Where does the fuel tank air vent hose route to once it ducks into the engine bay?

Hey guys -

Im having an issue where my gas tanks vacuum seals itself shut after driving for 30-50 miles. It slowly kills my driving experience, idle goes down, starts to stall and sputter, etc....

I lifted the tank up to see if there was an obvious kink in the hose (I just had the valve clearance checked at the dealer so I thought maybe they kinked or pinched it) but everything looked OK from immediately under the tank.

I can't really see where the hose goes to once it dips into the frame and engine area. Anyone have good pictures? The service manual didnt have much.

Is this hose easy to replace? Is it easy to test? Can I just unplug it from the bottom of the tank and blow in it? Or is it more involved?

Appreciate any help.

--- EDIT ---

Im adding pictures after my afternoon tests.

There are two hoses under the gas tanks located towards the headlights. One is the fuel overflow drain tube. This one I can blow through just fine (from the hose to the ground).

The second is the smaller tube I cannot suck in (from the where ever it start into the tank). I can however blow out small amounts of air, it sort of gurgles and does not flow freely. What is this hose?? I think this is my culprit for the tank not equalizing pressure?

This smaller tube tucks in behind the frame and T's off in two directions. Where does this go and what does it do?? (pic 2)

Any help is appreciated.

 

Added new pictures and testing info..... help! Gas tank cant breathe!

 

Here is a very bad pic... Page 1-44 of the honda manual

 

Thanks! Should the evap canister allow air both directions (into and out of the gas tank)? It appears from the picture that it should only allow flow outbound from the gas tank.

If that is the case, how does the gas tank equalize pressure when fuel is removed? How does it add air back in?

 

I don't know for sure but it would have to. That may be what the open to outside air port on the evap canister is for.

 

Just a guess, but are you in the habit of filling the tank all the way up to or into the neck? If so you may have liquid fuel in the evap canister.

 

No but it did recently get knocked over.

Im going to see if I can just remove the thing. Is there an easy way to get to the solenoid and 'T' where the hose comes off the gas tank? Will I get access if I remove the airbox? (any how-tos on here? I searched and found a couple good posts but no walk throughs)

 

Click on this link and read carefully Judobrian. Click me.>>>>>http://vfrworld.com/forums/6th-generation-2002-2009/40584-pair-removeable-help-w-pics.html

If you have any questions just PM me and I'll walk you through.

 

Stosh - First off your bike is insane. The painted frame work is amazing, and the fact that you have different color screws for your gas cap makes me happy! Nice work!

So I got the evap canister off tonight, but I have a few questions. The line from the evap canister did not run straight to the gas tank. There was a 'mystery canister' that was under the handle bars/frame that it ran to. (see pics).

Also the line that ran from the tank did not go straight to the evap canister, it ran under the frame rails into a 'T' of some sort. Any ideas what is going on here?

I removed the evap, and ran a new line from the tank to the bottom of the bike to get fresh ai (equalize pressure). Am I good to go? Or do I need to worry about those other parts?

Side view evap can and lines...



More detail from same view


This is the 'mystery canister'. Picture taken from under the bike looking up, right under handle bars tree.


This is the same 'mystery can' from the side of the bike, looking through the passenger side radiator.

 

Nope that's definitely not right.

Those two hoses were connected incorrectly on your bike Brian. Here's a pic of the vacuum hose routing diagram decal that should be stuck right on top of your airbox lid.

It clearly shows that there are two hoses that connect to the EVAP canister on the right side of the bike. The tank breather hose (Green arrow) goes directly to the breather port on the underside of the gas tank,and the other hose (Red arrow) goes directly to the purge control solenoid that's bolted onto the frame rail under the right side fairing panel.

That 'mystery canister' is actually a vacuum chamber. It's used to store vacuum to operate the variable intake valve. (which is more commonly known as the flapper valve,part number 8)

The vacuum chamber is part number 10 in this pic.

Since you didn't have a pic of this I'm going to hazard a guess that the 'T' you mentioned is possibly part number 13 in the pic above. :unsure:

If the tank breather hose was connected there then that would definitely make your tank vacuum lock because the port on that valve is under vacuum.

Yep,I've got a pretty good idea of exactly what's going on here Brian.

In your first post you mentioned that you just had your valves checked by the dealer. It's a whole lot easier to do the valve clearance checks with the gas tank removed,which is what I'm guessing the mechanic probably did.

Somewhere along the way he must have removed those vacuum hoses and when it came time to reattach them he didn't have a clue as to where they were supposed to be reconnected.

