
Digger29
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Digger29 11/3/2014 3:03pm
11/3/2014 3:03pm
Digger29 wrote:
For strictly MX I'd start with a 42 pilot, RM250 NECJ needle on the 3rd setting and a 175 main jet.
malburg114 wrote:
What about for desert racing in Las Vegas, NV (Jean, Boulder City) on a 2013 KTM 300 XCW??
If you're on the gas a ton and I'd think you are if you're racing desert I'd say you could even go with a bigger main say178-180ish
Skali
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Skali 11/13/2014 2:07pm
11/13/2014 2:07pm
What is the difference between throttle valve 6.5 and 7 in Keihin PWK 38S?
digger
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digger 11/13/2014 5:07pm
11/13/2014 5:07pm
Skali wrote:
What is the difference between throttle valve 6.5 and 7 in Keihin PWK 38S?
1/2 mm, The 7.0 slide is leaner than the 6.5. The 7.0 will provide crisper throttle response up tp about 1/2 throttle over 6.5. Where as the 6.5 slide may provide a little more torque up to the same 1/2 throttle.
kylant
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kylant 4/9/2015 6:40pm
4/9/2015 6:40pm Edited Date/Time 4/9/2015 6:43pm
Digger29 wrote:
That's definitely the right carb. Keep the 6.5 slide from your stock 36 and install that in the 38 carb. Also don't forget to get the...
That's definitely the right carb. Keep the 6.5 slide from your stock 36 and install that in the 38 carb. Also don't forget to get the Suzuki NECJ needle and put a 175 main jet in it and you'll be good to go.
what elevation are you running this jetting at?

also what is the correct part number for the vforce 4 for the 2014 250 sx?

thx
gameover
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gameover 5/15/2015 12:37pm
5/15/2015 12:37pm
http://www.magicracing.com/KTM-CARBUR-KEIHIN-PWK-38S-AG-09_p_122176.html

$269.87 shipped (this one has the 7 slide)

http://www.magicracing.com/KTM-CARB-KEIH-PWK-38S-AG-BC0-11_p_122177.html

$326.42 shipped (this one has the the 6.5 slide)

Will I ever use the 7 slide on a 2015 tc250?

The question stems from the thought of which market, 125cc or 150cc bikes, will i have a higher probability of selling my 36mm carb to.
hoova
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hoova 5/16/2015 4:51am
5/16/2015 4:51am
Has anyone taken their stock 36mm carb to a machine shop and had it bored out to 38mm or oval bored 36/339mm? It seems like a much cheaper option
MxKing809
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MxKing809 5/16/2015 6:15am
5/16/2015 6:15am
hoova wrote:
Has anyone taken their stock 36mm carb to a machine shop and had it bored out to 38mm or oval bored 36/339mm? It seems like a...
Has anyone taken their stock 36mm carb to a machine shop and had it bored out to 38mm or oval bored 36/339mm? It seems like a much cheaper option
I had Dicks do that to my 200xc carb and it was a pain in the ass to jet. I would rather have a standard bore carb and not try to jet for two different profiles
MxKing809
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MxKing809 5/16/2015 6:16am
5/16/2015 6:16am
And I finally got a 38mm airstriker..... but it's on my CR125 Evil
kylant
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kylant 5/17/2015 4:41pm
5/17/2015 4:41pm
what kind of pipe and silencer combo seems to work the best with this set-up?
gameover
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gameover 5/20/2015 8:06am
5/20/2015 8:06am
I am very confused. In pursuit of a 38mm carburetor , I just ordered:

50331101544 CARBUR. KEIHIN PWK 38S AG 09 for $345.92 is the carburetor for a 2015 Husqvarna TC125

However,

51531001244 CARBUR. KEIHIN PWK 38S AG | 09 for 263.87 is the carburetor for a 2009 KTM 150SX

Its almost a $90 difference.

