To YZ time or not, pros and con, your input please,

Guys, I am thinking about doing this YZ timing mod, but, I am not sure it is for me. I ride trails, like low end torque, like hill climbing, and I really like hp. Love to roost. What are the pros and cons of YZ timing?

1. Does it give you more hp? or does it just move the powerband higher in rpms

2. Can the motor rev. higher with YZ timing?

3. Do you loose low end torque?

4. Do you have to rejet?

5. Should I try to do it myself or have a shop do it? :)

Any commments appreciated

1. yes, both

2. no, but it will have more power when you do

3. I couldn't tell much difference in low end. The mid and top end are noticably improved though, and that makes the low end look kinda bad.

4. no

5. I think that if you could change handlebars by yourself, then you should be able to do it. It's pretty simple.

Chris :)

If you want your engine to be more responsive, and have more mid range power, then YZ timing will give you this.

You may loose torque/responsiveness below 4000rpm, however the Power Now/James Now can more than compensate for this, hence this mod in concert with the change to YZ timing gets a more responsive and low-rev tractable engine. To respond to you queries:

1.) More mid range (ie the steepness of the HP curve increases above ~ 4000rpm).. little if any increase in absolute power at the top end

2.) No .. but more willing to rev

3.) Subjective response, yes below ~4000rpm.. interestingly the engine has a different audio beat when switching to YZ timing as the gas pulses change (my bike was also slightly louder as it flowed more gas)

4.) In my experience yes (and quite a lot 165MJ to 155MJ (YZ)at sea level). This may be atypical. I didn't expect it, but the bike was far too rich when the timing was changed.

5.) Do it yourself with care, using all available info.

In summary, adding a james now with this change should result in an engine with excellent attributes.

In my case, I did have to re-jet. Fouled 2 plugs in a row. They were both as black as could be.

So that might be different with every bike. I have heard others say the same.

It wont hurt to try the timing change first and then ride it and see how it runs before doing the jetting.


I have enjoyed every minute of the change to YZ timing. I really am a 90% trail rider so I feel qualified to give an opinion on this.

I rejetted, the bike revs faster not higher, It develops a nice little high rpm hit in the last part of the throttle, also easier to ride IMO because:

If properly jetted, the last half of the throttle is fun, fun, fun!! When you are on those tight trails, and you have to cross that creek and find enough grunt to go up the embankment on the other side, if you are in 1st you can roll on that throttle and this bike will climb like a starving monkey after the last banana! And it weill do it fast or slow, you decide. If you are on those long, steep, bouncy, rocky, hill it into 2nd and roll on the throttle, you will spew roost all the way up the hill, you will be much more stable at the higher speed, because you are going faster you are gonna sail over rocks and obstacles that would normally beat the snot out of you. Thereby allowing you to ride longer better faster without being as tired.

Because of the transmission in the WR you still don't end up wrestling the bike. 1st is still much lower and 5th is still much higher. If you end up taking a tight turn and being out of shape, you learn to blip the throttle as a correction rather than yank the bike around. The blip either pulls up the front wheel just enough to correct your line, or, in low traction situations, you can blip the throttle harder and slide the rearend around as a correction.

Cautions: in very very steep situations, and in restarting on a steep hill situation...GET FORWARD ON THE TANK!!... you have to be ready to back off and control the front end lift.

You will absolutely love this mod. There is a big difference between riding a YZ in the woods and riding a YZ timed WR in the woods.


There is a big difference between riding a YZ in the woods and riding a YZ timed WR in the woods.


amen to that!

Thanks for your input guys. I will do the mod myself. One question. When rotating the CAM, do you lift the chain off the cam and reset it to the new rotation or do you turn the CAM with the chain on? I assume you lift the chain off of the cam so as not to turn the intake cam, right? :excuseme:Also, the directions say to put a screw driver in the chain tensioner and turn it until it locks, I do not get that. Why not just loosen and pull the chain tensioner out?

You are on the right track. Take the chain off the exhaust cam sprocket and rotate the cam 1 tooth and reinstall the chain. You may have to remove the bearing cap cover on the exhaust cam bearings to get enough slack in the sprocket. Carefull with the retaining half ring for the bearing do not drop it in the engine! Safety wire the chain so you dont drop it in. Chain tensioner is spring loaded and one small turn snaps it back into the tight position. Just loosen all the way and make sure you hear it snap back after re-engaging the chain with the sprockets.


Would it help you if you could see a picture of the tensioner? I know it always helps me understand something better if I know what it looks like in there before I start to pull something apart. If so I can send you a pic or post it here tonight.

