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Discussion Starter #1
My friend and I just bought matching 2018 KTM 150SXs and they're amazing but the jetting is way off. Has anyone sorted this out already? Currently my bike is too rich. The top end seems pretty good but the bottom and mid are terrible. Here are the details:
Elevation: Less than 300ft above sea level
Temp: 0deg C to 8dec C (32 to 46deg F)
Fuel: 50:1
Current Jetting:
Main: 470
Needle: 42-74
Needle Clip Position: 3
Idle Jet: 35
Air screw: 2 turns out (Mine was 8.5 initially!)

Recommended Setting from KTM Manual for this temp/elevation:
Main: 490
Needle: 42-74
Needle Clip Position: 3
Idle Jet: 37.5
Air screw: 1.5 turns out

MXA did the following to the 2017 but it seems extreme and I'm not sure whether the 2018 will be identical.
Here’s what we ran in our 38mm TMX (stock settings in parentheses):
Main jet: 460 (470)
Pilot: 40 (45)
Needle: 44–74 (43–74)
Clip: 1st clip (3rd clip)
Air screw: 3 turns out (1-1/2 turns out)

Any recommendations?
 

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Dirt Wizard
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3,728 Posts
Welcome to the forum.
The mixture screw is behind the slide like most 2 strokes I gather? 8 1/2 turns out is ridiculously lean?
Usually 1-1/2 turns out is about right. I gather you would know 99% of the time out for lean when screw is behind the slide, in for lean when screw is engine side of the slide.

I haven't worked on enough 150's to know the perfect jet combinations unfortunately.
 

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Great question kakabeka. I have a 2018 150 sx and ride mostly in the woods and race gncc. I’ve got it dialed in now but it has been a huge problem and the settings that work are way off the stock settings. Can you tell me a bit more about the type of riding that you and your friend do? What level are you?
 

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Discussion Starter #5
So, I forgot I had posted this. I spent this season playing with different settings and have made little progress. We do woods riding and are solid intermediate level. The best setting I've found so far is as follows:

Elevation: Less than 300ft above sea level
Temp: 0deg C to 8dec C (32 to 46deg F)
Fuel: 40:1 (corrected this from initial after reading the manual - our dealer had told us 50:1)
Current Jetting:
Main: 470
Needle: 42-74
Needle Clip Position: 3
Idle Jet: 37.5
Air screw: 1.75 turns out

The top end seems great but the real issue is at 1/4 to 1/2 throttle.

My friend got the JD Jetting kit which has been even worse so far. He has emailed them recently and they advised him that they're sending a new kit since they have recently revised their 2018 kit. According the JD Jetting: "We have had an update to the kit . KTM actually changed the nozzles in the carbs and not even the tech manuals called it out. " Interestingly, the pilot and main seemed similar to KTM stock but JD had recommended the 32.5 idle jet and 450 main jet but their JD needle which is way different looking than stock.

KTM Expert - I'm going riding on Monday. If you send me the jetting that you'd recommend based on my riding level, I'll try it out. The weather is cooler - the high on Monday will be 41 deg F or 5 deg C. Any help would be greatly appreciated! It seems crazy to me that we'd have to go to a Lectron card or swap in the Keihin.'
 

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Full Throttle
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5,499 Posts
get the motor coming off idle fast but dont rev it over a 1/4 throttle when testing. lower the size of idle jet so it seems to over run your throttle blip, test with a more open air screw than what is recommended , lets say test with 2.5 turns out. have the needle in the middle for testing.

when you get that fast blip, turn your thoughts to how it revs and rides from 1/4 to 1/2 throttle , both blips and riding.
come back with what you deducted .