The only difference I can tell is :54831029000 THROTTLE CALBE HOLDER M6X0,75

Any insights?
digger
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digger 5/20/2015 8:39am
5/20/2015 8:39am Edited Date/Time 5/25/2015 5:59pm
The xxx1544 carb is physically the exact same as the xxx1244, with the only difference being that the xxx1244 has a 6.5 slide, where as the xxx1544 has a #7 slide. For use in your 250 I would prefer the #7 slide for all around use. the #7 slide will provide cleaner response down low, in about the first 40% of the throttle range. The 6.5 slide is very usable, but just not as clean, and may hit harder into the midrange depending on the jetting. That may be a good thing, if that's what you're looking for.

The only throttle cable holder that you do not want to use are the ones used in Yamaha YZ's. They use a spring loaded holder that should only be used in their slides. For some reason Yamaha slides are drilled different, hole for the needle jet, than all of the other OEM's. The spring loaded holder, holds the needle jet to tight in other OEM's slides and over time WILL cause the needle jet to break.
gameover
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gameover 5/25/2015 2:10pm
5/25/2015 2:10pm
Thanks digger! I ended up buying a 2015 tc250 carb for my tc250.
gameover
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gameover 6/5/2015 4:24pm
6/5/2015 4:24pm Edited Date/Time 6/5/2015 4:26pm
Ooooook. I got the 38mm carb from a 15 tc125 and installing it onto a 15 tc250. Leaving the 7 slide and porting over the 36mm jetting and 08 rm250 necj needle on 3rd clip.

Looks identically the same

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Madmax31
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Madmax31 6/6/2015 8:52am
6/6/2015 8:52am
Digger29 wrote:
Have you read the review's from the all of the guys who running the Smart Carb? I think I've read over 200+ pages and I don't...
Have you read the review's from the all of the guys who running the Smart Carb? I think I've read over 200+ pages and I don't think there is one guy that has his cast or billet Smart Carb working correctly. It appears to be a very flawed product. I'm all set with that. I'll stick with my perfectly jetting and starts on the first kick every time 38mm Keihin carb.
Did u ever try the dicks racing carb mod. Mxa loved it.
ratonmacias
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ratonmacias 6/9/2015 1:14pm
6/9/2015 1:14pm
If anybody is willing to sell a takeoff 36 mm keihin let me know.
ratonmacias
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ratonmacias 6/9/2015 1:15pm
6/9/2015 1:15pm
If anybody is willing to sell a takeoff 36 mm keihin let me know.
gameover
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gameover 6/9/2015 1:29pm
6/9/2015 1:29pm
ratonmacias wrote:
If anybody is willing to sell a takeoff 36 mm keihin let me know.
What are you looking to pay?
reded
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reded 6/10/2015 4:49am
6/10/2015 4:49am
ratonmacias wrote:
If anybody is willing to sell a takeoff 36 mm keihin let me know.
I've got one I'll sell ya. Looks like new with only 12 hrs of run time on it.
ratonmacias
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ratonmacias 6/11/2015 8:40pm
6/11/2015 8:40pm
I wouldnt like to put a price on your carb it would be better if you email me inganma@gmail and tell me what you expect to get for the carb. im putting it on my 04 cr 250.
kylant
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kylant 6/18/2015 6:51am
6/18/2015 6:51am
quick questions:

my 38mm carb will be here today. Do I just run the same jetting from my 36? I know to swap the 6.5 slide over, but what about the rest?

I am at 6300 ft elevation and the temps are about 75-80* now, virtually no humidity. I am running a 38p, NECJ clip #2, 158 main, and AS 1.5 out. Bike runs really good.

thanks
seth505
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seth505 6/18/2015 7:20am
6/18/2015 7:20am Edited Date/Time 6/18/2015 7:20am
kylant wrote:
quick questions: my 38mm carb will be here today. Do I just run the same jetting from my 36? I know to swap the 6.5 slide...
quick questions:

my 38mm carb will be here today. Do I just run the same jetting from my 36? I know to swap the 6.5 slide over, but what about the rest?