So instead of simply looking at the vacuum hose routing diagram decal and verifying their correct routing positions before he connected them I'm betting what he did was close his eyes,pointed at your bike,started twirling his finger in the air and said "Eenie meenie miney moe where da fock does this hose go". And when he opened his eyes wherever his finger was pointing to that's where he connected the hose. :lol:

Sorry,that's harsh I know but it's probably exactly what happened.:sorry:

Yep.

Just cable tie that tank breather hose loosely to the frame rail so it doesn't get pinched or kinked and you're good to go.

Since the tank breather hoses were hooked up incorrectly that also means that the flapper valve hoses are hooked up incorrectly too because the tank breather hoses were hooked up to the ports where the flapper valve hoses were supposed to be hooked up to.

So yeah Brian you're going to have to get in there and connect those vacuum hoses properly or you'll be losing power at high revs because the doorway in the airbox lid that the flapper valve is supposed to open will not be opening at all.


BTW - Thanks for the props on my bike. Got a lot more work to do on it,just no money right now to get things done.

 

:hss: Stoshmonster should be an inspector :thumbsup:
Awesome catch Bro

 

Much appreciated. :biggrin:

Today I connected the 'mystery canister'/vacuum chamber to the "T" which I think is #13 in your image above. I couldnt get a picture of the T because is tucked almost below the airbox behind the right side frame. I didnt see an easy way to get access to it, probably need to remove the airbox?

Since I already removed the evap canister the tank is now breathing properly and think Im good to go now with the flapper valve connected to the vac. canister.

Do you think there are any other lines that could have been hooked up incorrectly?

 

It's always a good idea to verify that you've done your work properly.

Take your bike out and find a nice long straight stretch of road where there's nobody else around. Make sure the engine is fully warmed up to operating temperature (because the VTEC won't work if it isn't),put the bike in second or third gear and really give it the beans.

When the VTEC switches over from two valve to four valve mode at 6800 revs the motor should pull cleanly like a raped ape all the way up until it bumps the rev limiter at redline.
If it does then you'll know for certain that the flapper valve vacuum circuit is hooked up properly now and everything is working correctly.

If the motor feels flat or is gasping for air on that run from VTEC actuation up to redline then either the flapper valve still isn't hooked up properly,there could be a hole in a vacuum line on the flapper valve circuit or a line could be pinched,kinked,or unplugged,the diaphragm in the flapper valve could have a hole in it or the doorway in the airbox lid isn't opening properly,the flapper valve vacuum solenoid electrical connector could be unplugged,or the electrical connector for the VTEC spool valve could be unplugged.

If your bike passes the test above then I'd have to say yeah you should be good to go Brian because there really isn't too much else in there that they could've screwed up.

 

Stosh

This is an old thread, but I was reading it and have a question. You mention that the flapper will not open at high revs unless the vacuum chamber/hose/etc is hooked up. I thought the flapper was normally open on a 6th gen. I have heard of people disabling the flapper, but that shouldn't hurt performance should it?

 

Nope. The flapper valve on the air box should be CLOSED at low RPM's and OPEN at high RPM's

Okay I can answer your question but I'm gonna need some help on this one. And Signal my friend since you asked the question I hereby nominate you to be my helper in performing a little Science experiment. :team2:

Alright I need you to go put on your tennis shoes and stand out in front of your house. Now I want you to walk about 100 yards down the block and walk back at a slow walking pace. I want you to breath through your nose only and pay close attention to the speed that the air passes through your nose as you're walking. Go!

Okay now I want you to walk that same 100 yards and back but this time I want you to walk at a very brisk walking pace. Remember to breath through your nose only and pay attention to the speed that the air passes through your nose as you're walking. Go!

Alright finally I want you to run that same 100 yards and back as fast as you can. Again breath through your nose only and pay attention to the speed that the air passes through your nose. Go!

Whew! Alright Signal take a little breather because this next part gets a bit tougher.

Rested up yet? Alright now my friend I want you to take your left index finger and place it along side your nose and press firmly to close off the left side of your nose so that you're now breathing only through the right side of your nose.

Hey ya goob,I said place your finger along side your nose not in it! :lol:

Okay now I want you to walk those same 100 yards and back again at a slow walking pace,a brisk walking pace,and running as fast as you can just like you did before. Keep your left index finger pressed firmly against the left side of your nose the entire time and pay very careful attention to the speed of the air as it passes through the right side of your nose. Go!

