WR-250F with YZ Cam Timing - My Results Compared to Stock WR Cam Timing

I'm riding a 2002 WR-250F, which is my second WR-250F (foolishly sold my 2009 model).

With that 2009 model and with this 2002 model, I did all of the "free mods" and other uncorking mods that everyone else does, but always kept the exhaust cam timing in the original WR position.

That is:

Compared to a 2002 YZ-250F, my 2002 WR-250F comes with the exhaust camshaft advanced one tooth.

This means the exhaust valve opens and closes sooner compared to the YZ, resulting in less valve overlap, and, less power.

 

Or, so I had always read.

I always wondered if the smooth and very controllable power (which was also hard to stall in very slow going unless I simply made a mistake) of the WR would be traded away for more maximum power at higher revs with the YZ cam timing.

 

This week, I finally decided to retard the exhaust cam to YZ spec. and see what I got.

This morning before leaving for work, I took the bike for it's maiden voyage in this condition for a very brief 2-mile putt down the street to make sure all was well after putting it back together, as well to get a small sample of the results.

 

So far, the bike undoubtedly feels more peppy from just above the basement revs on up, as well as pulling through the revs with more force.

The low-end, as far as I can tell so far, is either unchanged or changed to a small enough degree that I can't tell.

Yet.

Basically, it feels as if it just received a shot of adrenaline which is quite noticeable.

 

In all of the posts I've read over the years, I can't recall anybody giving some kind of a detailed back-to-back comparison of WR cam timing vs. YZ cam timing, with the usual opinion being, "There's more power everywhere...", and not much else.

I've even asked others, who really like the YZ cam timing and always recommend it, what the comparison felt like, only to be told they'd never ridden the bike with the stock WR cam timing.

 

So, after this weekend's Sunday 43-mile trail ride (the real test for me), I'll write down in detail what the difference feels and performs like, and any pluses or minuses along the way.

Can't wait to hear the results. Been wondering if it'd be worth it on my 03.

Thanks for the input so far! Can't wait to hear a detailed description after a proper ride! My '01 WR has the cam rotated one tooth, to achieve the YZ timing and while I love it, I did not do a "back to back" test to be able to compare the two. My '05 WR is still running the stock timing, mostly because I'm too lazy to mod the decompression pin, and too cheap to throw out the needed coin for the YZ one!!!

 

Not2shabby, remember you can't just rotate the '03 on up models. You have to purchase the YZ cam or mod the decompression pin on your stocker before rotating it to YZ timing.

Went for my acid test ride of 43.8 miles, today.

The trails are typical Connecticut woods - the majority littered with rocks along with the occasional faster section where you can fly.

Here's what I found out and how I feel about it:

 

The power increase starts about where the low-end ends and the mid-range begins.

Power from that point and up is increased quite a bit, and the bike has a newfound willingness to rip through the revs when accelerating through the midrange and into the top end, making the stock setup feel as if you're sometime dragging an anchor behind when you want quick acceleration, as when coming out of some corners.

 

In other words, just as you'd expect from a motocross bike.

 

The bike revs much more eagerly now as if the flywheel mass has been reduced, and exiting a corner and opening the throttle has the bike leaping out of the turn, front wheel getting light and probably leaving the ground.

It feels very snappy and very eager to rev and accelerate from the bottom of the mid-range and up.

 

Pros:

 

The bike is, right now, basically a 2002 YZ-250F with a 3.17 gallon fuel tank, lights, and an off-road (FMF Q4) muffler as far as performance goes.

It flat rips.

In it's element, the additional performance is just what the doctor ordered and makes it easier to go fast.

In fact, the bike feels like it would rather be going fast versus going slow.

Places that allow some sort of decent speed, like faster trails (especially with whoops and jumps) that allow you to open the throttle are a good match for the performance.

 

On my favorite section of trail, today, that is whooped, has banked and bermed turns, elevation changes, and very much resembles a motocross track through the woods, it was my fastest pass through there, yet, as the bike had the ability to rip in these conditions with strong acceleration and quick rev.

Wheelies once the revs hit the mid-range are child's play.

All-in-all, it's a motocross powerband compared to stock.

 

Cons:

 

It's a classic trade-off with gaining such power in the midrange and top end, and what was traded to get it was some torque and lugging ability way down in the basement revs of the low end, just above idle and slightly above that.

This is the area you'd use while putting up a tight, tricky, rocky hill trail in what seems to be a gear high in order to keep traction with the rear tire, or winding through a thick forest trail that simply does not allow enough space to open the throttle and rip.

Way down there in the revs, while working the tightest trails, is where you notice this.

 

Compared to how much performance was gained, it does feel that more was gained than was lost, and the low end still is strong enough to trail ride.

However, you will have to become accustomed to the new characteristics of the powerband while working the low end through the tight stuff.

Where the stock characteristics made the bike seem tractorish and difficult to stall even at the lowest RPM, the YZ cam timing won't allow you to drag it down quite as far while under a high load without risking a stall.

