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No surprise here… Changed the jet block gasket while going through the carb to see what I have.
here is what is in the carb now. Note: it may or may not be Oem jetting as i just bought the bike used.
Main: 500
pilot: 35
air screw 1.75
Slide#4
needle: 43-71 2nd pos
i am assuming have an s-7 needle jet, but it’s very stuck. From what I understand is I am just supposed to push it down from the top of the carb and it will fall out. By I have been very careful not to damage the brass but no luck. I used the plastic handle of a screwdriver to pry down on it but it won’t budge. What do I have to do to get this thing out?
as for float height I am still not clear how to measure it. Is there a anyone who can explain it to me like you would to a toddler? I’m a hands on learner so it’s hard for me to understand via reading a forum sometimes
To remove the needle-jet, not trying to be insulting but just checking the simple stuff.. you do have the main jet and 8mm main jet holder removed first, right? Once those are out, the needle-jet usually only needs a slight little push from the top to fall out.
Not insulting at all. Yes they are both removed. I am pushing from the top down.
What elevation is this new setting tested for?
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The 125/150 setting has been ran from sea level to 5,000ft in a 125. May require small tweaks depending on exact elevation, fuel, or if it's a 150.
2022 and up Mystery Bog Update
Some will recall the topic of the 2022 and 2023 (MC125) Mystery Bog when running the jetting from this thread in a 125. Basically, quite a few folks have experienced a significant low to mid-throttle bog on the newer bikes. The bog can be significant enough that the bike is not ridable on an MX track. No one is totally sure why the newer bikes don't jet the same. Some think it might be different ECU ignition mapping related to the 2022 crank issue and ECU recall. In any case, I think I've got it licked.
In this post I talked about how I gave up on the Mikuni and went with a Keihin on a 23 GasGas MC125.
https://www.vitalmx.com/forums/Tech-Help-Race-Shop,42/KTM-HUS-125-150-2…
I ended up much leaner on the needle than would be expected for a 125 so I went back to the Mikuni and applied that same logic. Sure enough, a leaner needle got me in the right direction and now I've got the bike ripping on the Mikuni. I spent 3 days of trying many combos but, essentially, I ended up on the needle recommended for the 250/300 on page 1, had to raise the needle higher, bigger pilot and bigger main.
Here are the exact settings now:
2023 GasGas MC125
AvGas 100LL, Motorex at 40:1, vented airbox cover, FMF pipe and 2.1 silencer
Pilot 37.5
Main 540
Slide JD #5, no extra notch
Needle 42-75, clip 3
Needle Jet S4
AS 1.75 out
So far have run this jetting at 80 deg/4500ft and 70-90 deg/1400ft. Great at both. Going to experiment a little more with the 1/2 clip richer 43-75 and a few other things just to see if it can be made more perfect but it's really good right now. Note that if you are running fuel (pump or non-oxy) other than AvGas you likely will need leaner pilot and main than what I have.
Here's how she sounds.
Hey I got a jetting question for ya'll if you don't mind.
Just bought a 2019 KTM 250Sx that's been turned into an enduro/trail bike already. Big gas tank, 18" rear wheel, etc.
I know the 2019's SX's had different setting from the factory, and I'm getting confused about which way to go jetting wise.
If someone chimes in and says, "just buy the JD kit and do the block gasket replacement" , that's fine, but if you have some specific number for me jetting wise, that'll be cool too.
Details....
Riding style/type: woods, tight trails, a few fire roads. Def not motocross.
Bike: No motor mods other than a fly wheel weight. (no head mods or anything, stock muffler)
Gas: I'll be trying to stick with ethanol free 91 octane pump gas
Elevation: 7k feet
Temp: usually around 60-75 deg F, really dry air normally, not humid
Thanks!!!!!
Keep this updated and when you’re confident with it I’ll add it to the first page.
The jetting on the first page will work for you or get it very close. I know there are a bunch of guys at 5k running the jetting, but I’m not sure about the 7k.
Hey guys,
i have a 2019 KTM SX 250 where I rebuilt the engine and now rebuilding the Carb. I just ordered a 5.0 Slide and a S4 Needle Jet. I had installed a JD Jetting Kit a while ago and now I´m not sure about the needle I will need. Can I Still run one of my JD Jetting needle or do I also need a new needle.
The Bike got a Vforce4r and a DEP Exhaust system.
I Hope you can help me.
You need a different needle. I’m not sure what one you’re gonna need tho with a 5.0 slide. Thats still on the rich side for the 250’s.
Thanks for the help!
I thing I will start of with my old carb settings and my old slide since my whole engine is brand new. After break in I will try the new settings with the new slide. I order the 5.0 Slide because I thought the 6.0 Slide would be to lean. I will try the lean JD Jetting Needle first and then see how it goes with the new Slide and new needle jet.
