WR400 Questions.


I used to ride a YZ80 many many years ago, and I loved it. I have only recently established that I can get enough money together to get a WR400.

So with that in mind, my knowledge of engines and cars is reasonable but all the different technical terms with bikes has pretty much just left me stumped.

From what I understand the mods to go for are:

-remove baffle

-remove airbox cover

-change the cam timing

-remove the throttle stop.

My questions are:

1 - are these mods what I should do?

2 - what is a baffle?

3 - how much should the timing be changed, and should YZ400 cams be used?

4 - how is the throttle stop removed?

Cheers guys,

P.S If you know of any other articles that will get me a general understanding of terminology and other stuff, that would be great.

IMO, remove the baffle. It's in the throat of the airbox, under the seat. It may be gone already.

Do not remove the airbox cover except to access your air fliter.

Do not change the cam timing. WR timing is better for low rev lugging power, YZ timing is better for rev happy MX'ers.

Shorten the throttle stop to YZ spec.

Check the ThumperFAQ for more info.

Dale, I have a '99 400. This thing is plenty fast with WR timing.

I love the YZ timing on my 2000 WR. There is also a gray wire mod and an accelerator pump (BK) mod. I suggest you buy the YZ throttle stop (or shorten the WR one) and ride it as is for a while. If you want to tinker later you have plenty of time. Does you have a quiet exhaust tip insert on the Aussie models? That might be what they are referring to as the baffle. It is much louder without it but it runs much better. There are exhaust tips you can buy that strike a compromise in both sound and power between the stock tip and wide open. My airbox lid was already gone when I bought my bike so I can't comment on it. As the other guy said the baffle might also be in the airbox. Not sure which they are refering to.

The throttle stop is simply a allen head screw on the otuside of your carburetor that limits the amount that the throttle can turn. The YZ model screw is much shorter and allows full travel of the throttle. Some people simply remove the screw altogether but it is not recommended as it allows too much movement and may cause carburetor damage. Use the search feature and look for WR throttle stop photos. It is very easy once you find it. The other mods are more involved and are probably best performed when you have the bike apart for maintenance like valve adjustments or carb cleanings. To my knowledge the cams are the same as the YZ. You simply change the position of the cams relative to the timing marks for piston top dead center so in essence it is a free power upgrade. It is pretty easy to do but you must have a good understanding of engine theory or you could destroy the top end. There are very detailed directions on how to do it if you decide to. Enjoy. What months are your winter season there?

YZ timing or WR timing aside do the 450 cam mod. eliminates the "Starting drill" and saves a ton of energy. as stated above, best done when you already have teh valve covers off for an inspection / adjustment.

Throttle stop is a piece of cake and well worth it

my baffle and airbox lid were already removed when I got mine

haven't done the grey wire

mine has more than enough power for me to use.


Now: Replace/cut throttle stop. Cut gray wire. Remove air box lid. JD jetting kit. Power Now. Check and possibly replace throttle slide plate (cracking). Check valves.

Later: Open up exhaust - remove baffle or buy after-market pipe. YZ cam timing. Hot Cam with auto-decompression to ease starting.

Hey thanks for all the info guys.

I just looked at that ThumperFAQ site and it says how the YZF timing increases mid-range and top-end but drastically reduces low-range. I need low range to better preserve the engine, so I think that mod is not for me.

Other than that I think the thing in the airbox should be removed, a new exhaust is in order, because I need it for road use I can't just remove the baffle. And I also think I should get the YZF throttle stop.

For the throttle stop I would want the YZ400F one wouldn't I? As opposed to the 426 or 450?

One thing you might want to consider is to get a simple two-position handlebar switch and route the gray wire through it. Then you can have the WR igntion map (on) or the YZ map (off). Make sure you get the '99 YZ400F stop, just because the stop may have changed when the next generation FCR carb arrived with the 426 motor.

Hey another question here.

With the YZF throttle stop, approximately how much would it be and where would I source it from?

Also how much would it be for a full-exhaust that runs no more than 96dB? I want the most power I can source from an exhaust, and hopefully light weight as well.

Hey I thought the FMF Q2 spark arrestor was good as it has a sparky and is rated at 96dB.

What would be a good header pipe to go with this though?

powerbomb works well in conjunction with FMFQ helps lower sound even more.

new Throttle stop is cheap less than $10 US

Hi Dale

Mate,The Aussie wr400 never came with the grey wire or throttle stop.

what they do have is a very restricted exhaust muffler,just replace that with

a yz or after market one.

Check the front sprocket as some came fitted with a 15 tooth one,for ADR

'drive by' noise check(has the same effect as a throttle stop,keeps noise down.)fit a 14 tooth if req.Also fit a JD jetting kit/EKN needle will work too.

Then check out the other mods,all are very good.Made my '00 wr400 fly.:mad:

Hi Dale

Mate,The Aussie wr400 never came with the grey wire or throttle stop.

what they do have is a very restricted exhaust muffler,just replace that with

a yz or after market one.

The Canadian Aussie exhaust is not as restricted as the US version with the end cap installed.

If noise is a concern, do not use a YZ exhaust. I have found that there is not very much power to be gained (for the money) in after market pipes that will keep you at the 94 to 96 db mark. An after market header is worth the money just to be able to remove the oil filter at oil change time.

I found that doing the YZ timing on the 400 greatly improved the mid to high end power with very little affect on the low. If it's power you crave and have the open space, try it.

As stated before your bike does not require the grey wire mod and has a YZ throttle stop already installed.

When you have your carburetor off, check the throttle plate really close for signs of cracking. The plates are well known to break, and guess where the broken part goes. My engine has survived two plate breakings. I found one chunk in the muffler just about a month ago. My last throttle plate lasted about 3 years. I don't know how long the first one was in there before I bought the bike. If you need a new one call the dealer and pay between $80 and $120, or give me a buzz. I have made some stronger billet plates that should last a lot longer than the stock version.

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