I am at 6300 ft elevation and the temps are about 75-80* now, virtually no humidity. I am running a 38p, NECJ clip #2, 158 main, and AS 1.5 out. Bike runs really good.

thanks
Yes, other than the slide, start off with the same jetting and fine tune if you really need to. Mine worked out by doing this, I think I ended up with the air screw slightly different.
gameover
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gameover 6/18/2015 7:36am
6/18/2015 7:36am
I left the slide that came with the 38mm carb and just moved over the jetting I had with the 36mm carb.

Havent been able to test it since im waiting on my suspension to het here.
digger
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digger 6/19/2015 6:43am
6/19/2015 6:43am Edited Date/Time 8/17/2015 6:42pm
gameover wrote:
I left the slide that came with the 38mm carb and just moved over the jetting I had with the 36mm carb. Havent been able to...
I left the slide that came with the 38mm carb and just moved over the jetting I had with the 36mm carb.

Havent been able to test it since im waiting on my suspension to het here.
Do yourself a favor and startout with a main jet 2 to 3 sizes larger than what you were using in the 36. The decrease in the velocity of the air that is drawn through the 38mm carb will require a larger main jet. You also may need to increase the pilot jet 1-2 sizes as well to startout with.
kylant
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kylant 6/20/2015 6:03am
6/20/2015 6:03am
gameover wrote:
I left the slide that came with the 38mm carb and just moved over the jetting I had with the 36mm carb. Havent been able to...
I left the slide that came with the 38mm carb and just moved over the jetting I had with the 36mm carb.

Havent been able to test it since im waiting on my suspension to het here.
digger wrote:
Do yourself a favor and startout with a main jet 2 to 3 sizes larger than what you were using in the 36. The decrease in...
Do yourself a favor and startout with a main jet 2 to 3 sizes larger than what you were using in the 36. The decrease in the velocity of the air that is drawn through the 38mm carb will require a larger main jet. You also may need to increase the pilot jet 1-2 sizes as well to startout with.
with this advice, do you suggest doing anything with the needle?

i was running a 40p, NECJ #3, 160 main, as 2 prior to swapping to the 38, NECJ#2, 158, but the air temps were a good 10* cooler. bike still ran good, but I think it was a little fat on the bottom.

sounds like maybe I should go back to the richer jetting for the 38 carb and see how she runs?!


oh and BTW, I got the carb listed for a 2014 150sx, and it came with a 7 slide instead of the 6.5 posted earlier. KTM must have made a change. I tried to get an earlier model carb, but this was the only one available without a long backorder
digger
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digger 6/21/2015 12:55pm
6/21/2015 12:55pm
gameover wrote:
I left the slide that came with the 38mm carb and just moved over the jetting I had with the 36mm carb. Havent been able to...
I left the slide that came with the 38mm carb and just moved over the jetting I had with the 36mm carb.

Havent been able to test it since im waiting on my suspension to het here.
digger wrote:
Do yourself a favor and startout with a main jet 2 to 3 sizes larger than what you were using in the 36. The decrease in...
Do yourself a favor and startout with a main jet 2 to 3 sizes larger than what you were using in the 36. The decrease in the velocity of the air that is drawn through the 38mm carb will require a larger main jet. You also may need to increase the pilot jet 1-2 sizes as well to startout with.
kylant wrote:
with this advice, do you suggest doing anything with the needle? i was running a 40p, NECJ #3, 160 main, as 2 prior to swapping to...
with this advice, do you suggest doing anything with the needle?

i was running a 40p, NECJ #3, 160 main, as 2 prior to swapping to the 38, NECJ#2, 158, but the air temps were a good 10* cooler. bike still ran good, but I think it was a little fat on the bottom.

sounds like maybe I should go back to the richer jetting for the 38 carb and see how she runs?!


oh and BTW, I got the carb listed for a 2014 150sx, and it came with a 7 slide instead of the 6.5 posted earlier. KTM must have made a change. I tried to get an earlier model carb, but this was the only one available without a long backorder
You've got the right carb with the right slide.

That NECJ needle is fine to start out with. Ideally you want to start out a little rich and work your way leaner, especially with the main jet. With that said, start out with the Needle in the #3 clip, with the 40 pilot and a 168 main and work your way leaner, if you need to.

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