flapper mod from 919.org - Wrist Twisters
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post #1 of 41 Old 08-23-2009, 04:35 AM Thread Starter
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flapper mod from 919.org

Has anyone done this mod ?919.org says it take away the power curve at around 5500rpm and make it a more linear power curve throughout the powerband.Just disconect the vacum hose from behind the air box and plug it.

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post #2 of 41 Old 08-23-2009, 07:16 AM
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That's a well known mod, costs nothing and does make a positive difference.

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post #3 of 41 Old 08-23-2009, 07:19 AM
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Lots here have.I'm not one of them.
It is a very simple mod that is free and can be undone just as quick, if it is not to your liking.

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post #4 of 41 Old 08-23-2009, 07:59 AM
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post #5 of 41 Old 08-23-2009, 08:44 AM
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Well worth spending 10 minutes to do a free mod that makes a good improvment.

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post #6 of 41 Old 08-23-2009, 06:02 PM
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I lost bottom end & "snap" and went back to stock.

It is designed to be closed until 5200 RPM to increase intake velocity which improves throttle response. It does just that, Honda engineers know what they are doing.

Just because it is making a little bit more noise does not mean that is making more power.

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post #7 of 41 Old 08-23-2009, 07:18 PM
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Quote:
Originally Posted by PAULIBIKER View Post
I lost bottom end & "snap" and went back to stock.

It is designed to be closed until 5200 RPM to increase intake velocity which improves throttle response. It does just that, Honda engineers know what they are doing.

Just because it is making a little bit more noise does not mean that is making more power.
I didn't notice a thing when I did the mod so I just left it off and plugged. Are you sure you plugged the vacuum line? Mine was no more noisy either. My guess is that about 75%+ 919 owners on here did the mod. Anybody really notice a change when it was done?

I guess I shouldn't say I didn't notice a change...I did not notice any performance gain/loss, but did find that decelerating/engine braking was smoother.

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post #8 of 41 Old 10-07-2009, 02:17 PM
 
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I know I am just a stupid person but I just took the vacuum line off my bike and it sucked! No power at all, it wouldn't even pop a wheely, there was no throttle response and it was very laggy, I pulled over and plugged it back in and pulled a wheely leaving the parking lot and had tons of power. It must give the bike way to much air on the bottom end or something. I always open up the air box up on everything I own, I like everything to get lots of air, but this mod went backwards!!! As for noise there was no difference, just a lot less power.

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post #9 of 41 Old 10-07-2009, 02:57 PM
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Quote:
Originally Posted by SMiller View Post
I know I am just a stupid person but I just took the vacuum line off my bike and it sucked! No power at all, it wouldn't even pop a wheely, there was no throttle response and it was very laggy, I pulled over and plugged it back in and pulled a wheely leaving the parking lot and had tons of power. It must give the bike way to much air on the bottom end or something. I always open up the air box up on everything I own, I like everything to get lots of air, but this mod went backwards!!! As for noise there was no difference, just a lot less power.
You did plug the vacuum line, right?


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post #10 of 41 Old 10-07-2009, 05:47 PM
 
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Yep, just as the picture showed, you can look right over the grey plastic side cover and see the line going to it. Night and day difference! I was hoping for more intake noise and power, but no noise and less low\mid power.


There was more poppy\burble on deceleration, not much but did sound good!

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post #11 of 41 Old 10-07-2009, 11:11 PM
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.... well i did it to mine (it was the very first of the few mods i've done so far) ... mine seems to run a lil smoother with it done to mine i'd say .... maybe i'll switch it back again here for a day again just to see if it really DID run that much smoother ...

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post #12 of 41 Old 10-08-2009, 01:52 AM
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I'm not exactly sure if this goes for the 919.

But when I had the RC51, the flapper mod was a popular thing to do also. One reason for having the flapper on the RC51, at least to the forum members on that bike, was to meet noise levels.

Now it did make a much more linear feel on the power. Also made the intake WAY louder, with a cool whirling noise. Of course the RC51 breathes a lot heavier than the 919 and is fitted with dual filters from a ram air design.

I'm guessing the best way get a conclusion on the flapper mod is to do a couple of runs on a dyno. Maybe next time someone gets their PC3 tuned? Anyone...?

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post #13 of 41 Old 10-08-2009, 06:21 AM
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Quote:
Originally Posted by SMiller View Post
I know I am just a stupid person but I just took the vacuum line off my bike and it sucked! No power at all, it wouldn't even pop a wheely, there was no throttle response and it was very laggy, I pulled over and plugged it back in and pulled a wheely leaving the parking lot and had tons of power. It must give the bike way to much air on the bottom end or something. I always open up the air box up on everything I own, I like everything to get lots of air, but this mod went backwards!!! As for noise there was no difference, just a lot less power.
Quote:
Originally Posted by SMiller View Post
Yep, just as the picture showed, you can look right over the grey plastic side cover and see the line going to it. Night and day difference! I was hoping for more intake noise and power, but no noise and less low\mid power.


There was more poppy\burble on deceleration, not much but did sound good!