Alright now go hit the showers dude,you earned it. :cheer2::cheer2::cheer2:


Okay now let's bactrack and look at our test results for just a minute here Signal. When you were breathing normally through both sides of your nose you should have noticed that it was easy to breath. As you increased your pace the speed of the incoming air as it passed through your nose increased as well but that air was actually moving at a relatively low rate of speed until you started pouring on the coals when you were running.

When you were breathing only through the right side of your nose you should have noticed something very interesting. Because the left side of your nose was blocked off you should have noticed that the speed of the incoming air passing through the right side of your nose was much higher at any given time (whether you were standing still out in front of your house,walking slowly,walking briskly,or running as fast as you could) than it was when you were breathing normally through both sides of your nose.

That's because in order to get the same amount of air into your lungs to do the same amount of work in the same amount of time your body had to pull hard and create a strong vacuum to increase the speed of the incoming air passing through the right side of your nose.

I know what you're thinking. "Nice going Stosh! I'm tired,I'm sweaty,I've worn some rubber off the soles of my tennis shoes but WTF does any of this have to do with my question? Is this some kind of weird Mr Miyagi wax on,wax off thingy. What gives?" :noidea:

The answer my friend is,it has everything to do with your question. I would like you to read this and pay attention to the sentences that I have underlined in Red.
It's a rudimentary functional explanation of how the VTEC system works that was published in the Jan/Feb 2008 edition of Honda RedRider magazine.



As you've read in this excerpt at high RPM's your engine can efficiently fill the cylinders all on it's own because of the high piston speed,which creates an intense vacuum,which in turn massively increases the incoming air speed that then draws large amounts of fuel/air mix into the cylinder while the intake valve is open,which means you make more power when the spark plug fires and the whole thing goes BANG!

Conversely a normal engine without the VTEC system doesn't fill the cylinders as efficiently at low RPM's because the piston speed is much slower,which means that the incoming air speed is slower,which means that you draw smaller amounts of fuel/air mix into the cylinder while the intake valve is open,which means you make less power when the spark plug fires and the whole thing goes BANG!

A VTEC equipped engine on the other hand has the built in ability to fill the cylinders a little bit more efficiently at low RPM's because the pathway into the cylinders has been artificially "narrowed". By keeping one intake and one exhaust valve closed in each cylinder at low RPM's this increases the incoming air speed. (Okay technically just the one closed intake valve helps to increase the incoming air speed but since one exhaust valve is also held closed at the same time in each cylinder I guess they just threw that factoid in there for sh*ts and giggles.) This increased incoming air speed then increases the amount of fuel/air mix that gets drawn into the cylinder while the intake valve is open,which means you will make more power at low RPM's when the spark plug fires and the whole thing goes BANG!

Okay I know what you're thinking again. "Gee Stosh,thanks for that geeky engine tech lesson. :blah: That's all well and good but I didn't ask you about how the F'n VTEC system works I asked about the F'n flapper valve in the F'n airbox ya goob!" :rant:

Alright my friend now I would like you to read this. It's another excerpt from that same article in RedRider magazine.



Are you starting to see it now Signal? The flapper valve in the air box works to accomplish the exact same thing that the VTEC system in the 6th gen. engine does.

By keeping the flapper valve on the airbox closed at low RPM's you artificially "narrow" the pathway to the cylinders and your engine now has to breathe through only the right side opening in the airbox (exactly like you plugging off the left side of your nose in our little Science experiment) which as we proved absolutely increases the incoming air speed,which in turn draws larger amounts of fuel/air mix into the cylinder while the intake valve is open,which in turn will make more power at low RPM's when the spark plug fires and the whole thing goes BANG!

Honda used the flapper valve on the airbox on both the 5th and 6th gen. bikes,but unlike the 5th gen. bikes though Honda "double dipped" on the 6th gen. bikes. They installed the flapper valve to "narrow" the pathway and increase the incoming airspeed in the airbox,but then they went a step further with the VTEC system inside the engine and "narrowed" the pathway yet again (by keeping one intake and one exhaust valve closed in each cylinder at low RPM's) which increased the incoming airspeed even further.

So now at long last I can finally answer your question my friend "I have heard of people disabling the flapper, but that shouldn't hurt performance should it?"

By disabling the flapper valve and removing the little flap that covers the left side opening on the airbox you've slowed down the incoming air speed and now allowed your engine to breathe much easier at low RPM's. This means that the engine has now lost that important ability to more efficiently fill the cylinders at low RPM's that the Honda engineers originally designed into the system.

