Quiet Exhaust-And Wheelies Too!

There has been a lot of talk on quiet exhausts lately. While the closed courses I run have neighbors FAR away, there are a few trails nearby homes so a quiet pipe is the only way to keep peace. The battle between low noise and HP continues.

First, let me say I wasn't expecting much with this mod, but pleanantly was surprised. I expected a serious lack of power :)

Using a stock YZ pipe, a $1.47 metal 1.5" utility sink drainplug from Home Depot, and a hammer :D, I popped the sink plug (has many small opening) in the tailpipe. It allows estimated 55-65% flow by visual inspection.

First, I decided to run my current jetting for a test run. EKP#4, 170MJ, 48PJ, 100MAJ, untouched AP, YZ timing, '00 WR, WB tapered header--600ft, 70 deg F.

I ended up not changing it due to mud buildup. Wanted to change it out to a EKR, and perhaps 165MJ, but didn't want to risk getting crap in the carb.

Anyway, the bike ran GREAT! MUCHO quieter, there was no comparison. Yes, the power was a little soft, but it felt like bottom was just as good, it just didn't rev so violently. Didn't foul a plug, or show any signs the jetting was really that bad. That surprised me a little, too!

Overall the power wasn't that bad given the conditions. My rear end wasn't sliding out as much due to wheelspin following terrain. Basically was going just as fast as always though this trail.

My 'WR was pretty pumped up before, and now it's just a little more tractable. A few times I could swear the bottom was actually better, as evidenced by wheelie ability. It felt like more power than I expected to have when corked the pipe up.

I didn't really get a chance to ring the motor up too hard due to conditions. But the delivery was smoother. It felt like WR timing with an open pipe and aggressive needle.

James, Taffy hopefully you guys read this.

You remember about a month ago I was going to try the new jetting specs you recommended. Well, due to the nasty mud around here this time of year, I want to hold off on wicking the power up until it dries out over the summer. Right now a smoother delivery is what I need. I do wish to hear what your thoughts are on jetting with the modified pipe.

Any YZ pipe owners may as well give this a try for either cheap noise reduction or smoother delivery for mud. It's only $1.50, and maybe some leaner jets. Check out your plumbing shop!

Interesting, did I tell you I have a stock YZ pipe now?



97 KDX220, 86 TTR225, 99 WR400f, WR timing, throttle stop trimmed, air box lid removed, White Bros head pipe, silencer and air filter. De-octopussed. Works frame guards and Thumper Rad Guards, Scotts steering damper. Odometer and headlight removed. Cycra Pro-Bend hand and mud guards. YZ stock tank, IMS seat and number plate. Renthal Jimmy Button "highs" and Renthal Soft half waffle grips. AMA, SETRA, Happy Ramblers MXC, Rausch Creek MXC, Tower City Trail Riders.

[This message has been edited by Bill (edited 04-23-2001).]

what year is that sink plug, i hear they had a lot of trouble with 96'ers!!!



The donor bike is a 98 and my WR is a 99.


Originally posted by Bill:

Did I tell you I have a stcok YZ pipe now?

What year YZ, Bill?


Taffy- You crack me up!

You may want to try Larry Roessler's STROKER Quiet Tip. It's aluminium, has a greasable rubber O-ring, mounts or comes off in less than a minute with one bolt. It delivers performance without excessive sound.

It fits the stock WR-400,426 silencer.


I did the same thing 2 weeks ago and i confirm mcarp's

description on the effect on the engine power (smooth, tractability ...)

My dealer sels metal rings 1,5 cm (?????inch) wide with diameter for a YZ exhaust with a perforated plate welded on each side (if it's too restricted i just remove 1 side).

Cheap, works great, and when riding in MX you can easily remove it.

I'll try to send some pictures next week.


'99 WR400 F, YZ exhaust, throttle stop trimmed, WR timing, airbox cover removed


I aggree with your observations. I sometimes use a stainless screen cut from an old spark arrestor with a similar restriction on my '99 YZ exhaust. It is quieter and feels like an increase in low-mid end torque. The top end loses some power but the bike is MUCH quieter and very tractable.

The jetting stays close to the same, with the restrictive exhaust running slightly richer. I would change the clip to EKP#3 rather than using the EKR and stay with the #170. (Or leave it alone and be happy both ways :) )


Anyone has an idea (or has measured) the db sound level with such a restrictor on a YZ exhaust ?




'99 WR400 F, YZ exhaust, throttle stop trimmed, WR timing, airbox cover removed

I had the same observation with my setup compared to stock. I Have a complete megamax 2 pipe with only 6 disk and the quiet core. I don't have to say that the bike is almost as quiet as stock but with my 15//45 gearing, I can put whellie at will in second gear and in third gear by playing with closing/opening the throttle.

