Going back to stock myffler?

I'm going to try the stock muffler for kicks.
Bought this bike with an aftermarket pipe installed.
Do I need to do something with the EXUP dealie?
I do have the EXUP valve actuator.
Can I eliminate the valve on the pipe somehow?

Please advise...

More important than the exup is the AIS. My understanding is that if you run the stock muffler with the AIS removed you can damage the catalytic converter.

Many folks have just cut the butterfly out of the EXUP if they wanted to run the stock pipe sans flapper thingy and actuator.

....vas iss AIS...?

Use the search feature.



click me 1

click me 2

click me 3

...well alrighty, that's been done on my bike.
Question was, what do you do/with the EXUP gizmo on the actual muffler?
Anything?
Nothing?
I haven't had a chance to look at it yet...

Isn't the valve open by default?

I think the servo does nothing but close it.

At the very least just secure it in the full open position.

I don't have a clue as I haven't looked at it. Just got it in the mail.
I figured one would probably wire it open but thought I'd ask those that are in the know.
Thanks.

I just checked mine. There's a spring mechanism that holds the valve in it's full open position.

Would be easy to wire so it won't move, but even without wire, the spring will hold it open.

...gratsi mejefe'. Now I know what I have to do...besides get the Yosh pipe off.
It's kinda on there real good.

motokid wrote:

Isn't the valve open by default?

I think the servo does nothing but close it.

EXUP Type valves I've seen are closed at off and low revs - by default. The servo cranks them open at higher revs. According to the service manual cycling the valve through the diagnostics test opens it then re-closes. Doing this on my bike means it is closed by default. I'll defer to anyone who has removed the pipe and actually looked. The spring may default to an open position - don't know. Someone grab a hacksaw and post up pics. I hate not knowing everything.

From the manual, pg 8-40;

"53 EXUP servo motor
Turn the servo motor once in the
open direction and then in the
close direction.
Illuminates the engine trouble
warning light."

A couple more observations....

MTB's EXUP video. Watching the valve stay in what I'm thinking is the closed position kind of makes sense. It sounds like he never revs it past 5-6k rpm but still I expected it to open more and made me think either his ECU is messed up or the calibration on the valve or cables was off or 250cc of exhaust didn't mind being choked that much. Or - Yamaha had a noise regulation issue and programmed it to not open until much later.

Racing with EXUP. I ran a Leo V can on my Daytona 675 and kept the exhaust valve. I'd take a hit on a straight longer than 1/4 mile but have an advantage out of the turn. Wasn't by choice but budget. Damn if I could afford the full titanium Arrow system. The 675 (like an R1) would cycle the valve upon turning the ignition on (like the WR diagnostic chk). My 675 would kick it open incrementally starting about 4500 rpm. So the valve really only would be used on a race start - which made me dream I'd become a millionaire by inventing a lightweight disintegrating one shot exhaust valve membrane just for starts and selling it to anyone that wanted to get a hole shot on Pedrosa.

My thinking is that an exhaust valve is a great tool for a street or trail bike, but I'm questioning the design integrity of the WR250R/X unit.

motokid wrote:

I just checked mine. There's a spring mechanism that holds the valve in it's full open position.

Would be easy to wire so it won't move, but even without wire, the spring will hold it open.

First of all I did check mine. Physically held it in my hands and looked into pipe. When there are no cables connected to the EXUP valve the spring mechanism holds the valve at full open position.

Now, go look at this thread again.

Notice the picture MTB took second post in.

See the close-up of the exup? See the tab of black metal right on top that is resting against a silver metal stop?
That's the stop for the spring tension mechanism. It's fully open. Fully against stop.

Now go watch the video. You can see that black metal tab and the stop it rests against. The tab hardly ever moves off that stop.

The EXUP valve is fully open almost all of the time in MTB's video.


If you STILL question what the phuck is going on, PLEASE get some video of your EXUP valve in action.

Not of one on a CBR1000.
Not of one on an R1 or R6.
Not something you've nicked off the interwebz.

Get some video of the EXUP on your wr250x/r, or a buddy's, while the bike is being put through it's paces and post it in a new thread.

Go take a few close-up pictures of the EXUP valve and post them. With the bike off that valve is wide open. Why wouldn't it be?


Speculation and theory is fast becoming like a religious debate. That thread can be found in the "off topic" section.


I'll stand by MTB's video until somebody else posts something of at least equal relevance.
Until then, MTB's video is proof enough for me that the Yamaha EXUP system on the wr250x/r is basically worthless weight.

The WR-250R and WR-250X EXUP valve doesn't work like the EXUP valves first seen on the Yamaha sport bikes like the 1989 FRZ-1000W, 1994 YZF-750RF, and then the 1998 YZF-R1K.
Those did stay closed (not 100% closed, but close enough) at low RPM and opened as the revs rose.
The valve worked like a guillotine moving up and down and was positioned at the end of the header pipes.
Those EXUP valves were supposed to fool the bike into thinking it had both long exhaust pipes for low-end torque and short exhaust pipes for top end power at the same time.
An added bonus was that it made the bike a bit quieter.

