Airbox Flapper

Hi folks, today while removing the sidestand switch, I was curious to see how the airbox flapper works, to my surprise, it didn't!
The flapper is normally down, so it's "open", air passes without restrictions. When the ECU decides it, sends vaccum to the valve and the flapper goes up and "close" the air intake, even there's a smaller intake at the side that is alway unobstructed.
The fact is that the engine was warm, and when I started it, nothing happened with the flapper, gave it some gas on neutral, nothing. Then I thought it was speed related, so I placed the bike on a full stand, engaged a gear, but then again, nothing, no movement of the flapper. So now I don't know when it may "close" the air intake, maybe when it's cold? Who knows... Any experience/thoughts about this? At least with this short experience, I see no point on removing it.

It'll work when you're out on the road and you open the throttle wide to accelerate.
So, just when you want a heaping handful of power, the flapper slams shut and makes the engine breathe through that small inlet hole.
This is why everybody removes it and installs a fuel injection programmer - it's not there to make the bike run at it's best; it's only there to allow the bike to pass tough sound tests, and a side effect of this is reduced performance.

Snapping the throttle in the garage probably ain't gonna' activate the flapper because the conditions aren't correct.

He's right. It only works when the bike is in gear and moving. If you put your bike on a stand and put it in gear so the back wheel is turning you can watch it close as you open the throttle.

Krabill wrote:

He's right. It only works when the bike is in gear and moving. If you put your bike on a stand and put it in gear so the back wheel is turning you can watch it close as you open the throttle.

But before doing this, set up a video camera on a tripod and set the tape rolling. That way the $10K for 1st place will pay for a new bike and garage door.

LMAO, thanks for the visual Dan I could just see the bike flying off the stand and ghost riding right through the door... Although I don't know if the 10k funniest home videos would be enough to repair your pride after something like that.

The engine is not under full load when you are testing it on the stand, that is probably why the flap will not shut.

Quote :

The engine is not under full load when you are testing it on the stand, that is probably why the flap will not shut.

That's what I've thought...

It doesn't need to be under load, it just needs to be in gear. I've done it on the stand in gear and you can watch it work that way.

I've done it in gear and didn't work, anyway I've already remove it!

I just plugged the vacum hose with a screw removed the celenoid valve.

Did you notice any performance increase? Seems some have reported no difference.

I feel a little difference nothing major,

Should be a good increase , with top in and pick-up as the flapper is there to control intake noise.

Art

Removing just the flapper with an otherwise stock bike probably won't do too much for you. I had that for a while, in fact I gutted the airbox (HF style) and ran it with the stock exhaust and EXUP. Didn't notice any real improvement. The super corked up stock exhaust is to blame here. You really have to open it up on both ends to feel any difference.

+10 Add a programmer and you're ready to rip up the ground.

The world may never know the benefits of the flapper mod. I say this because I don't think anyone has done that mod last. I am in the camp of "no noticeable performance increase". However, being truly non-unique, disconnecting the flapper was the first thing I did to the bike. I fully removed it only because there were no negative effects of doing so & it removed some weight.

I fully agree with Mr. Metal's last post. So who is going to do the flapper last in order to settle this?

WRoldman wrote:

So who is going to do the flapper last in order to settle this?

I put my Mega-bomb and Q4 long before i did the Flapper/AIS/EXUP, etc...... Unfortunately, when i did do the mods i also installed a 12t upfront. So to add to the confusion. I have no idea if the flapper mod really gave a noticable performance increase.

So, people claim that the flapper closes on acceleration, correct? I don't know as I didn't have the thing long enough to even really look at it. Assuming it does close to some degree on acceleration, a test could be rather simple. Take your current setup (Q4, PowerBomb, programmer, whatever) and put a strip of duct tape across the front of the airbox inlet (assuming you still have the top piece). Don't tape up the whole thing, try a third, or maybe half of the inlet. Chances are you should notice a bit (if not more) of a performance decrease. That should simulate what the flapper does on acceleration... assuming that's how it works.

Honestly, though? Who cares? Why would you want to keep that damn flapper, solenoid, and accompanying hoses and crap under your seat anyway? I can't think of a reason NOT to remove it, even if your bike is going to remain completely stock. More (available) air is always a good thing on an EFI bike.

- A

WRoldman wrote:

The world may never know the benefits of the flapper mod. I say this because I don't think anyone has done that mod last. I am in the camp of "no noticeable performance increase". However, being truly non-unique, disconnecting the flapper was the first thing I did to the bike. I fully removed it only because there were no negative effects of doing so & it removed some weight.

I fully agree with Mr. Metal's last post. So who is going to do the flapper last in order to settle this?

If someone can tell me that if i rip it out its not going to change how lean the bike runs (i have fmf pipe but done nothing to intake yet)

I wouldn't have even put the pipe on before a fuel programmer, let alone opening up the airbox. You really should get a programmer before you do anything else.

+1 on what Krabill said. But additional note: You don't need to rip out the flapper for test purposes. It is simple to disconnect. Remove the vacuum line from the solenoid on top of the airbox. Then plug the hose by the method of you liking (i like a golf tee & zip tie).

Krabill wrote:

I wouldn't have even put the pipe on before a fuel programmer, let alone opening up the airbox. You really should get a programmer before you do anything else.

Bike came with pipe new from dealer so i havent actually modified the bike at all yet technically :P

The flapper is a noise emissions item, it will close in a certain gear at a certain speed at a certain throttle opening
It will only close when the factory want's it to so the bike will pass noise emissions, what it wont do is close at full throttle in top gear etc etc
It's very specific
Lot's of bikes have stuff like that, the last version of the R1, if you held the throttle in one spot for 10 seconds in second gear the bike would not rev up unless you changed gears, it's just a trick to make the bike legal
The flapper wont make the bike run lean or rich and it wont limit power, what it does is allow the bike to have full power 99% of the time and maybe it could decrease power slightly in very specific conditions but I cant imagine anyone feeling a loss of power If it closed at 1/2 throttle in 3rd gear @ 30mph
If anyone has access to the EPA testing regs you could reproduce it at will

I would like to know when it was actually opening and closing ... although, it makes sense to come on only to reduce noise emissions, this is a fairly quiet machine to begin with. I would have guessed it has to do more with air flow at certain speeds.

Update ....

So I did a little searching around and found this comment in an article at this New Zealand site ( http://www.motorcycletrader.co.nz/ ):

Quote :

... Pulling it apart reveals the battery and airbox side by side, with the
filter hidden behind a couple of layers of plastic shroud. In the top of
the airbox are the usual nostrils with an interesting extra – a vacuum
actuated flap. At low throttle, high vacuum, when the motor is not using
a tremendous amount of air, ie 100 kph cruise, the flap shuts off one
nostril to quiet it up. This increases rider comfort and helps it meet
Euro III drive-by noise tests. Complementing it is an EXUP-style exhaust
valve. Common to most big street bikes, it works by reducing exhaust
diameter to provide good back pressure and scavenging at low speeds, and
at high engine speeds it opens up to get good flow. Like the
self-closing nostril it also can be fiddled to ensure emissions meet
Euro test standards.

So, if they are correct, then it would appear that removing the flap would not improve any performance, but might actually reduce it. Of course if you are going to do a lot of mods, the full package, and remove EXUP, then might as well get rid of it ... however, those who are leaving the EXUP in place, it might be an adverse modification.