WR/YZ426 Jetting in Colorado

I am wondering if anyone in Colorado has some good jetting for riding around here. I generally ride anywhere from 5,000ft to 8-9,000ft. I have a 2002 WR426 I have converted the timing to YZ spec and also have a White Brothers E-series exhaust on it. It just seems like the thing doesn't have nearly the bottom it used to and my buddies WR400 will out drag it everytime. Any suggestions would be greatly appreciated, most of the carb settings right now are stock and the muffler has 12 disks in it right now.

Thanks for your help.


I'm in Fort Collins and I have an 01 that I updated the jetting to LarryCo's settings. Do a search for LarryCo under the WR400/WR426/WR450 forum. You'll find a lot of info.

Thanks a lot for the info, I think I found all i need. I do have another question though, were did you get all these jets. I live in ft collins as well and when I have been to the yamaha shop they have only scratched their head when I told them what I wanted.

You can get them here at the TT shop, or Sudco www.sudco.com/ :)

Oh by the way, the JD jetting kit would simplify your life. There is alot of experimenting with needles and jets, air and fuel jets. You may have to change the needle clip position only on JD's needle, saves alot of time that you could be riding instead of working on the bike.IMHO :)

Not many of the dealers will know what we did to these bikes. You need to make sure you do the BK mod. Mine was squirting for 3 1/2 seconds and I was fouling plugs like crazy.

I got the parts at Sudco as well. LarryCo did a ton of work with Taffy to get this jetting right. I just copied his and left it alone. It runs great this way and there are many people on TT who also run this setup here in Colorado. JD's kit may work fine for you and it may not, I can't give you input on this, maybe someone on the site who lives in Colorado can.

I can't comment on the Yamaha shop here in Fort Fun anymore. My son is very good friends with the son of the GM and I don't feel it would be right for me to say anything either way. I've given him some comments and hopefully, he'll fix some of the issues. You've been there, you know. :)

Where are you in Fort Collins? I live off Timberline, South of the Movie theatre.

If you need to get jets and needles, I would go with the JD kit available through the TT store. It would be just a cheap as buying jets and needles from sudco and it is a great setup. My jetting is in my signiture if you're interested. :)


I also bought the JD kit and live in Highlands Ranch. The JD kit says to use the red needle and the 165 jet for high altitude riding. I didnt see anything about other instructions, but it seems you have possibly improved his findings for our riding areas (basically= high country). Do you recommend making other jetting changes in addition to what JD recommends in his kit as I see you have done? I would be interested in giving it a shot if you can tell me how to optimize the use of his kit. Or maybe I dont need his kit????

Thanks- Disco

I think in the kit, JD doesn't mention changing the pilot jet. I haven't tried putting my stock pilot jet in and don't think I will. With the 38 PJ I find that 0 to 1/4 throttle is perfect and if I ever have to fine tune, I just tweak my ZipTy pilot screw a little. Every bike seems to behave a little different to jetting suggestions. The best way to find out what the best jetting is on your bike is to record your jetting changes and how your bike runs throughout the throttle ranges. Then try one of our settings to see if it works for you. The adjustible Pilot Air Screw (only available through SUDCO) under the intake bell of your carb is also handy to change, but you may not have to so I would leave that towards the end of your jetting changes. Also, your jetting will change depending on the temp. During the summer, I had the red needle at the #2 position. When the temp dropped, I had to richen it up a little so I raised it to #3.

Vmax CBR dude thanks for the help, it sounds like I could go either way and still end up pretty good. I live outside of windsor south actually I usually just say fort collins cause people know where that is, and I go to school up here. Anyway thanks a lot for the help.

Danno :)

I'd say wicked_crash answered the question I had. He has LarryCo's jetting and the JD equivalent. Either way, I'm sure the bike will run a lot better. YZ time the thing while you are at it and you will be much happier.

Yo Vmax-Cbr Dude,

Havin a good winter? Hey, with the jetting we run, my plug is still quite white. I know people here say it doesn't matter, but it does to me, I want to tan it up a little. Since you're a little leaner than me, what color is your plug running?

Also, I'd like someone with me thats done it before when I YZ time. Are you interested?

Lemme know.

Unless your "jetting gifted", I would go with the JD kit, I tried Larry's jetting and had trouble dialing it in, remember I’m jetting challenged, so I bought the JD kit and dropped the needle 2x and she runs like a champ, very easy to dial in. My 2 cents.

Hey Steve,

My spark plug is usually a light tan colored. I still have some issues in the winter with the thing fouling plugs and it's probably the Winter Gas. I was running the PMB insert and I'm now running the FMF Q so I need to richen it up a little.

I could probably help you with the timing. It's very easy to do. We'd just need to set up a time. I'm so damned busy right now with the 3 boys and work it's unreal so it's hard to do anything spur of the moment for me.

My dad bought a new CRF250X so hopefully I'll get to rail that thing soon and see if it's a bike I'm interested in getting next.


Thanks for the reply. It is very easy for me to do something like this spur of the moment, so I could accomodate your schedule really easy. Mainly, I don't have the small torque wrench required, i assume you do. So, I could have it all torn down if you can give me a couple hours notice some time, then we can just do the inside the head work. Sounds like you are quite happy with the change.

If you don't have time, don't even give it a second thought.

Still got my number? If not, I'll pm you.


I had actually written the same letter to James Dean of the JD Jetting kit in mid-December, and this was his response:



There are instructions included in the kit for high altitude riding. The

exhaust has less impact than the altitude. Use the Red marked needle as

described in the #4 position, or #5 in winter. The main jet #168-170 in

winter, and higher up run the #165 to 9000ft and #160 when it feels like it

needs it, above 9000ft.

See the instructions for more details.




As this is my first summer with the JD kit, I'm going to give his advice a shot. Hope this helps. :)


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