Jetting for a 2002 WR426

I have a 2002 WR426, I have adder a FMF Q pipe and cut the throttle stop removed the airbox lid,and cut the gray wire. I have been trying to get the jetting correct. I went to 45 on the PJ and have tried several different main's. The bike runs good at low end but runs crappy at high RPM,s. Has anyone out there jetted a WR and if so what are you running.

Use a YZ needle, like the OBELN or OBEKN, 3rd clip from the top. Try and do the BK / GB mod on the accelerator pump ( Search for Instructions)and reduce the squirt duration to less than 1 second. Keep your present stock pilot and pilot air (42 -75) and keep the main at stock 165, due to the Q muffler being some what restrictive.

Thanks for the input. I went up on the PJ to get rid of some lean popping, and tried several different Mains. I am going back to stock settings to see what happens. The problem seemed to start when I took the lid off the air box, I had the snorkle off and it ran fine. I will try the new needle and setting next.

My bike has a 45 pilot, 75 paj and a 165 main as stock. I did get a 38 pilot and 160 and 170 mains when i bought the bike in a plastic bag. I was thinking of going to a 48 pilot and a 168 main to idle better and possibly get rid of some breakup on the high end. My pj is 2.5 turns out.


The 48 with the 75 pilot air will almost certainly foul your plug. If you intend on using it, you should use a 100 pilot air.

That would be "Your Fuel Screw" is 2 1/2 out


You will be happy with the ELN needle. I have been all over the jetting range and happiest with the following

42 pj

75 paj

eln #3

165 mj

200 maj

Running stock pipe with modified vortip. You should also consider YZ timing, makes the bike a lot more fun to ride.


I checked my bike again tonight. I thought I had a 45 pilot but it is a 42. I may try the 45 with 168 main and a ELN needle. For some reason once the baffle is removed my high end breaks up pretty good. Doesn't seem to do that with the nasty stock baffle in. (Waiting on Yamaha's new baffle.)


RonO, you probably got your jetting figured out by now but if you go to the 45/ELN/168 from your 42/165 (not sure if you're running stock needle but I assume you are), that would put you more rich on the low end, leaner about 1/8-3/8 throttle, and 3/8-WOT you'd get your richer mix. That might help your high end and low end if you're looking to go richer low also. If you 1/4 throttle is spot on, you may need to look at keeping your needle the same and just bumping the MJ up for the high end. Depends on what throttle position you're having the problems at. If it's just higher than 1/2, the MJ will adjust it. If your mid is off, adjust the clip position. The best way to see changes is to get James Dean Jetting Guide (here on the TT store). It shows you graphically what will happen relative to your current jetting.

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