I'm not sure what, but you did something wrong. When you disconnect the vacume line from the Variable Air Intake Control System, it's the hose (vacume line) that needs to be pluged. Did you maybe plug the diaphragm instead? An open vacume line would have cause the symptom you described.

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post #14 of 41 Old 10-08-2009, 08:39 AM
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like people have stated the flapper mod is super easy and will produce a more linear power with more bottom. I did it on mine and love the added intake sound, and so much more linear power curve. Before you would go WOT in first off the line and the front tire would stay on the ground and all the sudden come off at like 5600 rpms.... now the front tire starts to float off the ground at like 3k!

The people who say they loose power because of it are wrong, your gaining power in the bottom and thus no longer have the jump in power at 5200 rpms + due to the flapper opening because its already open. And to those who say the flapper is there to increase are velocity are wrong... the air goes in hits the air filter and gets completely slowed down.

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post #15 of 41 Old 10-08-2009, 08:51 AM
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Maybe I'm missing something, but it seems that the basics of how this works is escaping people. The valve is activated by vacuum. At idle and when accelerating, there is very little or no vacuum. Please read this for a very through explaination...Manifold vacuum - Wikipedia, the free encyclopedia

The valve is normally open fully. Thusly, the variable air intake control valve will only close (restricting air to the airbox) when a moderate to strong vacuum is applied. This would occur only on deceleration right? If the bike doesn't have enough vacuum to close the valve at idle with the neutral switch disabled, then how can it pull a stronger vacuum with the throttle opened (even a fraction) while cruising down the road?

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post #16 of 41 Old 10-08-2009, 10:10 AM
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I was called out on this just the other day actually, there is a vacuum canister and solenoid that operates the flapper it doesn't come directly from the manifold.

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post #17 of 41 Old 10-08-2009, 10:29 AM
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Quote:
Originally Posted by cmurphy84 View Post
Maybe I'm missing something, but it seems that the basics of how this works is escaping people. The valve is activated by vacuum. At idle and when accelerating, there is very little or no vacuum. Please read this for a very through explaination...Manifold vacuum - Wikipedia, the free encyclopedia

The valve is normally open fully. Thusly, the variable air intake control valve will only close (restricting air to the airbox) when a moderate to strong vacuum is applied. This would occur only on deceleration right? If the bike doesn't have enough vacuum to close the valve at idle with the neutral switch disabled, then how can it pull a stronger vacuum with the throttle opened (even a fraction) while cruising down the road?
Quote:
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I was called out on this just the other day actually, there is a vacuum canister and solenoid that operates the flapper it doesn't come directly from the manifold.
yup... there is a lil vacuum storage canister and solenoid that controls the flapper.... i got the service manual... id be more than happy to post up pics of the flapper vacum diagram, and the honda service manual saying that its closed below 5200 rpms and open above 5200 rpms.

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post #18 of 41 Old 10-08-2009, 10:41 AM
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Well...looks like I was missing something. Carry on.

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post #19 of 41 Old 10-08-2009, 11:13 AM
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i did this mod as well. i took the whole flapper piece out of the intake and duct taped over the hole. plugged the hose and went for a ride. nice and smooth power. the only way you hear the extra growl is to open it up full throttle at around 2500-3k rpm and than you will hear it. im sure it helps to remove the entire flapper too.

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post #20 of 41 Old 10-08-2009, 12:28 PM
 
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I did not plug the vacuum hose, someone on here said you didn't have to, so if I plug the hose when I take it off then will it run good? Taking the hose off without plugging it hurt the bottom end power big time!

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post #21 of 41 Old 10-08-2009, 12:57 PM
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ya you need to plug up the hose you took off... you can put a golf tee in it or fold it over on itself and use some zip ties.... of best of all by a lil screw tip cap from your hadware store and slip it over the vacuum line

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post #22 of 41 Old 10-08-2009, 11:07 PM
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Quote:
Originally Posted by cmurphy84 View Post
Well...looks like I was missing something. Carry on.
yeah... don't worry, I was the jackass a week or so ago... and yes to the other guy you need to plug the vacuum leak. not sure that it'd really cause much effect on the bottom end as how and when the vacuum source works, but its still good policy

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post #23 of 41 Old 10-09-2009, 08:51 AM
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Quote:
Originally Posted by PAULIBIKER View Post
I lost bottom end & "snap" and went back to stock.

It is designed to be closed until 5200 RPM to increase intake velocity which improves throttle response. It does just that, Honda engineers know what they are doing.

Just because it is making a little bit more noise does not mean that is making more power.

It does make more power... A nominal amount, but consistently 1-2 hp gains are seen in the midrange on the dyno.

The theory of increasing intake velocity is sound (no pun intended), but it's also negligible in the scope of these motorcycles. If it really worked as prescribed then every factory racebike in the paddock would be fitted with flapper valves to get the absolute best response & power out of them and the truth is not one factory race bike has a flapper valve system on it in the induction side or the exhaust for that matter.

They put these on street bikes for noise abatement plain & simple. Most of the bikes that the EPA has failed for noise testing in the last decade have been for intake and/or valvetrain noise rather than exhaust.

