BK Mod??

Hey Everyone,

Thanks for all the advice so far. One more question...What is the BK mod? I have a 02' Canadian WR 426 and I have added the e-series pipe, taken off the airbox, got the thing jetted right fianally. The one weird thing is that when I hit the throttle quickly it seems to stumble at low RPM's...

I know the Canadian bikes dont have the throttle stop or the "grey wire" (I think) If I do this "BK" mod will the bike stop the hesitation?

Any suggestins?


put BK CARB into thr search engine in your upper right screen and look for a post by motoman393.

He's got excellent pic's and verbage for performing the mod. You should spend no more than

10 bucks on the mod. This is the next mod I'm going to put on my month old WR426.

Here in Texas we do have a grey wire and a throttle stop but they also can be handled for nothing.


Got your personal message...but I cant reply to you because you have this "disabled" in your profile. Change that setting so folks can respond to you...

Huskyrider is correct. Do a search. There's great pictures out there for the mod...and both a metric and standard parts list as well (actual Home Depot part numbers if I remember correctly!).

Yes, this will limit the stroke of the accelerator pump arm and thus limit the amount of "squirt" into the engine when opening the throttle. Most bikes (stock) have 3+ sec of squirt duration and I believe most folks are limiting this down to about 0.5 sec. By reducing this squirt, you will remove that low end bog and improve performance greatly. There's also a "timing screw" already located in the accelerator pump used to adjust the "timing" of the squirt in relation to the slide that moves down when you open the throttle. Read the post and/or take off your carb and manually turn the throttle cable attachment to see what I'm talking about.

I believe this mod applies to 2000 or greater WR's. Check on the right side of the carb (right side as your sitting on your bike) and look for a little "notch" on the outside housing (the pictures in the BK mod post should show this very clearly). If you have this notch, you should be able to do the mod (it's like Yamaha was going to put a screw thru there and decided not to for some reason).

Anyway, let me know if you have any other questions. Do your homework, spend $10, and you'll greatly improve your bikes performance...plus learn a little about your carb/acclerator pump!

Seems crazy that Yamaha would let their bikes come off the assembly line with that bog.. I get it any time I snap the throttle hard. If I have some RPMs its not as bad. I took it to the dealer and they told me I have to "roll on" the throttle...that is BS.

Does anyone in the Los Angeles area know a good mechanic / shop who can do the BK mod? I dont think my mechanical skills are up to par when an $800 carb in on the line..

The 02's aren't suposed to need it, but I'm sure there's exceptions. I read the post when Mr.BK himself wrote this statement. But if you don't like it you can alway's go back to stock. If you do it be sure to post your results so that we all can learn abit more.


I just did the Mod last night. Took about 15 careful minutes. I never even used a drill or a tap and die kit before and it was easy. Mark the exact spot you need to drill with crosshairs and draw a line representing the angle you want the screw to go in. Make sure you drill in straight and not at an angle (I almost screwed it up then noticed my hand was cocked sideways.) A 3/4" bolt is probably the best length.

Home depot sells drill bit and tap combo's for about $3 that are the right size.

One Question, what is the spring for? Seems to me it only keeps the screw from turning in one direction. Why not just use locktight?

Now for the interesting part, JETTING!!! :)


Hey SoCal,

How do you like the YZ timing? this is my first 4 stroke and I normally ride an 00' YZ 250. I like the snap of a 2 stoke, but I want power down low for this bike. The problem is I dont have the power down low due to this bog!! i think my bike is the exception to the rule, because I had the Yamaha shop jet it after many unsuccessful attempts on my part to get rid of that low end bog...it only happens off idle or deceleration when I hit the throttle hard.

Do you know why the 02's arent supposed to need it? Did they change the spay time length to be correct? Seems weird my bike still is a candidate...perhaps since it is a Canadian model it was assembled here in the US with an 01' carb.


thanks for your input, I will let you know how it turns out. :)


Ok Here goes.. I studied TT for months before I even got my 02 WR so I pretty much Knew where I wanted to go with it.(I think) I talked to a guy in depth who know's well a famous exhaust maker. He felt it is very tough to make a pipe that beats the factory pipes wide power band. The best aftermarket mfg can do is move the powerband around for certain applications and personal likes. Thus my choice was a stock YZ pipe. But the pipe does not seem to do much good without YZ timing, at least thats what I found on mine and others. When I went to YZ timing I have zero bog. Just a nice wide power band that when I want it to, it explods mid-range on up, very smooth and controlable too. Why don't the 02's need BK you ask? From what I understand it's mainly because of the re-maped ign. and possibly tweeked carb. Do I like my YZ timing? LOVE IT!.. I still have low-end and a$$ rippin roost to boot.



I just noticed your not too far from me. Just drag your blue beast on over and we'll tweek it a little or do your timing. Just don't pull a WRoost on me. I still feel guilty!.. :)



Your not set-up to accept p/m's

So I will reply here.

Omni ask's..Guilty of what?

Well it's a long bittersweet story so I shall try to keep it short...Once a long long time ago..A galaxy far far away... Oh, sorry wrong one. Anyway I met WRoost from here at TT. We talked off and on and decided to bring his bike over to re-jet and YZ time. Well it was a real Ciderrella (sp?) story we really hit it off, his wife came over met mine we all went to dinner, we all became fast friends..Well anyway Mar..er, WRoost declines MY offer to go riding and goes to a mx track in Riverside with his OTHER friends..Well I get a call from him telling me what a great job we did on the jetting and the YZ timing was awesome, everything was perfect!!..So perfect he's calling me from Riverside Hospital intensive care.. Turns out he WAAAAY overshoot's a double jump he's taken a 100 times before, ultra cases it, knocks himself out but still going strong, hits the next jump at mach3+ while still asleep. Does a flying W with a Superman mixed in for good measure and of course this is all before he's even hit the ground!!.. He wakes up in his new ride, with lites flashing and cpr and all that jazz going on. I firmly believe that his friends who are very well trained saved his life.. THANK YOU.. Results, broken pelvis, broken ribs, punctured lung, badly tweeked knee and ankle, concusion and a few other malidy's.. WRoost, if your reading this get well soon. I miss ya buddy.. Guilty? hell yes I feel guilty..


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