WR400 Exhaust on YZ400

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 thumper 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.

Once again the "knowledgable" have confirmed why TT is a great asset to us. The exhaust systems are completly interchangable and you may have to do some jetting (possibly down on the pilot and main, as well as raising the clip)

Change the pipe, ride it and find out. Nothing catastrophic will happen. There have been several people here that have put the WR pipe on a YZ. I traded my dub-R pipe to a YZ guy, for his YZ pipe.


99 WR400f, YZ timed, MX-Tech suspension, Scotts steering damper, White Bros E-Series (12 discs), tapered header and a/f. Kouba T-handle for the fuel screw. Works Connection billet throttle tube and frame guards. Cycra Pro-Bend, triple clamp mount handguards. Thumper Racing rad guards, Renthal Jimmy Button highs, YZ Tank and IMS seat, YZ number plate, odo removed, EKP #4, 50PJ, 175MJ at 500-1000' Thanks James Dean!

we just did this to my buddies bike on sunday. I have theWR and he bought a YZ. But with the fire danger where i live (north Idaho 2500' ) he needed a spark arrestor. So i gave him my old pipe to put on. We took out the baffel of course. He said it calmed the bike down a little but it still hit hard but not quite as hard. Not we are just going to go on full day ride so he can see how he likes it. it is still loud but nothing compared to the YZ pipe. I will let everyone know how it works out. Oh yea we did nothing to the jets.

I use a U.S. WR400 muffler on my YZ426 for organised trail riding. I leaned the jetting: one size down on the main and drop the needle one notch. Runs perfect. It's the opposite of jetting up for a higher flow exhaust. You lose some top end, but become stealth quiet in tradeoff. I've never fouled the plug either, left the idle etc bone stock and it always starts easy too. If you're a performance fan, be aware the WR pipe is waaaay heavier, but for trail riding you'll never notice. What a great bike! Only bad thing was swapping in the 01 clutch plate to fix the grabbing.

Thanks for the info guys. I was able to bolt the exhaust right on and it runs much quieter. I haven't had a chance to ride it(just up and down my street).

Thanks again.


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