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What’s your elevation and jetting on the 250sx?
always curious on keihin jetting
im at 42/Necj /175
thx
From memory, I think I was 48/175/N3EJ-2 with a 6.5 slide running 40:1 with avgas.
What jetting setup are you running on the mikunis, I tried almost everything. I tried a JD kit and it was an improvement but the Keihin worked better everywhere for me. On my 250xc I’m running the sx ignition, fmf fatty and 2.1 shorty, rk tech head, V-force V4R reeds and the red power valve spring. On my 300xc I’m running the same setup except a PC exhaust system. It’s not a lot of mods but it helps tremendously with overall power and over-rev.
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Start on page-1 of this thread and go from there, lol. Here is where I ultimately ended up, all with straight avgas at 38:1 with Motul 800:
250:
PJ 37.5
Main 500
Needle 42-75, clip 2
Needle Jet S4
Slide 5.75
AS 1.5-1.75
300:
PJ 35
Main 500
Needle 43-75, clip 2
Needle Jet S4
Slide 5.75
AS 1.5-1.75
This is my bike with PC pipe and 304 silencer at the time running u4.4 at 60:1 with just the jetting from page 1. 2018 250sx
Im running the same set up as you from page 1. just move the needle up to #3 worked on mine for both my 250 and 125 they both responded well too the change on the AVgas, and is also working well with 2:1 91 Pump/ U4.4 36:1 Motorex
Good deal, I just moved mine to position 3 and i am testing tomorrow! Will also try to mix more oil and see how she likes it.
I’m still having the bog, it’s in the top end, PV at 1.75 in from all the way out, Air screw about 1.5. Is it possible I have a cracked reed? That’s all I can think as of now.
Ran c12 through it and the thing ran like a raped ape hahahaa. Avgas was the culprit for me. RIP my wallet now
Hi, do you have new jetting information for 300sx. I also have a 300 but I have difficulty adjusting it correctly, I drive it like a 125, in deep sand.
450
32,5
44-75 2nd position
A/S:2
Just what’s on the first page. You need the slide to make the jetting work, the stock one is too rich and there is no getting around that.
You can cut it 50/50 with pump gas to help cut the cost.
Yup, you need the slide like AJ said. Look a few posts above for what I am running in my 300. I am not riding deep sand but I feel like this jetting is on the "safe" side and would at least be a very close starting point to get you going. I'd be afraid to run a 450 main in sand !
300:
PJ 35
Main 500
Needle 43-75, clip 2
Needle Jet S4
Slide 5.75
AS 1.5 - 1.75
Motul 800 at 38:1 with 100LL AvGas
Im going to test, I have all of them and I also ride motul 800 39:1 and avgas100ll.
i test this in few days and go back to you.
thanks guys.
wich powervalve spring ?
Digger,
I was trying to find the post about the notch in the slide. I have a 2018 and a 2019 ktm 150 sx that I am preparing to file the slides notchs. What depth do I go to?
I am currently running
Slide #5
Main 490
Pilot 30- had a 35 but it was too rich and I have 32.5 and 27.5 coming to try
needle- 42-74
JD gasket
Bike runs better with these settings but want to clean up the idle.
Ricky, I use a 5/32 or 4mm chainsaw file, and file down about 3mm in depth. It's not super critical, like filing the other side of the slide is. There is a pic on page 5 in this thread of a slide that I cut and notched that will give you and idea of what I'm doing, and how deep to go with the notch.
Pit Row
Hi guys, I’m back with your jetting.I don't have the needle so I imagine it should still work better with it.. actually the bike works well even with the wrong needle (currently 44-75 2nd clip). I order and install the right needle and go. I found a needle chart (in French because I'm French 🤪)
OK, so it's running good? Yeah 44-75 essentially has grooves cut 1 whole clip richer than 42-75. So, 44-75(2) basically equals 42-75(3). This might not be a bad thing since you're in sand. But, like you said, I would still try 43-75(2) just to be sure and compare.
Hi, I’ve bought a ktm 150 sx 2017 and I’m struggling to get the mikuni carb right. I’ve changed the jet block gasket from JD.
I’ve ordered all the parts in your suggested carb settings for the 17+ 150 hoping to solve the bike it bogs in 1st & 2nd as if it colds when it’s not then picks up. It’s not running crisp like a two stroke should it’s not screaming like a 150 should.
pump gas 98 @ 40:1 2t motorex oil
UK
2022 125SX
MJ 540
PJ 32.5
AS 1.50
slide 5.0 from JD Jetting
Needle 42-74 on the 3rd clip (Yamaha 284-14116-H4-00)
Needle jet S4 (KTM part #55431021400)
PV 1.5 turns in from all the way out.
