yz timing

I just puchased a hold over 01 WR 426, can anyone tell me how to convert it to YZ timeing and is there a Quiet exhaust? The bike is street legal but very loud without the baffle. anything els I should do to make it the ultimate street fighter?

Hey millertyme

Start off with the throttle stop mod:

Take the carb off the bike and while looking in the throat open the slide (watch out because gas squirts out) notice how the slide goes up half way, restricted by the throttle stop? Now remove the throttle stop and start trimming (little bit at a time). Re-install the throttle stop and move the slide. Keep doing this until the slide just barely clears the throat. Put a drop of permanent Loctite on the threads of the throttle stop, tighten up, and that’s it.

Also before you take the carb off, try the search feature at the top of the page for:

BK mod

De octopus

If your like me and don’t like to take the carb off more times than you have to, you may want to do say the throttle stop and the BK mod at the same time.


thanks for the tips, by the way what the hell is the gray wire mod? I asked my mech. at the dealer where I work and he was clueless. Also when I asked him to change my timing to YZ he said why didn't you just buy a YZ. Guess I am on my own with this. Can't wait to blow the side panels off his YZ250f!


The '01 doesn't have the octopus. It uses an air cut valve but don't plug it unless you have problems. It is much cleaner than the octopus was.

The throttle stop is the first mod. Always do that.

The airbox lid and snorkle go in the garage where they belong (unless you ride in rain much).

The grey wire gets clipped or pulled. This changes the ignition timing back to YZ specs.

Something happens to the exhaust (pull baffle, new silencer, new pipe and silencer, Vortip) unless you need the ultra quiet power robbing baffle it comes with.

The YZ cam timing is common. Motoman393 has the original dirt rag article and pictures of how to do it. Only suggestion is as soon as you get the cams aligned (E in front and I in back square with top of head), zip tie the chain to the intake sprocket. Count the 12 teeth positions to the exhaust sprocket and mark with a Sharpie. Only then take off the exhaust cams and skip a tooth. Changed mine (severalth time) last night in 15 minutes. First time was closer to an hour.

BK mod is carb Accel Pump tuning and can wait a little while.

These should get you started. Use the search button for each.

Good luck,


I would like to add a couple of things to Motoman393 & Marks excellent description on changing your cam timing to the YZ spec...

1) Make sure the frame under the tank is clean. Dirt and sand will have a tendency to rain down into the head of your engine..

2) Do not allow the engine to rotate once the camshaft cap has been removed - it should remain at TDC until the job is finished. People have screwed up their timing because of this.

3) When you remove the cam cap, there is a half round clip inside that will seek to enter your engine cavities. Be prepared to catch it. If you miss and it drops in don't panic - go to Home Depot and get a magnet on a telescoping wand and simply fish it out.

4) The Yamaha manual has more tips on camshaft removal and installation, it would be a good idea to familiarize yourself with the appropriate section.

5) If it is in good condition - you can reuse the camshaft cover gasket.

[ May 09, 2002: Message edited by: z4me ]

Sweet tips guys I thought I made a bad move when I first rode the bike. Did the throtle stop mod and pulled the gray wire tonight. Can't wait to ride it tomorrow. Going for the bk carb mod and timing this weekend. Mark said removing the gray wire puts it back to YZ specs whats with that?

Millertyme, I really like your handle.

I should change mine to millerlitetime.

I noticed very little difference when I clipped the grey wire. It did seem to help from low to mid rpm range. I believe that this lets the ignition advance a couple of thousand rpms sooner.

The major return for the free mods is to lose the airbox lid and cut the throttle stop to 23mm. I should of done the BK mod before these because I barely noticed the difference.

I've gone back and forth with myself over the YZ cam timing. I think the main reason I haven't is because most of the posts I read all said more power and some felt it wasn't as controllable as WR cam timing. I ride mostly in tight woods, 1st thru 3rd gears usually, and the extra power might be more of a disadvantage. I like, make that love, the ability of this bike to ride some hellacious, is that a word, wheelies. I've never felt as comfortable on a 4th gear high speed wheely as I do with this bike. The power is very smooth and easy to control.


On the 250F forum I have a 'CDI 101' post that describes how the CDI works and after that, what the grey wire does is easy to understand. After the airbox lid and removing the baffle, the grey wire was what woke up my bike.

Good luck,


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