Have you taken a look at the PC jetting web page and/or the jetting sub-forum on KTMtalk?
Keihin conversion simplifies life. As I'm sure you've read.
Circling back with a continued rich condition on my 2017 KTM 250sx per the spooge leaking from my silencer (and smoke from the exhaust across mid/upper RPM)
Bike has very good compression (~190psi). I ride at around 800' elevation pretty much always.
In 2021 I replaced the jet block gasket (didn't affect rich conditions) and (per this thread) and changed to the following jetting, which also hasn't really helped the rich condition:
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
Block seal was replaced in 2021 and still looks OK today:
Any advice or further things to try?
After posting I pulled the float valve seat out, and the O-ring fell apart the moment I put my pick tool on it. Would that O-ring leaking cause overly rich conditions in spite of jetting otherwise being to spec?
Ha! PC specs are joke. Both in general and especially for any Austrian bike with a Mikuni. Those specs only address pilot and main and assume you will use the stock slide and needle. They also assume you will use either MRXO2 or C12.
Didn't know that. So off to TT or KTMTalk.
Yes it can by letting more fuel into the bowl since it’s going around the valve. Depending on how bad that o-ring is it normally leaks onto the ground as well.
Pit Row
Would dropping from 500 to 470 be safe? I am pretty slow, and torque my bike around the track more than I am running hard in upper rpm. I ride at roughly 800' elevation.
Shouldn’t be a problem.
If you don’t open the throttle fully, the main jet has actually little impact on the mixture. The combination of needle and needle jet plus the offset of the pilot system is the important parts for most slow to intermediate guys that don’t ride very deep stuff or aren’t very heavy.
I always went one size down from the recommended setting (KTM for Keihin carb) when I was riding hard pack and stuck to the recommended settings when the track was deep or when I felt in shape and could push.
While carb is apart I discovered the float height was 7.3mm. I'm reading that would cause a rich condition. I set it to 8.5mm, and will reinstall the 500 main so as not to change too many things at once.
Question on throttle cable routing. I wasn't able to rotate the carb far enough to access drain plug, the cable wasn't long enough. Should I route the throttle cable behind the handlebar for that extra clearance? I am not running bar risers.
Standard routing is behind the bars. Yes, it will be very tight and not give you slack to rotate the carb if it in front of the bars.
Yes, put everything to spec (float height, this dammed o-ring, check the spark plug, air filter…) before playing around with settings.
where are you guys at jetting wise on a 2022 Husky tc with a 150 cylinder ? I just bought a low hour bike. only rode for about minutes on it so far but I do feel a slight boog when hitting the throttle. It will be my moto cross bike for a old slow guy. Thanks
If you read back through a few pages they’ve had issues with that bog and it didn’t matter what jetting or carb swapped into the bike it never went away. There is some solid jetting those guys worked to, but for some reason the 2022 125/150 has the bog.
I got one of the newer bikes running great. Check my post on page 32 with the video. Basically it needed a leaner needle than the older bikes to get rid of the rich throttle-snap bog. I had the same finding using a Keihin on the same bike - needed a leaner needle than the older bikes.
Thanks guys, I will give that a try. Looks like I better order some jets and a slide. Does the Lectron get rid of the bog at all? Thanks again.
Lectron is a totally different ball game. Yes, it can get rid of that bog, but it may require a little fiddling to get it perfect. They are not always as "Plug N play" as they are made out to be. And a Lectron will cost a whole lot more than the parts for the Mikuni. You may not hit the target first try on the Mikuni. It likely will require some fiddling and fine tuning to allow for the your local conditions and fuel and oil mix.
Giving this a shot! First post, but read this whole thing and just trying to get some clarity. Need the bike up and running Friday, so exhausting all options:
2020 125sx - few questions abut jetting for my race bike as I am short on time needing it this friday.
-VP T2
-Bud Racing MX High Compression Head (set to 0.0 deck height
-KTM Spark Plugs
-Wiseco Racer Elite single ring piston
-FMF Fatty
-FMF Shorty
-VForce Reeds 4
Racing at 0-2000 feet
Temps will be 40-65 degrees
I have been told that with these heads/inserts and T2 fuel, these bikes love fuel.. So, what would you recommend for jetting?
Currently run (Pre BUD head, Vforce Reeds, and new top end/piston):
MJ-520
PJ-32.5
Needle - 43-71
Clip - 2
A/S - 1.5 out
Cut the slide? Go with Yamaha needle? Slide jet #4? JD KIT useful (aside for gasket and oring)? What size jets and clip position (all due to oxygenated fuel, lower air temps, and hi compression).
THANKS SO MUCH!
Any help fellas?
Post a reply to: 125/150/250/300 KTM/HUS/GG jetting thread