Conversely if you've disabled your flapper valve and left the little flap covering the left side opening on the airbox permanently closed you've now killed your engine's high RPM power output because your engine is literally gasping for breath trying to breathe through only the right side opening in the airbox at high RPM's.

So the answer to your question is Yes. Depending upon how you disabled the flapper valve it most certainly will hurt your engine performance. It doesn't matter if you have a 5th or 6th gen. bike either,the same holds true for both bikes because the airboxes work the same way.

I'm guessing most likely a little more power loss on the 5th gen. bikes,prolly a little less power loss on the 6th gen. bikes because of the VTEC system in the engine. Even if it's only a coupla three four ponies at most though the fact remains,you're still losing power.

Incoming air speed is EVERYTHING! You and I conclusively proved that in our little Science experiment earlier.
(Okay well mostly you Signal because you did all the actual work,I just sorta sat around in my computer chair and rambled on. I'm still taking half the credit though. :heh

Ain't Science fun........and sorta tiring all at the same time. :lol:

 

Stosh, thanks this is quite detailed and I will need to read it a few times.

I would have thought that air velocity is not the key metric hear, but rather the air volume of the air box, as the intake pulls the air. with more openings (flapper open), you may have less velocity in the air, but more volume. I would think that regardless of the amount/size of the openings, the air box would attempt to reach an equilibrium based on its size, pulling air faster through a smaller opening, or pulling air slower through a larger opening. Any ideas on that? I would think that air velocity would be a bigger deal in a forced induction type of machine vs. naturally aspirated.

 

What I meant was that the flapper on the 6th gen is "open" normally (for example the bike is shut off). Its held open by a spring. The vacuum is used to close it. So you would get more air at low RPM, and the same air at high rpm (vtec).

Mine is disabled because the last tech that dynotuned my bike said it wasn't working properly. They may just not understand what is normal for the flapper. I am going to check it out and see if its working and reconnect it if it is. I think you just have to disable the neutral switch and then you can observe it actuating as you go above 6.5k and below 6k.

 

"Key metric"? :twitch:

Gotta admit I had to Google up that term Signal. I'm taking it that "key metric" means "the most important aspect". If that's the case then no. In a normally aspirated engine air volume is not really the most important thing. As I stated previously,incoming air speed is EVERYTHING! And there's a very good reason for that.

You can have an entire ocean of air volume in your air box and it won't do you any good. All of that air is completely useless unless you can get it into the engine.

In terms of importance air volume is actually kind of secondary,however it does become very important when there's a demand for it. Don't get me wrong we do need air volume for our engine,but it's more important that we get it in there. And here's the thing,in a normally aspirated engine incoming air speed influences air volume in a very surprising way.

You prolly already know this Signal but I'm going to explain it anyway for the other forum members who are following along with the thread.

An internal combustion engine is basically just a big air pump. It draws air in on the intake side and pumps it out on the exhaust side.
In a normally aspirated engine like the one in the VFR800 as the piston moves downward on its' intake stroke it creates a vacuum that draws in fuel/air mix from the intake port in the throttle body. The faster that piston is moving downward the stronger that vacuum will be,which means more fuel/air mix will be pulled into the cylinder while the intake valve is open. The more fuel/air mix that can be pulled into the cylinder while the intake valve is open the more power that cylinder will make when the spark plug fires.

It's the amount of vacuum that the piston is pulling on its' downward movement during the intake stroke that primarily determines how fast the incoming air speed is,and thus determines the amount of fuel/air mix that gets drawn into the cylinder. Giving the engine an entire ocean of air to breathe does absolutely nothing to increase that incoming air speed.

To increase the incoming air speed we need a way to increase the amount of vacuum that the piston is pulling as it moves downward during the intake stroke.

That's not quite how the air box works Signal. There are many important aspects of an air box design but prolly the most important is the size of the opening in the air box that the engine has to breathe through. That opening has to be designed to allow enough air to pass through it to safely meet the air volume demands of the engine at it's maximum RPM. So in reality that would mean that the air box opening is optimized for high air volume flow at high RPM engine speeds.
We know that there are two openings in the air box but let's say for the moment that our VFR800 was designed with only one large opening in the air box.

Do you remember how I said earlier that air volume is kind of a secondary aspect unless there's a demand for it? Well at high RPM's the engine is spinning extremely fast which creates an intense vacuum when the piston moves downward during its' intake stroke. At this point the engine needs an absolute sh*t ton of air volume to meet its' demands.
What's important to remember here is that at high RPM's the engine is capable of producing the intense vacuum necessary to significantly increase the incoming air speed enough to pull in huge quantities of fuel/air mix all on its' own because of the high piston speeds.