Fuel mix 91pump/U4.4 2:1 Motorex 36:1
Warning the bike will run very fast on this jet and fuel mix but will run hot. just cracked a head today at ACP. both the piston top and plug were chalk white. very lean. I had an exhaust o ring fail also that may have pushed the lean condition.
after the rebuild im considering
MJ 540
PJ 35
AS 1.0
slide 5.0 from JD Jetting
Needle 42-74 on the 4th clip (Yamaha 284-14116-H4-00)
Needle jet S4 (KTM part #55431021400)
PV 1.5 turns in from all the way out.
Fuel mix 91pump/U4.4 2:1 Motorex 36:1
is there another needle jet that can open the fuel up 5%, maybe the stock S1. Am i correct in thinking the needle jet will affect my main jet. Im up to a 540 from the stock 500 and its still lean. I think there is one bigger main jet i can get, but is there diminishing returns on the bigger jets. the bike too rich with this fuel mix stock and too lean now. I just need a little more fuel.
The S1 is leaner than the S4. You want the S7 to make it richer. Also, on the 2022 bikes I ended up on a 37.5 pilot running AvGas which is non-Oxy. You probably need to go richer on the pilot and/or needle straight section (like to a 42-72 or so) as well. Ultimately you'll need to find the right combo of Needle-jet and Jet-needle to work correctly across the whole range.
Thank you for your input. I have new parts on order and will continue testing.
Hi from Argentina! Ive read the 35 Pages of this Amazing topic. Somebody knows what needle jet ( S1 or S4) comes in 2017 150sx from factory and where is located in carb ? .
Planing go with this
Sea level , between 50°F and 77°F most of the year. running Pump gas. Shell Vpower.
Begginer 180lbs without gear.
(40/50°F Winter sand/dunes conditions)*
MJ 500 (540)*
PJ 35 (37.5)*
Slide #5 JD jetting without notch
S4
Needle 42-74 2 pos (3 pos) *
I hope You can confirm if im in the right direction with this. Thank You all, for be SO active in this topic.
That sounds like some good starting points for you.
Make sure you check the float height also to 8 - 9mm.
From the manual, your bike has the S-1:
To Remove the needle-Jet, remove slide assembly, remove carb from bike, remove float bowl and float, remove main jet, and then remove the 8mm brass nut under main jet (Main jet holder). The needle-Jet is behind that. If it does not fall out the bottom easy, use a tool and push down gently from the top of the carb and it should fall out.
When you have all this apart, you should remove the 2-torx screws and replace the jet block gasket also to make sure that is fresh and sealed well.
https://jdjetting.com/product/jdmk05-mikuni-tmx-jet-block-kit/
Hi,
Tried to find information in this huge thread but think I came up short. I have a Husky TC 125 2020 that is now equipped with KTM complete new 150 kit. The call it factory but I believe it is bog standard 150SX kit or?
Now my real question, the former owner had the TMX38 carb bored out so now I measured it to 40mm, how does this affect jetting? Bike is really bad on low to maybe’s mid throttle with 4.0 slide and jetting according 150 manual. I would say uneven and sputters.
Live in sweden so spring for us now is 40-50F, sea lvl. Have JD gasket. Float looks ok at 60 degrees. Just got a 5.0 slide installed. Have standard needles/jets and JD kit needles/jets for 125. Do not know if the are the same in JD 150 kit. To make matters even worse I will run it mostly on sand MX tracks but I’m only dreaming of wide open, it does not happen in real life. So any jetting advice would be much appreciated.
/Robert
Yeah, still struggling so I will answer myself
Tried to file down my 4.0 slide to a leaner but it looks more like a 5.0 so far. Still used it last time and here are my findings. Rather cold around 9 degrees Celsius cooling down towards 6c later on. Riding rather heavy sand mx-track. Started with 520/35 and 42-71 on 3rd. Sounds and goes like a lawnmower down low
thought it went better when adjusting airscrew out 1 1/2 turn so went down to a 30 pilot and put airscrew back at 1 2/3.
Didn’t really notice any improvement so moved clip up to second. Maybe a slight improvement but still rather bad when trying to maintain a steady (low) trottle. Should I continue moving to first clip or find a leaner needle? A bit unsure to make it leaner since since riding sand and cold temperatures? Could my drilled out carb (40mm) cause me all this headache?
Time for the ole DIY larger slide notch.
My motor was full of oil where the connection pipe/silencer and this is my spark with just two hrs
any advice please 🙏🏼
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