By the mid-way point of today's ride, I was using very slight clutch slippage to help compensate for this, something that was effective and easy to do.

 

Verdict:

 

To be honest, I'm still on the fence as to whether of not I'll leave the bike with YZ cam timing, or go back to WR cam timing.

I'll probably go for another weekend of two in order to give it a fair shake and to really become accustomed to it.

 

The additional snap and performance is definitely welcomed and quite fun and easy to use to ride fast.

The catch is that you need enough room to use it, and for four years worth of trail riding, I'd been riding WR-250Fs with WR cam timing and found the added chugability very handy where it's useful.

 

So, it's a toss-up, very much as I assumed it would be.

I'll probably update this post in the not-too-distant future.

this is exactly the difference I found when i changed the timing on an 02 wr. The new setup just needed me to use the clutch a bit more. A rekluse clutch will help in the slow twisty's.

Personally, the OEM cam timing wasn't to my liking as it was just too slow revving and too hard to lift/lighten the front when needed, like over sand whoops and roots and small logs in the trail.

Now if somebody could just come up with a variable valve timing setup.  It's done in some cars I know of (Honda VTech).  Maybe the technology will come to bikes.  

My guess is that, so far, the added weight, expense, and complexity has not been deemed worth it.

Is this possible on newer than 03 models? I got a 12

Edited by ttrturd

Is this possible on newer than 03 models? I got a 12

 

Yes, but those who have done it report that you have to perform an extra step of grinding down the decompression pin sticking out of the exhaust cam.

This needs to be done with 2003-and-later models, the ones with no decomp lever on the handlebar.

Read here:

 

http://www.thumpertalk.com/topic/981587-wr-exhaust-cam-set-yz-specwhos-done-it/?hl=%2Bwr+%2Bto+%2Byz+%2Btiming+%2Bcam#entry10272946

Edited by YZEtc

I'm no longer on the fence about where to leave the cam timing at; I put the exhaust camshaft timing back to stock WR specification.

 

The harder-hitting power, increased horsepower, and quicker acceleration was just fine where it could be used properly and made sense, but reality is that where I ride the bike, conditions to effectively use the additional performance are few, and the loss at the low-end is noticed often.

Basically, it boils down to my needing the additional low-end torque more than I need the increase from mid-range on up.

 

Different riders and different terrain can result in different opinions on the subject, but at least I now know from my own experience exactly how the bike runs in both settings.

I have a 07 WR with a Wiesco 290 kit ( altitude compensation ) that is strictly a trail bike, stock exhaust even the air box boots . I have sets of yz cams laying around , but every time I ride the bike I can't come up with a reason to want to change the power delivery in any way. Way more benefit seems to be coming from suspension changes in order to get a good feel in the rocks at speed. So far the best change has been the gold valve kit for the compression piston.

Sound logic.

 

I owned a 2009 WR-250F, which is the same machine as your 2007 model, for a bit over two years before foolishly selling it for a 2009 CRF-450X.

The 450 had plenty of power and I enjoyed controlling that power, but using the upper part of the rev range was out of the question 90% of the time due to the tight terrain, and that tight terrain revealed that the bike felt a fair bit heavier while negotiating that terrain.

The heavier feel proved to be what made me decide to sell that bike after about 7-and-a-half months of trail riding.

So, I went back to another WR-250F, the 2002 model I ride today.

 

Do you have any experience you can tell me about how your bike runs comparing the stock engine setup vs. the big bore kit you now run?

Edited by YZEtc

Well when it was stock it ran ok but I have to ride about 10 mi of road to get to the hills and on the road between sections. And at this altitude it felt like a struggle for the bike. Now with the big bore I can run a tooth taller front sprocket ( 14 v 13) and only need to use low gear in the knarly sections and cruise at 55 easily . As for the power band it is the same but with more everywhere . It really makes the perfect trail bike. Yamaha should build a 300 for sure.

Have funimage.jpg

Sounds like I'll keep the WR timing and maybe do a big bore when it's time for new valves. Thanks for the info!

Sorry, I know that i'm getting this tread open again but i would like to be sure of what am i doing.

I have a wr250f 2005 and i bought the YZ250f camshaft.

I just want to be sure, when i'm installing the exhaust camshat of the YZ250f, do i need to rotate it 1 tooth clockwise or counterclockwise?

Does the dots on the cams need to be the same as original, or will the move?

Thank you very much for the reply.
 

You probably need to do it as shown in a 2005 YZ250F Service Manual, or search this site for installing cams on a 2005 YZ250F. 

It's when you are using the stock WR250F exhaust cam that you install it a tooth off from the original cam sprocket timing mark.

Forget what you read about CW or CCW- that applies to the 01 and 02 WR250F with a stock WR250F exhaust cam. For your 2005, you need to install the YZ250F cam with the cam timing marks correctly aligned per the manual.

Forget what you read about CW or CCW- that applies to the 01 and 02 WR250F with a stock WR250F exhaust cam. For your 2005, you need to install the YZ250F cam with the cam timing marks correctly aligned per the manual.

Thank you very much.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now