Now comes the conundrum.

Our air box opening was designed and optimized to meet the air volume demands of our engine at high RPM engine speeds. (Which is great.) The thing is our engine's air volume demands are no where near as much at lower RPM engine speeds.
At that point the opening in the air box is much too large and capable of flowing way more air than what we actually need to meet our engine's air volume demands. (Which is not so great. Why put way more air into the air box than what we need if we're not going to use it.)

So when you think about it Signal having one large opening in our air box is kind of an engineering compromise isn't it? It flows enough air to safely meet the demands of our engine at high RPM's (Which is what we want because our engine needs that huge amount of air volume at high speeds.) but it flows way more air than what our engine actually needs at low RPM's. (Which is what we don't want because it slows the incoming air speed.)

I gotta think at this point the Honda engineers looked at each other and said 'We can do better than this and make our engine a little more powerful and more efficient at lower RPM's". And that's where the "variable air intake control valve" (More commonly known as the "flapper valve".) comes into play.

Okay so let's be very clear on this point my friend,the flapper valve comes into play only during low RPM engine operation.

According to the Honda factory service manual that I have it clearly states that the flapper valve is OPEN at idle speed. The reason it's kept open at idle speed is because we aren't really concerned with making large amounts of power at idle speed. We just want the engine to breathe nice and easy and continue to stay running. That's all we want,nothing more.

The manual then states that under acceleration "with increasing engine speed quickly" (Those were the exact words that were used.) the flapper valve will then CLOSE and it will remain closed until the throttle is rotated beyond 38 degrees of throttle rotation or the engine speed is increased beyond 6500 RPM's.

If you exceed either one of those criteria the flapper valve will then OPEN and it will remain open until under deceleration you either rotate the throttle back to a point less than 35 degrees of throttle rotation or reduce the engine speed to less than 6000 RPM's. The flapper valve will then CLOSE once again.
Obviously when you return the throttle to station keeping and the RPM's drop to idle speed the flapper valve will then OPEN .

Okay so we've got all this opening and closing going on with the flapper valve at low RPM's but what exactly were the Honda engineers trying to accomplish here? Alright let's start with what we know.

1. In a normally aspirated engine like the one in the VFR800 incoming air speed is EVERYTHING.

2. It's the vacuum produced by the piston moving downward on the intake stroke that primarily determines how fast the incoming air speed is.

3. The faster the incoming air speed is the more fuel/air mix that will be drawn into the cylinder while the intake valve is open. The more fuel/air mix that gets drawn into the cylinder the more power that cylinder will make when the spark plug fires.

4. At high RPM's the engine is capable of producing the intense vacuum necessary to significantly increase the incoming air speed enough to pull in huge quantities of fuel/air mix all on its' own because of the high piston speeds.

5. An air box with one large opening that was designed and optimized to meet the air volume demands of an engine at high RPM's works great at high RPM's but flows way more air volume than the engine actually needs at low RPM's.

6. Having an entire ocean of air in the air box at low RPM's is completely useless unless you can get it into the cylinder while the intake valve is open.

7. At low RPM's the pistons are moving at a much lower rate of speed than they are at high RPM's. Because the pistons are moving more slowly they create less vacuum on the intake stroke. Because they create less vacuum they pull in less fuel/air mix while the intake valve is open which means that the cylinder will produce less power when the spark plug fires.

Now that we've got our known points of reference let's do another quick Science experiment.

Let's say I'm standing at the end of a hallway,there's a door at the end of this hallway and I've got my hand on the door knob. The hallway is just tall enough and wide enough for an average sized guy to move down the hallway where his feet are on the floor,his head is just touching the ceiling,and his shoulders are touching the walls on either side of him.
There's going to be a group of guys walking down this hallway. I'm going to open the door and hold it open for a very specific amount of time and then close it.
Alright let's say I opened the door and 5 guys were able to walk through it before I closed it.

Now then,same hallway,same me,same guys,only this time those guys are going to be running at twice the speed that the first group of guys were walking. I'm going to open the door and hold it open for exactly the same amount of time as I did before but now 10 guys are able to run through the door before I closed it.

