Need to find Ways to OPEN up my '02 WR426F - Please Help?!?

First let me explain... I live in the Boonies of Northern Ontario, Canada, I have an ancient computer and Dial-Up Internet and my computer makes more noise than a Detroit Diesel when I try to do a search for the Info... I know it is here somewhere but am fighting with this Dumb Computer trying to get it to give up the info :busted::bonk: . So if someone would be kind enough to link me to the info or possibly post the info for me, I would sure appreciate it...

I have a near MINT / Stock 02 WR426F. It has had nothing done to it... Stock everything including bars... Just put a Baja Designs QR kit on it, changed front sprocket to 15 tooth, new DOT approved MX tires and street legalled it. I would like - No Love to get more out of it and every site or person I talk to says you gotta uncork it!!! I know that there are tons of guys that have done it, but I was just wondering what is the best way!?? :excuseme:

Please Help????? :bonk:


Courtesy of Fellow TTer... :bonk:

Free Performance Mods you can do for a WR426:

cut throttle stop

remove airbox lid

uncork the exhaust

unplug the grey wire

YZ timing

ACV mod

BK mod

proper jetting (the best mod IMO)

It seems like I'm missing something :excuseme:

Do a search here on Thumper Talk for any of these mods to find out how to do them and if you can't find anything, ask away, one of us will guide you.

Here is a link that should provide some additional info.

To clarify and save you the pain of searching over dial up...Cut the throttle stop to the dsame length as a YZ throttle stop... 0.975 inch total length.

Uncork the removing the baffle in the end. You might want to pick up a GRT-R Quiet Insert to replace it. Quiets it back down a little.

Gray wire refers to disconnecting the gray wire in the 6 pin connector under the gas tank on the right hand side. Remaps the ignition to YZ spec. Be sure to seal up the hole in the connector so things don't corrode.

YZ Time refers to setting the exhaust cam timing to YZ soec instead of WR spec. Gives a much bigger mid-range hit and revs out better. You might also concider installing an 03 YZ autodecompression cam. Gets rid of the compression release and makes starting a whole lot easier. See the sticky on the YZ thread.

You might also concider adding a stock YZ pipe as a cheap way to boost power. Yo can find 'em on e-bay for about 30 bucks. Revs better, and is a whole lot lighter, too!

Thank-you Both for the ultra-quick response... It seems like my computer just finished sending the info and you guys had responded. I sure appreciate it. The only way to uncork the exhaust for me is to change it as in Canada they come stock with a Full Stainless exhaust with the tail-end welded in, unlike the American version with a removable exhaust tip. May have to look into a YZ pipe. Again Thanks....

Jamie :excuseme:

Just wondering if your spark arrestor mounts to the pipe with three bolts? If so, you may be able to buy a US spark arrestor to put on your bike. Then you could get a GYTR or Quiet Products insert for it.

Canadian version (02 WR426) does not have the throttle stop. Remove your airbox lid, change the exhaust if you like(ride stealth, get an FMF Q2). YZ time it. YZ timing is a personal preference(takes a little off the bottom, but builds revs fast in the mid range). Also one of the more effective changes(especially for bush riding) is to get the IMS tank with a YZ seat combo. The tank is bigger, and the seat allows you to move up closer on the bike. Have fun, the 426 motor was a ripper :excuseme:

Banffboy is right Canadian WR 426 has no grey wire if you go looking you will not find it . Canadian WR also comes with a YZ throttle stop so DO NOT cut the one you have . You can verify this by removing the Air box Boot and twisting the throttle all the way and make sure the throttle slide opens the full carb bore without blocking the bore. (US WR's only open the throttle half way) The canadian WR also comes with a richer carb Needle. (no need for JD kit) the best thing to do is get rid of the air box lid or at least the rubber snorkel. then get a new exhaust pipe slip on is adequite this will make a big difference (don't go too loud ) then jet the carb for your specific riding conditions . The BK Mod works great on this bike. Power Now works good and is a cheap mod especially when you have the carb apart. If you ride in a lot of wet slippery terrain then YZ timing may not be good for you (your choice)

I LOVE THIS SITE... I've just recently turned 34 and am just getting in to the the 2-wheeled mode of transportation... been riding race quads since I could start them... So I am needing a lot of help and I've been getting it from HERE mostly :bonk: If there are anymore Cannucks from around Ontario or even some of the NorthEastern States, you can also check out or search for Ontario Dual Sport Club. It has been another site with Super Friendly, Extremely Helpful, Bike Enthusiasts on it.... As I said before thank-you all for the excellent information and Keep the rubber on the road.

Sorry had to fix the link :excuseme:


I'm also way up in northern Ontario (Kapuskasing) with an '02 WR426F, geared 15/47 with Pirelli MT21's (130 rear/90 front) with BD dual kit. I've removed the airbox lid and backfire screen from the filter frame, added a PowerNowValve, FMF Powerbomb SX header, NGK CR8EIX iridium plug, and YZ timed it. I enlarged the muffler's outlet to 1 1/8" as well as shortened it 2". All the intake and exhaust mods require richer jetting, especially here at near sea level in colder weather. Mine runs flawlessly from spring to fall with a OBELN needle at position #2 with #170 MFJ, #85(drilled) pilot air jet, #38 pilot fuel jet and 1 1/4 turn out on the pilot fuel screw (underneath carb bowl). I also enlarged carb to head boot ID to match, and smoothed out intake inlet and exhaust port outlet...

I mix 40% 100 LL(low lead) aviation gas with 60% 91 pump gas to avoid pinging and for excellent torque, response and tractability, with some Lucas upper cylinder lubricant.

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