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post #24 of 41 Old 10-09-2009, 08:53 AM
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Quote:
Originally Posted by Lord Duckhunter View Post
It does make more power... A nominal amount, but consistently 1-2 hp gains are seen in the midrange on the dyno.

The theory of increasing intake velocity is sound (no pun intended), but it's also negligible in the scope of these motorcycles. If it really worked as prescribed then every factory racebike in the paddock would be fitted with flapper valves to get the absolute best response & power out of them and the truth is not one factory race bike has a flapper valve system on it in the induction side or the exhaust for that matter.

They put these on street bikes for noise abatement plain & simple. Most of the bikes that the EPA has failed for noise testing in the last decade have been for intake and/or valvetrain noise rather than exhaust.
And that would seem to be the definitive final word, thanks LDH!

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post #25 of 41 Old 10-09-2009, 11:13 AM
 
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So by plugging the hose it will make a difference?

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post #26 of 41 Old 10-09-2009, 11:37 AM
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If you don't plug the hose AS THE INSTRUCTIONS CLEARLY STATE then you end up sucking fresh air into the throttle bodies which is never a good thing unless it is properly metered & mixed with fuel

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post #27 of 41 Old 10-10-2009, 03:15 AM
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33 degrees tonight. I think I am going to see if this works about - say April...

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post #28 of 41 Old 10-10-2009, 08:44 AM
 
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Well if I don't plug it and it sucks unmetered air then maybe it will lean the motor out and get rid of the exhaust stink, lol, wouldn't it have more power if it was leaning the motor out a little? And that is a very little hose to suck air through, I can't ponder it making much of a difference.

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post #29 of 41 Old 10-12-2009, 08:09 AM
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Quote:
Originally Posted by SMiller View Post
Well if I don't plug it and it sucks unmetered air then maybe it will lean the motor out and get rid of the exhaust stink, lol, wouldn't it have more power if it was leaning the motor out a little? And that is a very little hose to suck air through, I can't ponder it making much of a difference.

That's why I am the guy that started the mod and has the dyno for testing & you are the one still asking the questions

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post #30 of 41 Old 10-12-2009, 11:05 AM
 
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Well I unplugged it again and stuck a .22 long bullet into the hose, perfect fit! After putting some miles on it, it does seem to have more mid range, seems like a 4000 rpm roll on is much stronger, but again the low end power doesn't seem to be as strong, doesn't seem to be the big wheely popper as before. I am happy to get rid of a little low end bucking and jerking. Thanks for all the replys!

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post #31 of 41 Old 10-12-2009, 11:25 AM
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so how much heat can a 22 LR round handle before it goes pop?

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post #32 of 41 Old 10-12-2009, 11:33 AM
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this thread makes my head hurt. Waiting for headline motorcyclist shot in junk while riding.

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post #33 of 41 Old 10-12-2009, 11:57 AM
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He said bullet, not cartridge. Why he didn't use a casing I don't know... it would weigh less at least.

Those are rimfire too, so I'd hope he didn't put an actual round in the hose - what if it bounced off something? On the upside, it would just make a loud pop as the bullet and the case separated, hopefully not damaging to much in the process. It's going to blow the line apart regardless, but without the bolt holding the bullet in the chamber and a barrel of some sort the bullet is just going to "pop" out of the casing. It /PROBABLY/ wouldn't damage much, but I'm not willing to try it...

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post #34 of 41 Old 10-12-2009, 03:17 PM
 
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I guess I should have said cartridge, I kinda figured that everyone would pick up on that, live ammo goes into the chamber...


Again though perfect fit!

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post #35 of 41 Old 10-12-2009, 05:29 PM
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Please don't expose any mechanic to your live ammunition exactly where he doesn't expect it to be. I don't imagine it would be easy to make a rimfire round go off by pulling on it with a pair of pliers, but it probably wouldn't be impossible.

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post #36 of 41 Old 10-12-2009, 06:59 PM
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Did flapper mod, went back to stock configuration, no performance gain with mod. Think I'm getting better mileage stock.

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post #37 of 41 Old 10-12-2009, 07:22 PM
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Quote:
Originally Posted by lmtdgov View Post
so how much heat can a 22 LR round handle before it goes pop?
Not sure, but I know a campfire works.....

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post #38 of 41 Old 10-12-2009, 07:43 PM
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Quote:
Originally Posted by Brett View Post
Did flapper mod, went back to stock configuration, no performance gain with mod. Think I'm getting better mileage stock.
After changing those god ugly mirrors with the Aprilia mirrors
(thanks to the OP on that tip) I put on 3,ooo miles and out yesterday I stopped
to take some pictures.I decided to take that vacume hose off and pluged it with a small branch.
All I can say is I wish I did it 3,000 miles ago.It's starting to resemble a motorcycle now.
It's funny to read the different reactions to this 5 min.mod.

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post #39 of 41 Old 11-12-2009, 10:05 AM
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Hi!
Is there difference between U.S. and Europe's 919's when doing that mod? Im in Europe and have a euro 9nineteen.

Thx

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post #40 of 41 Old 11-12-2009, 10:13 AM
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