Auto Decomp for 2000 WR400.

Hi all,

I have a quite new year 2000 WR400. I want to have the auto decomp mod done to it. What should I do and what parts do I need? Just a newer cam gears, must I have a pair of new cams too? I wanted a YZ426 full exhaust system too, will it fit my WR400?

Please advise, many thanks in advance.


The 400 and 426 exhaust are interchangeable. The header pipe on the later year bikes will be routed higher, but it all fits.

For the autodecomp setup you need a cam from the following:

03+ WR450

03+ YZ450

04+ YFZ 450


Get a Hotcams autodecomp exhaust cam.

It is only the exhaust cam.

You will have to reshim the valves and also buy a new gasket for the cam chain tensioner. A new cam chain tensioner may be a good idea on a high hour bike.

last thing is you can remove all the manual decomp lever and setup in the head and then replace the lever in the head with the VibeGuy plug you can get from the Thumpertalk store.

Hi Matt,

Thanks for the quick reply and help. If I just change the exhaust cam, leaving the WR400 intake cam stock, will the cam profile be the same? Any difference between a '03 YZ450 cams(exhaust and intake) setup and a pair of '03 WR450 cams?

I will try to get the pipes from a '03 YZ450 then, as you state that the mountings are the same, I like the Ti feature and looks.

Any ideas how much will a pair of used '03 YZ/WR 450 autodecomp cams be?

Thanks a lot,


I did not say 450 exhaust -- 400-426. Spend the money on a full aftermarket.

Read the YZ forums. You will see all the 450 exhaust cam post.

The 98-02 WRs and th YZs run similar header pipes. The 01-02 headers are of higer bend (clears the oil filter case) whereas the 98-00 ones are lower bend (need to be loosen when oil filter need to be removed)

The 450 pipe does not fit the 400/426 cos the exhaust port is different. The mountings are also different. Do get aftermarket pipes as they are better value for money.

On the question of auto-decomp, all you need to do is get the 03-04 YZ450F exhaust cam and fit it in. The teeth on the cams are a bit different (might cause more frequent replacement of the timing chain) but they run well on the 98-02 YZs & WRs. It makes starting a breeze and it also mellows down the power of the 98-02 yamahas (thus producing better traction and ridability).

hope I helped,

if not.... u know where to find me!


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