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Only $10 for all 2026 SX, MX, and SMX series.
2.1 hours on the bike
lowered 30mm front and rear
Gearing stock at the minute but have a 14 front and 52 rear to try out some options
power valve stock setting
10oz flywheel weight (beginner rider)
480 main
Stock pilot 37.5
42-74 needle 2nd clip
98 fuel @40:1 motorex
Still to try it out. Maybe get a run today. As everything frees off I know things will change.
Initial 2 hours of running in was interesting to say the least. The lean bog at 1/4 - 1/3 throttle was unreal on a stock 42-75 needle (from memory don't quote). Air screw super sensitive which had me playing with the slide straight away. Then found this thread. So looks like my thinking is along the correct path.
Will update as I go. Hoping someone can point me in the right direction or provide number 5 slide dimensions......
A little rich down low (loading up the plug slowly). Still have a hesitation about 1/4 - 1/3rd throttle but not major like before.
Temperature wise its up to 26C from about 22C last time out. So that might have contributed to the slight improvement.
Next, will take the slide 0.5mm further, go to a 35 pilot and position 3 on 42-74 needle.
Bike has 2.9 hours now.
The Shop
Luxon 4-Post Bar Mounts
$189.95 - $239.95
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
Will go to a 5 over the next few days and test again.
23 degrees C <1000ft ASL
35 pilot (1 3/4 turns out air screw)
42-74 Position 3
480 main.
Not adjusted the power valve yet.
Also thought I read in the manual for the 2018 that it has an S7 needle jet.
...more
42-74 needle 2nd clip
S4 needle jet
Slide 5.0
MJ: 490
PJ: 37.5
Air screw 2 turns out
MJ 500
PJ 35
AS 1.5 turns out
Needle jet S4 from the off road models
Needle 42-75 on the 3rd clip
Slide 5.5ish (I cut it and filed the front notch on the stock slide)
PV 1.75 turns in from all the way out
Ethanol free 90 octane pump gas mixed 50:1
When first started up warm it kinda wanted to load up a touch in the pits riding to the track. Cleared it out and it was fine when I got to the track gate. On track I had no hesitation and no loading up with instant throttle response everywhere and pulled hard all the way from off idle to wide open. For full disclosure I was at Cycle Ranch today and that is basically a sand track, which would require richer jetting because of being wide open everywhere. I did set a new PR lap time according to my LITPro though, so take that for what it’s worth. I’ll try the same jetting in two weeks hopefully at a different track to see if it loads up, but I don’t think it will of the temps are the same. I’m sure once it’s hot again the main and pilot will have to be dropped or maybe the pilot and the needle clip.
No power in low rpm, had to clutch every corner.
Had no opportunity to go to the track so took it to a nearby field to try.
TC250 2018
Around 7 c°
Sealevel
MJ 480
PJ 45
Slide #5, did not found 5.5 over here.
Needle 42-75 on third clip
Needle jet S4
AS 1.3 turns out
Float height 8mm
Jet block gasket not changed yet
98 fuel @ 40:1 with mobil 1 racing 2stroke
14/49 with paddle tyre, only ride sandtracks
Vforce 4
VHM head with their higher compression insert
PPS complete exhaust
I was happy with the result today, felt better!
Have to go to the track to confirm.
I will try smaller size pilot and bigger main, maybe try 50 tooth on the rear to aid with paddle tyre.
Thanks to digger & AJ for the great info!
For PJ, think will start safe and first try 40. Test it, and then determine if i go leaner. Prefer to have things a tad on the rich side
Forgot to mention i put in the yellow pv spring, 1.9turns in from fully out.
How is your roll on power? Lets say coming out 180deg turn, 2nd gear just above idle. You need the clutch?
I have no comparison for this bike, or baseline from new...
Sometimes detonation is your friend, it means you aren't far away from a good setting
https://www.youtube.com/watch?v=3w17-wLnLBI&t=3s
Looked like a fun race to ride, nice riding btw.
Hopefully we have some dry days left so i can go to the track for some testing...
These carbs take a little tinkering with to get right, but they are amazing and don't need much once dialed in. Totally changes the bike when its set right.
On the 300 the gasket was deformed, on the 250 starting to...
Both replaced with the jd jetting kits, tomorrow we go ride some enduro. Curious if i will notice some difference.
Happy holidays to you all!
Pit Row
Take it from 4mm deep to 5mm?
Thanks
To do the needle I leave it in about that position and use a long T handle to undo the two screws ontop of the carb, then carefully manuver the slide out.
All in main jet swaps are sub 5 minutes and needle adjustment is probably 10 minutes.
I have not needed to change the pilot much, but I think you can sneak it out through the float bowl plug with a small slot screwdriver using the same procedure as you'd use to access the main.
Your 17 has a different frame and tank so it might be a little different, but I think it's actually a bit more room. I swapped mains on a couple buddy's 17 300s and had no issues.
Here's what I run:
Vforce 4
HGS pipe and silencer
Jarvis mods (pinched overflow, holes to the splash cover and drain bolt)
Changed the inner sealing
adjusted the float heigth to 8,7 mm
slide #4 with filed groove
500 main
35 pilot
air screw 2 out
S7 needle jet
43-73 needle in 2. position
Runs good but not perfect. Little lag fom 1/4 zo 1/3 throttle. I will try different needle diameters and positions to sort that out when the weather gets better.
I made a little chart how Needle and Needle Jet interact. It's important to note that they form an anullar gap. So it's not linear how the combination changes the surface and therfore the flow rate.
Post a reply to: 125/150/250/300 KTM/HUS/GG jetting thread