Im pretty sure the first time I took my tensioner out, I didnt even wind it up before removel. I just loosened each bolt a little bit at a time (keeping the tensioner even on both sides) until it came off. Then after looking at it, I could understand how it worked.

I've been watching this thread with a lot of interest as well. Changing to YZ timing does not require new valve shims, I assume?

I've only put about 1200 miles on my bike and I need to check the valves anyway. I was considering doing the YZ timing mod at the same time.

Do you need a new gasket for the valve covers when you remove them to do this mod?

From the information posted, it does not seem that this mod makes the bike uncontrollable in the woods due to the flywheel weight and wide ratio gear box. I'd love to have a little more snap and since it's free, it's even more attractive.

Thanks for the info.

Changing to YZ timing does not require new valve shims, I assume?

No. But you should check the valve clearances while your in there and see if they are within spec.

Do you need a new gasket for the valve covers when you remove them to do this mod?

No. Just be careful when taking it off. Its a pretty thick gasket. :)

Well, I YZ timed mine today. I have to say, I'm pretty impressed with the results. I did have to increase the idle a little but other than that, my jetting seems spot on thanks to Taffy/LarryCo.

Powerwise, I don't feel it's wild by any means. I also don't feel any loss down low at this point but I only rode it on the street for 1/2 hour.

Mid range to top end is another story. I pulled up in 3rd without the clutch, and shifted in to 4th just like I always do. The front started to come down just a little and unlike before, with just a little throttle, it goes right back up. Since I'm at altitude, it takes a little more to do things like this.

Anyway, thanks for all the info guys and I couldn't have done this without you guys and I used Motoman393's instructions. :):D :D

A few comments on the procedures if anyone is still considering this mod.

1. I didn't know where the bearing retainer clip was. Now I know there is one and it's right behind the cam sprocket and no I didn't drop it into the engine.

2. The carb needs to be moved a little out of the way to get to the cam chain tensioner.

3. It took me quite a bit more than 1 hour to do this but I could probably do it in less than 1 1/2 hours next time for sure.

4. I put a zip tie around the intake cam sprocket/chain to hold the chain from falling into the engine.

5. I wiped the exhaust cam sprocket clean in one area and put whiteout on the chain and one tooth so I knew where I started. That way, when I put the cam back in, I could see it was only rotated one tooth.

6. The rotor for aligning the piston at top dead center had a HI on mine. It took me a while to figure out that I needed to center that I in the middle of the viewing window.

I'm very mechanically inclined but I've never pulled a 4-stroke apart so this was pretty cool for me and I was pretty excited when I finished. It was very easy and if you haven't done it because you are nervous about the procedure, don't be.


The WR450 cam is plenty for most off road riding. I bought a YZ450 cam and installed it in February and after a month I switched back to the WR450 cam. It was too brutal for my riding. I noticed that the YZ guys are adding flywheel weights to compensate for the hard hitting stock cam. In this months Dirt Bike issue we see that Josh Demuth Arena cross champ had to add an 8 ounce flywheel and a WR450 cam to detune the YZ450 mid range punch and still managed to get more peak horsepower with a pipe and tuning. So I am glad to see others that think the WR cam is a good fit for our beast. I just find it easier to hook up and rip. Has anyone else gone back to the WR cam? :)

What did you do with the 03 YZ450 Cam?

Here at this altitude, we lose so much power that for me this should help a lot. Like others here in Colorado, I ride up to 13,000+ feet and at that point the bikes feel pretty enemic.

Anyway, I won't really know the full results of this mod until I get on the trail. I've always run 2-strokes so a little more hit shouldn't bother me much and the benefits should far outweigh the negatives. For really tight areas, I could gear down as I'm stock right now.

I did this mostly to be able to run with those pesky KTM 520's and 525's in the sand washes and high altitude fire roads. :)

I sold it to TT member NHKevin who is very happy with the extra power. I have not heard of any complaints from him. :D I have rode in Colorado before and you lose up to 10 hp because of the altitude. I know that a YZ cam may help at those elevations. :)

Hey guys,

I read something somewhere that said you cannot use the YZ or WR 450 exhaust cam with auto decompression in a WR426. Something about the pitch of the teeth on the sprocket being different. Has anyone else heard of this? is it true?

BTW, I did the YZ timing mod on my bike, and with the jetting in my signature, I feel it was a very good mod. I do not feel like I lost any low end. I am very happy with the mod.

I've heard something about that as well but I wasn't going to even worry about it until I YZ timed mine. You have to buy either the YZ or WR cam as they are now different. I wanted to make sure the YZ cam was what I wanted before I took the next step.

I know there is a ton of info on this site about the cam swap. That's my next move.



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