need jetting help

Could someone give me some examples for my jetting? I am going to try to do my own jetting and need a good starting point. I have a WR 426 with WB E-Series S bend, airbox lid off, Throttle stop trimed, and the grey wire cut. My riding is anywhere from 6000 to 10,000 feet. I hope that is enough information. Also does anyone know of a good book that would help me get started with jetting? I need something like "An idiots guide to jetting" :) . Thanks for the help.


The greatest resource is this site. Perform a search for "jetting", the results I used when I needed reference was excellent. The posts indicated elevation, Pipe, airbox or any other mods. You should be able to find an example of a setup that matches your own. One thing I would reccomend is a pilot screw adj. tool. It is a short 1 inch screwdriver with aknurled knob that allows you to adjust the pilot without any hassle

After reading a post on the YZ forum about plugs fouling if they rode there bikes for a little ways, shut it off and didn't start it again for a while. I think this might be my problem as well, as my bike only fouls pulgs when I go out to start it after it has sit for awhile. When I pull the plug out it is very black. The bike seems to run good but there isn't another WR around here to compare with. I should have my bike back together next week and I will ride it a little and see what the plug looks like. I am sure my jetting could be better so I will probably still try to work on it if I get the courage :) . I did a search on jetting but didn't find that much on the elevations I ride at.


01 WR 426, WB E-Series S-Bend W/12 disks, Airbox lid removed, Throttle stop cut, grey wire cut.

if you find "jetting Q's" in a search (it's only 30 days old) it has a link to a web site by patrick burns and you'll learn everything yo need there.

you could always try 160MAJ, 158MJ, EMN needle (code is N427-OCEMN), clip 3, 35PJ, 45/50 PAS (buy the screw, it's worth the extra money), PS 1.5 turns and your APJ down to less than .5 second of squirt.


After reading about 200 different questions and replies in the "Jetting Q's" thread,I now have a hangmans noose directly above my bike in the garage, I am now ready to put my head in the noose start the bike and ride off into oblivion. But I Can't !!!! because I can't get the fu#@!*# jetting right. Out of all those different scenarios not one of them has the same basic stock jetting or needle that I have. Looks like I've got a lot of homework before I can make that ride into oblivion, but no worries for all you '02 wr 426ers out there, I'll leave a note taped to my front numberplate with my final jetting entries scribbled on it. :)


I hear you loud and clear. If you don't want to do the whole Taffy setup with airjets, try the following:

#45 pilot

1 1/2 - 2 turns out


#165 main

The needle part number is: 5NL-14916-EN and is an option for the '01YZ250F. This jetting is very close to a YZ426 except for some small alterations. Expect the mid-range power to come alive more like a YZ426, great for wheelies.

Farmboy and BIGFOOT, with stock needle and jets try removing the checkvalve on the tank vent. The tank can build pressure when sitting hot and force excess fuel into the carb to flood it. Also try turning the fuel screw inwards to lean the idle and check the response. The plug may be black from simply having too rich of an idle mixture setting.

Farmboy, try a leaner clip position on the needle (#3 or #2) for your higher altitude riding.


I know what you mean about the Jetting Qs post BIGFOOT, it took me forever to read all of it :) . Thanks for making everything make sense James Dean, this is the first bike I have ever tried to improve and was feeling like I was way over my head. I appreciate your help also Taffy, I have written down your recommendations also, and will try to get more into depth with jetting as soon as I figure out what the heck I am doing :D . Thanks again for the help everyone.

in jetting Q's you don't need to know everything just know that they were valid tests and you can check out how any change felt to me whilst riding.

in many ways it's for people changing their jetting and needing some feed back more than people asking about the technical stuff.

for a technical appraisel the patrick burns write-up takes some beating.


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now