1 55431001244 CARBURETOR TMX38
1
462.06 €
3 55431051080 STARTING JET ''80''
0
13.50 €
3 55431051050 STARTING JET ''50''
0
13.50 €
4 55431021000 NEEDLE JET ''R-8''
0
12.96 €
4 55431021700 Needle jet S-7
0
12.96 €
4 55431021400 Needle jet S-4
0
12.96 €
4 55431021100 NEEDLE JET ''S-1''
0
12.96 €
5 52031137001 PVC-HOSE 3X5MM
0
1.64 €
5 31007007101 PVC-HOSE 4X6MM
0
3.21 €
6 55431245000 start piston
1
27.14 €
7 55431699000 SCREW PLUG CPL.
1
21.01 €
8 0014050163 HH COLLAR SCREW M 5X16 WS=6
3
1.98 €
9 55431017000 ADJUSTER & COMPRESSION SPRING
1
12.14 €
10 55431019000 Adjuster
1
10.78 €
11 55431034050 RING
1
3.96 €
12 55431009000 FLOAT & PIN
1
67.87 €
13 55431011000 FLOAT CHAMBER CPL.
1
107.21 €
14 55431030050 GUIDE HOLDER
1
13.50 €
15 55431027000 CARBURETTOR COVER
1
33.96 €
16 55431030000 SLIDING SPRING MIKUNI
1
8.12 €
17 55431034060 LOCK RING
1
2.59 €
18 55431020000 FLOAT NEEDLE CPL.
1
27.14 €
19 55431025000 screw carburator cover
2
4.77 €
20 55431029600 MAIN JET ''600''
0
8.05 €
20 55431029580 MAIN JET ''580''
0
8.05 €
20 55431029560 MAIN JET ''560''
0
8.05 €
20 55431029540 MAIN JET ''540''
0
8.05 €
20 55431029520 MAIN JET ''520''
0
8.05 €
20 55431029500 MAIN JET ''500''
0
8.05 €
20 55431029490 MAIN JET ''490''
0
8.05 €
20 55431029480 MAIN JET ''480''
0
8.05 €
20 55431029470 MAIN JET ''470''
0
8.05 €
20 55431029460 MAIN JET ''460''
0
8.05 €
20 55431029450 MAIN JET ''450''
0
8.05 €
20 55431029440 MAIN JET ''440''
0
8.05 €
20 55431029430 MAIN JET ''430''
0
8.05 €
20 55431029420 MAIN JET ''420''
0
8.05 €
20 55431029410 MAIN JET ''410''
0
8.05 €
20 55431029400 MAIN JET ''400''
0
8.05 €
20 55431029155 MAIN JET ''155''
0
8.05 €
20 55431029100 MAIN JET ''100''
0
8.05 €
21 55431007525 IDLING JET ''52.5''
0
10.78 €
21 55431007500 IDLING JET ''50''
0
10.78 €
21 55431007475 IDLING JET ''47.5''
0
10.78 €
21 55431007450 IDLING JET ''45''
0
10.78 €
21 55431007425 IDLING JET ''42.5''
0
10.78 €
21 55431007400 IDLING JET ''40''
0
10.78 €
21 55431007375 IDLING JET ''37.5''
0
10.78 €
21 55431007350 IDLING JET ''35''
0
10.78 €
21 55431007325 IDLING JET ''32.5''
0
10.78 €
21 55431007300 IDLING JET ''30''
0
10.78 €
21 55431007275 "Idle jet ""27,5"""
0
9.35 €
21 55431007250 "Idle jet ""25"""
0
9.35 €
21 55431007225 "Idle jet ""22,5"""
0
9.35 €
21 55431007175 IDLING JET ''17.5''
0
10.78 €
21 55431007150 IDLING JET ''15''
0
10.78 €
22 55431073000 distance holder
3
5.32 €
23 55431017010 COMPRESSION SPRING ADJUSTER
1
4.58 €
24 55431019010 compressing spring
1
5.32 €
25 55431012000 plate
2
2.67 €
26 55431010000 Holder
1
8.05 €
30 55431234500 JET NEEDLE ''6BFY44-76''
0
10.78 €
30 55431234400 JET NEEDLE ''6BFY44-75''
0
10.78 €
30 55431234300 JET NEEDLE ''6BFY44-74''
0
10.78 €
30 55431234200 JET NEEDLE ''6BFY44-73''
0
10.78 €
30 55431234100 JET NEEDLE ''6BFY44-72''
0
10.78 €
30 55431234000 JET NEEDLE ''6BFY44-71''
0
10.78 €
30 55431134500 JET NEEDLE ''6BFY43-76''
0
10.78 €
30 55431134400 JET NEEDLE ''6BFY43-75''
0
10.78 €
30 55431134300 JET NEEDLE ''6BFY43-74''
0
10.78 €
30 55431134200 JET NEEDLE ''6BFY43-73''
0
10.78 €
30 55431134100 JET NEEDLE ''6BFY43-72''
0
10.78 €
30 55431134000 JET NEEDLE ''6BFY43-71''
0
10.78 €
30 55431034500 JET NEEDLE ''6BFY42-76''
0
10.78 €
30 55431034400 JET NEEDLE ''6BFY42-75''
0
10.78 €
30 55431034300 JET NEEDLE ''6BFY42-74''
0
10.78 €
30 55431034200 JET NEEDLE ''6BFY42-73''
0
10.78 €
30 55431034100 JET NEEDLE ''6BFY42-72''
0
10.78 €
30 55431034000 JET NEEDLE ''6BFY42-71''
0
10.78 €
30 55431934000 JET NEEDLE ''6GAY69-74''
0
10.78 €
99 55431099000 Gasket set Mikuni
0
12.21 €
 

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Hi, When you choosing jetting settings for KTM you can ussualy go one up and one right in table.Here is picture of jetting settings of my '17 Sx 125,but i think that is same for "18 Sx 150(they have same carb Mikuni TMX 38).Right settings for your bike by KTM is in red box but i would go to the settings in black box.(if you plan to ride in winter you can go just one up and not right)
 

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Discussion Starter #10
Thanks for all the help everyone!

I followed the KTM recommendations for the weather on Monday which led me to the following settings (in red pen in attached photo):
Elevation: Less than 300ft above sea level
Temp: 3 deg C (37 deg F)
Fuel: 40:1 (corrected this from initial after reading the manual - our dealer had told us 50:1)
Jetting:
Main: 490
Needle: 42-74
Needle Clip Position: 3
Idle Jet: 37.5
Air screw: 1.5 turns out

We had both bikes (my friend's bike mentioned above) at these settings. Mine was ok in the upper-mid and top end but boggy in the bottom end. My buddy's was terrible until you got to the top end. I tried playing with the air screw but couldn't get that over-rev referred to by cors187. After watching that video, I'm going to try the recommendation of going up one and to the right one. That will change my idle jet to a 35, main jet to a 470 and air screw to 1.5 as indicated in blue in the attached photo. I hope he's right. It seems insane that you'd have to swap out the carb on a brand new bike.

On a related note, my buddy has the JD Kit which indicated that it was the same for the 2017 150 SX and the 2018 150 SX. He's since talked to the tech at JD who said they are working on a new kit as KTM changed the carb in 2018 without mentioning it in the technical specs so the kit by buddy got didn't work at all.
 

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The 150sx I have seen all have a Mikuni. Are you saying that KTM changed the model of Mikuni in them? The specs from 2017 - 2020 tells us the carbi is the same Mikuni 38mm TMX.
 
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