The one on the WR-250R and WR-250X act like ones on current sport bikes that have a butterfly valve back in the exhaust, just before the muffler.
It's open until the electronics make it close to a certain point and then open to a certain point under certain conditions.
I believe it's now mainly there to reduce noise under certain conditions with any additional low-end torque produced as secondary.

Well installed the stock pipe yesterday. The valve definitely is in the open position with a fairly heavy spring.
It's nice and quiet now. I'd say there's about a 2hp seat of the pants change in overall power and a bit of lacking snappiness that I had with the Yosh pipe. I can definitely hear the airbox now.
Trade-offs...
Anyhow, a bit more riding will make the final decision, but I'll probably warm up to the stock option.

Don't powercommanders have the ability to control an external circuit? Maybe a smart person could program a map that would run the valve in a more performance minded manner (closed at low rpm for torque, open at high revs for good power)

freetors wrote:

Don't powercommanders have the ability to control an external circuit? Maybe a smart person could program a map that would run the valve in a more performance minded manner (closed at low rpm for torque, open at high revs for good power)

Why use a power commander with a stock muffler?

Motokid and all, thanks for the well considered replies.

But...

Here's the deal; The EXUP should be closed at low revs to create higher torque. I think we can all agree on that. So if what Motokid is saying is correct, the WR250R/X EXUP is indeed a waste of weight and useless. If his referred to thread photo is the open position then in the MTB video the valve only seems to partially operate (close) when he's accelerating hard at low revs at upshifts. Makes sense, but its hardly working even at that.

So did Yamaha engineering screw up and the 250cc motor is just too small to benefit from one? Is the ECU programming kack or its a budget unit? If done properly an exhaust valve should make a real difference in low end performance, ie; torque.

There has been a lot of mention of the valve only being installed for noise regulations. Well, if its not even closing you can throw that argument in the bin.

And Motokid... Sorry if I offended you. Just trying to figure this out.

No offense at all.

It's frustrating because there's so much speculation.

Tomorrow, when it's daylight, I can take some pictures of my pipe and EXUP.
Now granted, mine is not on the bike. But you can easily see the valve and it's open position.

Then it's up to somebody else to post pictures of it in stock trim on the bike.

motokid wrote:

Why use a power commander with a stock muffler?

To run your bike at a proper air/fuel ratio instead of the crap Yamaha has programmed in due to the enviro nazis.

WRXer wrote:

motokid wrote:

Why use a power commander with a stock muffler?

To run your bike at a proper air/fuel ratio instead of the crap Yamaha has programmed in due to the enviro nazis.

Having the bike all corked up with the stock exhaust, and then making it run richer by adding fuel isn't really going to make anything better.

The stock configuration can be run for tens-of-thousands of miles. The general "myth" that people report is that Yamaha tunes things a touch on the lean side.
"Leaner is meaner" is something that goes back many decades.

But if you want to force more fuel through the system you're more than welcome to do it.

I just don't see any benefit to doing that when everything else is stock.

I think Yamaha got the ratios right for a fully stock set-up.
It's only when you mod things that additional fuel is thought to be needed.

I ride the bike with a pc5 and the stock muffler, and a powerbomb, too: think i have much more low-end-power with the stock muffler (without exup), than with an aftermarket muffler...

Now i want to remove the whole exup- v.- have anyone an idia how to work: if i remove the v. in the pipe (dont know how to remove it-without cutting the pipe), i have a big hole in it (where its connected to the cables). How could i close this hole: maybe with a bolt or welding??
Have anyone reoved the complete exup

motokid wrote:

WRXer wrote:

motokid wrote:

Why use a power commander with a stock muffler?

To run your bike at a proper air/fuel ratio instead of the crap Yamaha has programmed in due to the enviro nazis.

Having the bike all corked up with the stock exhaust, and then making it run richer by adding fuel isn't really going to make anything better.

The stock configuration can be run for tens-of-thousands of miles. The general "myth" that people report is that Yamaha tunes things a touch on the lean side.
"Leaner is meaner" is something that goes back many decades.

But if you want to force more fuel through the system you're more than welcome to do it.

I just don't see any benefit to doing that when everything else is stock.

I think Yamaha got the ratios right for a fully stock set-up.
It's only when you mod things that additional fuel is thought to be needed.

Scary. LEANER IS NOT MEANER! Otimum power is as low as 12.8 A/F ratio. Who cares if the stock exhaust is "plugged up" for the air it is flowing its still lean. Not all bikes are lean, THIS ONE IS. Further, look beyond a peak dyno number. A proper map is more about smoothness & throttle response anyway. Glad you are happy with the low hanging fruit; many are.

AFAIK, All stock bikes are tuned lean for EPA, CARB and EURO regs CO and sound measurements. My R2 has EXUP and the stock pipe with an FMF programmer. Not as important for me as I'm at 5000' ASL where if you take the table percentage adjustments for jetting I come out almost perfect for a piped and airbox modded motor but the programmer allows fixing the common lean dip around 3-4k RPM, eliminating acceleration stumbles and general fine tuning. The whole thing would sure be a lot easier if Harbor Freight sold a cheap drop-it-down-the-tailpipe AFR gauge.

How does the power feel after going back to stock?

...about 2 HP down...