Upgrade to enjoy this feature!
Vital MX fantasy is free to play, but Premium users receive great benefits. Premium benefits include:
- View and download rider stats
- Pick trends
- Create a private league
- And more!
Only $10 for all 2026 SX, MX, and SMX series.
AJ specs work. The key is the slide,
I haven't got much time to update his jetting thread but saw this and want to confirm his specs work.
I also tried the 17-62 needle with same leaner slide and jets and it's also a very usable setup.
I'm running 96 non ethanol fuel, slightly oxygenated at 50:1 with Maxima K2
Did all this with a 470 MJ since it's all i had on hand at that time but going to bump to 480 or 490 this WE
Stock slide is too rich and you'll chase you tail if you keep it regardless of needle and jets.
I ran a 5.75 and it was too lean for me.
I also put some time with a 5 and it was already a drastic improvement.
You can’t go wrong with the 5.5 you ordered. I also tried a 5.75 and it was too lean.
The Shop
Free shipping: VITALMX
Luxon 4-Post Bar Mounts
$189.95 - $239.95
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
Just came back from riding , only swapped for a 480 MJ before.
Temp was low 80 but still 80% humidity (gotta love Florida for that...)
The bike ran amazing. Crisp, no bog, nothing wrong whatsoever and never had to mess with jetting from early morning low temp to higher later in the day.
Thanks again AJ!!
MJ 500
PJ 35
AS 1.5 turns out
Needle jet S4
Needle 42-75 on the 3rd clip
Slide stock that I cut and notched to 5.5ish.
PV 1.75 turns in from all the way out
Ethanol free 90 octane mixed 50:1.
Vhm high compression head, vforce4, pps exhaust system.
Squish set @ 1.5mm like spec sheet from vhm recommends, iridium sparkplug. Mobil 1 racing oil mixed @ 1/40, gearing 14-49. Pirelli paddle tyre, sandtrack but not to heavy.
Temps when riding were around 20c°, 6BFY 44-73 in the middle clip, AS 1.5 turns out, 450 main, 42.5pilot. Stock needle jet and slide.
Of the bottom it did not pack much, had to clutch to come out of the corner. After that it was a rocket.
Also first serious ride after rebuild, have a separate topic regarding that.
I think jetting is off as for the rest everything is working perfect, plug was dry, ring was clean, isolator was dry black with white spot on the back. Exhaust tip was dry.
I think about putting larger mainjet and try 40 pilot.
Also have jd kit from my te 300 to try.
Or maybe i may not compare to my te300 2017 i also used for motocross before the tc, this with 13/52 gearing and same paddle tyre. This bike did not hesitate when exiting the corner.
I have number 5 slide, and the s4 needle jet with the needle, need to try this on the tc.
Tried the 5 slide with needle jet and needle, 37.5 pilot , 440main on my te300 this and it was to lean to ride. Even on the street...
The pilot is way to rich and the main is way to lean. Most of us are running 480+ on the main and in the mid to low 30’s on the pilot depending on the temps you’re in.
Swap to a 42-75 needle and put the slide, needle jet, bigger main and smaller pilot richen up the fuel mix to 50:1 and see how she runs.
Don’t waste your time with the JD kit. It’s a bandaid fix at best and doesn’t run near as well changing the slide.
Also 14-49 in the sand is not ideal, 14-50 of 14-51 makes it better for sure.
Higher compression aids in the lower rpm, more grunt but top end will suffer a little bit. I know... Bike does not sign off early with this setup... For the woods i have my te300.
Jetting used came out the manual, as i did not want to mess with brass first time riding again, also to get a baseline of performance.
Next time out I will try other setting, also winter now. Temps are dropping, rained alot. Want to keep jetting safe in, for sure with the sandtracks we have here...
JD red needle in my 300 worked good, comparable with the s4 needle jet with 42-75 needle. With 5 slide way to lean?
Gearing is on the heavy side, but for sure this motor has the power to spin the wheel without clutching.
Just need to unlock it with good setting i think. Back in feb i used 14/52 and did not like it at all.
Pit Row
MJ 480
PJ 32.5
AS 1.5 turns out
Needle jet S4 from the off road models (stock is S1)
Needle 42-75 on the 3rd clip
Slide 5.5 (Kawasaki part 16025-0002)
PV 1.75 turns in from all the way out
Fuel mix 55:1 with 93 pump
So it sounds good on the stand. Good response. Took it out to a decently sandy/soft track. Top end was great. Felt good and crisp, although could probably go up one on main and make it a litter better. What wasn’t good though was around 1/4 to 1/2 throttle under load. Pretty positive it was detonating (kind of sounding like there was a nut shaking around inside my cylinder... kind of like chatter). So I did easy change first and changed pilot from 32.5 to 37.5 (didn’t have a 35 on me). It didn’t change anything. Then lowered the clip to the 4th position (second from bottom) and I feel it made it a little better, but definitely still detonation present. I’m sure dropping it to the 5th May have helped more, but I was done for the day... and probably wouldn’t have eliminated it.
With that said, is the needle too lean for these cooler temps? Slide too lean? I’m absolutely no pro at jetting/carb specs and am new to making changes.
I have this setup on my 19 .
only small diff is 50:1 (96 non ethanol, slightly oxygenated) and PV is 1.5 out
Disclaimer : C minus rider!
I rode last week end when temps were finally cooling off and the bike ran great, best ever since I had it.
Going tomorrow to Bostwick Mx Creek, temps cooling a bit more.
I'll report back
Need to be warmed up good, like any smoker then it just rips . I have zero complains, other than I can’t always keep up with it !
Temp went from 65 to 75 and never feel the need to touch anything .
Stock pipe and 304 PC silencer
I hated my 17 until I put a Keihin. Sold it to a friend and I still sometimes put some laps with it.
He’s way faster than me and love the setup I have on the 17.
Yet he thinks the 19 with AJ Mikuni setup is have much better .
Same for me.
I'll pt onefor next ride.
AJ, do you think i could benefit from a 35 PJ?
Jets swap is no big deal but it's running good now, so i'm getting less picky.
ADK MX, Fort Ann, NY roughly 200ft elevation
55 Deg F, May 8th 2020
Stock 2018 250sx minus pipe and V-force reeds. (I don't think it effected jetting at all in case anyone was wondering)
JD-Jetting Jet block gasket fix (Also not sure if this did anything)
37.5 Pilot
43-71 Needle, 2nd Clip from top (this clip position was the game changer)
Stock Needle Jet
450 Main
1.5-2 on air screw, just far enough out so it started idling clean
Post a reply to: 2018 ktm 250sx jetting and FWW