Need input from WR426 Owners Please!!!

I took my ’01 WR426 on its maiden voyage this weekend…what a thrill! :) I’ve upgraded from a ’96 XR250 so the increase in performance is huge.

Once you uncork the exhaust, open-up the airbox, and remove the throttle stop (I didn’t cut mine, I removed it…no problems yet) the bike comes to life! I did the seat and tank combo from IMS. While up on the tank, I can pull the front wheel up, in the first 3 gears, simply by twisting the throttle; with little-to-no effort, the wheel will come up in the top 2 gears with a little tug on the bars. I’m 5’9” and am tipping the scales at 210 pounds. So all of you skinny guys out there a REALLY rippin'.

A friend here at work rides a ’99 KTM380 and rides exclusively in the sand. He rides fairly aggressively and runs with CR/KX 500’s up any bowl. He has said that a WR/YZ 426 will pull him in the same race, so we’re DEFINITELY not lacking in power.

Go with the WR426...

I sounds like the throttle stop and baffle is the problem. I have heard you guys talking about removing the air box cover? Where is it located on the air box,(meaning left side, right side, or top)? Doesn't that open up your air filter for problems in the forms of dirt, mud, or water?


Oh, about the racing gas...on my friends WR and YZ426, if we don't run it we foul out our plugs and the bikes run like crap. The only time we can get away with running a 50/50 mix of Turbo Blue and 93 octane is when its cold.


The airbox cover is on the top of the airbox, under the seat. 4 bolts. Take it off. Just be cognizant of it when washing the bike. Clean your airfilter often. You shouldnt have a problem. As far as the fouling, sounds like a jetting problem. Im sure someone else will have a suggestion. (not my forte). :-)

Carl you wouldn't be by Cadillac would you? I have a place in Irons. Know where that is?


The WR is a 400 wheelies in 5th (YZ timing, all free mods, jetting by James Dean, $50 used YZ pipe). That WR your riding sounds like you're jetting is very lean. Fouling may be caused by either leaving the choke on too long (turn idle up a little rather than choke after 10 seconds) or you're giving it throttle within the first minute or 3 (depending on temp) and flooding the engine. These are temperamental beasts until the jetting is dialed in.

Try to religiously turn your fuel off just before finishing your ride so fuel won't slosh around when you're trailering.

First steps to carb after the mods mentioned above is *probably* a 45 Pilot Jet along careful pilot screw adjustments to smooth out the idle and off-idle throttle response, then experiment with larger main jets :)

BTW, I'm a believer in trimming the throttle stop or buying the YZ426 part. DON'T JUST REMOVE IT.

Good Luck! Let us know what you think after the free simple mods and a 45 pilot jet and maybe the next larger main.

If the bike still runs "slow", I'm sure there's a KTM550SX somewhere for you (dangerously unpredictable wicked fast bike, anyone have one?). Seriously, if it does run like crap, take it back ASAP.

You don't have to remove your air box cover, just remove the baffle and cut the existing hole bigger. Then you still have the perimeter of the cover to help keep stuff out. If you're worried about getting stuff in there, throw a nylon around the cover before you put it back on; that will catch a lot of dirt and dust.


I have heard you guys talking about removing the air box cover? Where is it located on the air box,(meaning left side, right side, or top)?

Ok.. the Wr 426 Is a Monster.. It will wheelie in any gear PERIOD and I weigh 270!.. Provided the Throttle Stop is modified. (and the exhaust baffle removed).

Out of the crate with the stop.. its a more like a XR400. However, Uncorked.. OH MY GOD! Ive NEVER had So much fun! Blows any of my Earlier YZs Away. Im a true believer in 4 strokes thanks to Yamaha. I used to think they were just too tame, with crappy suspensions compared with most 2 strokes.. Not anymore!.

Make sure you DO NOT use race gas PERIOD. 92 octane runs fine in the WR.. though My manual recommends 95 (im sure altitude is a factor and Im at 2200 Ft Above sea level). Ive heard from testing with 100 Octane and higher racing fuels.. the Wr HATES IT! And besides.. The o-rings in the Carb dont like full race gas anyway.

Throttle Stop should be Trimmed (or replaced with YZ throttle stop)..

and bring an extra pair of underware.. Ive almost crapped my pants first time out, and even now 3 weeks after buying and riding.All those Ive let ride it say "f**k this Bike RULES.. and all agree on calling The WR a real "sophisticated Monster".

If it does what it should.. you have 2 bikes in one.. ones for more "tepid" trail riding (stop in).. Without.. Shes a force to be contended with.

If Your Wr still doesnt pull wheelies..go back to your dealer and let them know.

Ive Had mine running close to 100 Mph.. and If it had a 6th gear.. I know it would run it. In 5th.. if you set your weight center.. she still wants to tug at the front wheel at higher speeds. Make sure you keep your weight forward if you do plan on taking a Rocket ride.. One thing I can say.. Its like nothing Ive ever ridden. Period. Yamaha.. You guys Really made one Hell of a bike.

Anyone whos ridden one will Vouch. This is one sweet machine.

Hey everyone. I just bought 01 wr426 and need help. its just not that scary fast that everyone is talking about. i have the throttle stop trimmed, the baffle removed from the pipe and the airbox lid off. i ride in southern california desert near sea level and usually warm and dry. any jetting tips? does anyone know if the 2001 wr timing is different than the 2001 yz? should i mess with the timing? I added trick gas additive to the 92 octane i bought at the gas station, do you think this helps or hurts? i want to make this thing screaming scary fast. please help.

If it's not scary're used to speeds that the average rider dreads. I've been riding a long time, and my '01 WR is scary fast...even after spending quite a bit of time on a CR500. So, if this bike isn't enough for you, I don't know what to tell you. Good luck...


Look at the carb needle postings about EKN and EKP (or EMN & EMP). These are from the YZ426 and will give the boost I think you're looking for.

James Dean

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