A friend of mine tried my stock brother's bike and he was always stalling in trails. He tried my bike after and he wasn't stalling anymore. This should be explaining why people don't understand how I can do tight trail riding with that gearing without any stalling problem and without playing with the clutch.

Furthermore I didn't see a big lost in low end torque by going to the yz timing.

Hey all.

I have been thinking about this YZ stock pipe thing for awhile now. Infact I ended up with 2 silencers, 99 and 01, and an 01 stock head pipe. I've even found some perfect stainless wire mesh for a spark arrestor. Now the problem.

I went ahead and drilled out the rivets and took the end cap off. Because of the the way the core and the end cap meet there seems to be no way to put the mesh in. I guess I could weld it in but I would rather not. Any suggestions?


[This message has been edited by JJ (edited 04-25-2001).]

Well I've been able to ride twice now in dry conditions with the exhaust plug. The transition from low to mid range is MUCH slower than it used to be. Once it hits, no problem with power, yet the instant snap is gone :) Something that works so grand for mud just doesn't cut it.

So I took a cutoff wheel and punched a hole in this bad bay. Louder? yes, but not much. Power was better yet, but still had sluggish repsonse when I banged it open. It wasn't quite as bad, bad wanted more instant response for those unpredictable obstacles. Still using original jetting posted, may have something to do with it.

The way low end off idle was better than without the plug now. Stalling was not a problem while crawling between trees and up river banks

I think my conclusion is I'll use it for the wet trails for spring/fall or when I need to be sensitive as to how much noise I'm making, then remove it for the track or uninhabited riding areas.

Next step is to buy another, punch out a bigger hole and see what happens. I'm willing to sacrifice a little power for lower noise, but the "full monty" plug was too much. Perhaps my jetting was partially to blame as I failed to change anything (yet).

The Search continues!!!

Yes-the search continues. Great post. Thanks, P

Well, I've been able to ride about 6 times now with the homemade exhaust insert.

Jetting with this restrictor has been a little tough. Part of that is riding in two states, with different elevations, oxygen content (read TREES!!), temperature, and humidity (cold, dewy mornings, hot afternoon). Also changed back to stock airfilter for a few rides-too lazy to clean the WB's.

Anyway, I believe I have came to a conclusion that perhaps a few folks can "live with". Or perhaps one that is better yet.

As you recall, I took a $1.50 plumbing restrictor, and shoved it in a stock '00 YZ pipe. YZ timing, '00WR jetted ala James Dean (thanks again, James).

--Using full restriction of this unit, sound level was dramatically reduced everywhere. Idle was extremely quiet. Estimate this to be slightly louder than a WR pipe with the insert, perhaps more so on the upper revs.

Power was overall good great in the slick terrain. Bottom end seemed smoother to transition to the mid hit. Just odd idle seemed to chug stronger than ever, I wasn't worrying about stalling so much. Gentle throttle and little wheelspin made the WR climb trails where the 2-smokers where having trouble. BUT!!!! I felt there was hesitation when the dirt dried up and was able to really able to hammer the throttle. I had to anticipate a little more in advance that I wanted the front tire to come up, you know to clear logs or CR80's :). It wasn't terrible, but I can see where this can be a problem.

--Cut out inside .75" of restrictor. Now you're talking! A little louder, but not too bad! No where near a stock YZ pipe at idle, low end or midrange. When really screaming it out, it was louder than the full restriction for sure. It didn't have that nasty "bark" until I screamed it. Instead "putting around" hehe the bike was quiet. The power was better, the response problem went away.

It didn't want to wheelie in 4th as easily as with no restrictor. I rode in 4th gear for about 6 miles straight on a dirt road, from bogging and clutch slipping to screaming it out and pounding 5th. Wheelies weren't doable everytime.

1,2,3 gears were fine, all the power I wanted.

--No restrictor (stock YZ pipe). Surprisingly didn't perform THAT MUCH better than the middle ground above. It only showed it's colors in the high end where it would wheelie in 4th more consistently. Also, it seemed just a little more violent if I was able to hold the throttle open for 4-5 seconds. (normally I can't that where I ride, but this one meadow was begging for it) The noise was back!

I asked a friend to help me compare the noise levels. His judgement was from hearing all 3 setups anywhere from 2 yards to about 3,000 feet away. He could still hear all except full restrictor at appx 4,000 feet away. This was over two hills and long rolling meadow! He couldn't hear me shout, but could hear my bike!!! Granted where we were in WVA the sound travels forever over the hills, but that's probably typical of where many of us go riding (at least in the east)

So, I've had decent results with the "middleground" at least for my homemade restrictor.

I would like to post of pic of this thing, but I don't have a site to host it on. Anyone care to post this for me?

Happy trails,


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