WR400 Exhaust on YZ400

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Jan 28, 2001
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#1
I recently bought '99 YZ400 with an FMF exhaust on it. Problem is it is way too loud for the woods. Has anyone fitted a WR exhaust(not header) on a YZ? I spoke to a cycle shop and the sales guy had his doubts about the bike running correctly. He mentioned the WR's different timing and cam, along with the fact that the WR exhaust is more restrictive and may hurt the YZ engine. Since I'm a newbie, I need all the help I can get. Would it have any negative inpacts on the YZ engine? Would I need to re-jet? If so, what size? Let me know what you all think. Thanks guys.
 
Joined
May 2, 2000
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#2
I have a wr400 and was very shocked to find how noise level and performace are very closely related. With the stock WR400 exhaust it is indeed quite, but it is also way underpowered. I mean like a choked up xr250!! No kidding, no topend ! With the FMF pipe the perfomance is problably what you would expect, but now you have the noise....... A lot of poeple like you and I have this deliema. I purchsed a supertrapp "quiet system" for mine for around $200. This exhaust allows you to adjust your noise level by adding or subtracting discs. What I have found is..... It is'nt any fun to ride until the noise starts to become unacceptable. Oh well !
FMF has a new quiet system exhast that is supposed to give you both power and low sound, but the price tag was more than I was willing to pay.

hope that helps
 

MWEISSEN

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Mi. Trail Riders
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Dec 6, 1999
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#3
I would think it would work, but you may have to rejet. Pull the anemic silencer tip and put a White Brothers Vortip or Thumper Racing insert in its place. It won't be as good as some aftermarket pipes, but will be a lot less expensive, and does OK.

If you still have the stock YZ silencer look at www.bmp.motox.org for a kit that replaces the YZ tip and gives you silencer disks to change noise (and low end response).
 
Joined
Feb 18, 2000
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#4
Hey! What happened to my post? Here's a repost of the main info: I use a U.S. Wr400 pipe on YZ426 for organised/public trail rides, dropped needle 1 notch, sized main down to next smaller that came with bike, left pilot and idle settings same, bike starts great runs fine and has never "fouled" (read carboned) a plug (leave muffler insert in, or else don't bother putting the WR pipe on, it'll be as loud as the other pipe, BUT the WR pipe is waaay heavier than the YZ pipe, but you won't notice when trail riding anyway). It will not hurt the engine. It's the opposite of jetting up for a less restrictive exhaust, and you will lose some top end, which you don't fully use when trail riding anyway.

Works great and you'll get big brownie points for being a quiet guy. You'll never get your YZ up to full revs/full throttle in the woods anyway, ok, well one time after which you'll be in the hospital, unless you're really a pro who's teasing us by pretending to be a newbie. ;)
 

MWEISSEN

Whaasssup?
Mi. Trail Riders
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#5
I want to add that the WR pipe with a White Brother Vortip DOES pass the 94db test used in Michigan for MCCCT rides. It's not as quiet as stock, but sure better than most aftermarket pipes.