250-500cc 250 / 300 / 360+ Jetting Database

Year & Bike Model = 2011 WR 300
Carb = Mikuni
Pipe & Silencer = Stock/Stock
Other engine mods = None
Gearing = 14 tooth counter shaft
Premix ratio & fuel type = 40:1 Lucas 2-strock oil, 91 pump gas
Temperature range (deg F) = 55-85 deg.
Elevation (feet) =500-4000
Main jet = 390
Pilot jet = 32.5
Needle = It is a JD Jetting (red) but I don't know which bike it is from.
Clip position = 4
Air screw setting = 1 3/4 -2
Slide = 5.5 (Option for a 02 KX 125)
Conclusions/Results = Also have the needle jet from 02 Kx125. After many , many hours of testing. I have finally got my bike to run the way I want. The key to making it not so fussy was the slide. I have experienced the run good one day and like crap the next with the 4.0 slide, but I have ridden this setup a lot. From high speed in the desert, to slow single track in the mountains and it worked flawlessly. Very little smoke and NO spooge down the silencer. Also starts easy. I have to thank James at JD Jetting as he went above and beyond in helping me with this. Those of you that have a 5.0 slide, he has a blue needle that worked well with the stock needle jet. I think you could get simular results. I tried the PWK and I like the TMXX better now. And if you prefer the snappiness of the PWK, I found that grinding on the small hole (reed side) to make it wider, but not any higher, makes the Mikuni just as snappy.
And just so you know, I have ridden this set up in the very same conditions that when the bike was new, with the power up kit, the bike seized. I am not a fan of the GAY needle for high speed desert. (And I'm not high speed!! )

Year & Bike Model = 2006 WR250
Carb = Mikuni TMX38 (flatslide)
Pipe & Silencer =HGS pipe, stock silencer
Other engine mods = none
Premix ratio & fuel type = 50:1 and Putoline MX7 or MX9
Temperature range (deg F) = 64degrees F, 18 degrees C
Elevation (feet) = 900 ft 275m
Main jet =420
Pilot jet = 30
Needle = 6DJ8-60
Clip position = second from top
Air screw setting = 1 1/2
Slide = 3.0

Conclusions/Results = Rich in the bottom end (plug is black and wet), pulls hard from about 1/4 throttle to WOT (plug is brown)
I tried adjusting the Airscrew out (until 2 1/5), but it didn't feel much better, actually I believe it got worse (more blubbering), which is opposite what I would think in theory about turning the airscrew out (anti-clockwise), would make it leaner.

Would you recommend switching to a 27,5 PJ (I'm thinking that would be strange considering the Husqvarna template says around 35 and would be very lean), or is the slide wrong would a 4.0 help me.


Compression couldn't be the problem, piston is around 18hours old, air filter is clean.

I'm interested in a TMXX carburetor (found on >09 2t), so when anyone wants to get rid of theirs please have a chat with me. Also interested in a 4.0 slide for original TMX flatslide

With kind regards, Bart

Don't you mean 04 kx 125 the 02 has the old TMX?

I am sure you are right. I have not looked them up in a while and I have CRS (can't remember s..t)

Your slide is wrong. I messed with jetting in my 2007 for weeks, until my 3.5 slide came in, once installed the bottom cleaned up very nicely. I would like to try a 4.0, but they are currently unavailable where I'm at. I went from a 3.0 to the 3.5 and it was a huge difference. I'm running a 390 main, 32.5 pilot, and 2 turns out on the air screw. 40:1 Bel Ray. Bike runs very nice at 2000 feet, 75F. I'm running the leaner needle also, I believe it's the 61, 2nd from the top.

2009 WR300
PWk 38as carb
JD red needle 2nd clip
38 Pilot
152 main
temps in the 80's and 90's
elevation from 6000-10,000ft
Bike mods are Pro Circuit plat2 pipe, 296 silencer, and Husky Hi comp head

Year & Bike Model = 2011 WR300
Carb = Keihin PWK38
Pipe & Silencer = Pro Circuit Platinum 2 pipe + Pro Circuit 304 silencer
Other engine mods = None
Gearing = stock (13/48)
Premix ratio & fuel type = 40:1 Motul 800 + 98 RON BP Ultimate
Temperature range (deg F) = 12-20 C (end of winter temps)
Elevation (feet) = 70-500 metres.
Main jet = 175
Pilot jet = 45
Needle = JD red
Clip position = 3
Air screw setting =1 1/4
Slide = stock
Conclusions/Results = tuned the bike in summer with ~30 C temp and using 42 pilot jet air screw at 1 turn, 5 months away from the bike and back in cold weather had to go up to 45 pilot and 1 1/4 on the air screw.
Bike absolutely rips, brutal acceleration, 1-2 kicks cold + choke, 1st kick no throttle everytime when hot. Going up to 14 tooth countersprocket for the fire trails.