The test conditions were exactly the same in both tests,the only thing I changed was the rate of speed that the guys were moving at. How does that relate to the flapper valve you ask? Well do you remember I said earlier in my post that to increase the incoming air speed we needed a way to increase the amount of vacuum that the piston is pulling as it moves downward during the intake stroke. We know that at high RPM's the engine is perfectly capable of doing this all on its' own but how do we do that at low RPM's?

The answer is the flapper valve. Instead of using just one large opening in the air box the Honda engineers used two smaller ones. They then installed the flapper valve which changes the way that the engine breathes at low RPM's and forces it to breathe in a way that it normally would not do.
The engine now has to breathe all of the air that it needs to safely meet its' air volume demands at low RPM's through a much smaller opening in the air box.
That's exactly like you plugging off the left side of your nose in our first Science experiment which we conclusively proved absolutely does increase the incoming air speed.

Don't worry about the engine having to breathe through that restriction at low RPM's though,an internal combustion engine is capable of much higher efficiency than your body is so it can perform this task with ease.
Need proof? Think about this then,there are only two small openings in the air box that the engine breathes through at high RPM's.
Yep that's right,even at high RPM's the engine is breathing through a restriction in the air box. Why? Because we've got a normally aspirated engine and we want to keep the incoming air speed as high as we possibly can.

Okay so whatta we got here,by breathing through a much smaller opening in the air box that was designed and optimized to meet the air volume demands of the engine at low RPM engine speeds means we now.....

1. Increase the amount of vacuum that the piston is pulling as it moves downward on the intake stroke because the engine now has to breathe through that small restriction. (Which is what we want. :thumb

2. Because of the increased vacuum that the engine is now pulling this increases the incoming air speed. (You know we really want that in our normally aspirated engine. :thumbsup

3. Because of the increased incoming air speed the engine now has a much greater demand for air volume at low RPM's. (Yep we definitely want that too. :whoo

4. Because of that increased incoming air speed and greater air volume demand the engine is now drawing in much more fuel/air mix into the cylinder while the intake valve is open. (Holy smokes this just gets better and better don't it. :shocked

5. Because of all that extra fuel/air mix that gets drawn into the cylinder while the intake valve is open the engine now works more efficiently and produces more power at low RPM's. (Aw yeah baby just slather that low RPM power all over me with a trowel! :hump

The one duct/two duct air box design on the VFR800 is kind of a bizarre concept to wrap your head around Signal because it works sorta bassakward from what you would think.
You would think that by disabling the flapper valve you would be doing your engine a favor by letting more air get into the air box and allowing it to breathe easier at low RPM's,but that's just not the case.

Disabling the flapper valve and leaving the doorway on the left side of the air box open does in fact open two pathways for the air to get in but all that serves to do is slow down the incoming air speed at low RPM's. Remember we've got a normally aspirated engine here,WTF would you wanna do that for? All you've got now is 5 guys worth of fuel/air mix walking into the cylinder.

If you left the flapper valve alone and let it do it's job properly you increase the incoming air speed,which in turn increases the amount of incoming air volume,and now you've got 10 guys worth of fuel/air mix running into the cylinder producing more power for you at low RPM's. Which one would you rather have?

By opening the doorway on the left side of the air box at low RPM's and allowing the engine to breathe through both openings in the airbox you actually get less air volume into the engine at low RPM's.

By keeping the doorway on the left side of the air box closed at low RPM's and forcing the engine to breathe through only the small opening inside the snorkel on the right side of the air box you actually get more air volume into the engine at low RPM's. Bizarre isn't it!

Do you see what I mean now about incoming air speed influencing air volume in a very surprising way?

Okay I can hear your question already, "Why the heck did the Honda engineers go to all that trouble just to give me a little more low RPM power?"
Think about this for just a minute Signal,in your normal day to day riding how often and for how long do you actually use the high RPM power on your bike?

You might use it to accelerate up to speed on a freeway on ramp,you might use it to make a pass on some slow moving traffic,you might use it to race your buddies every now and again. I mean unless you're a chronic speeder or a freakin' crazy lunatic squid that's really about it. So the honest answer is you're actually using the high RPM power very little of the time.

The Honda engineers went through all that trouble to give you a little more low RPM power because that's the area of the rev range that you use all of the time. Makes good sense doesn't it.

This has been a long post I know but I've got one more thing for you to ponder my friend. I've read that it's a pretty popular mod to remove the snorkel from the air box on the 5th and 6th gen. bikes. It makes the intake honk a lot louder,and yeah I gotta agree it sure does.
But here's the thing,take a good look at the size of the hole in the right side of the air box with the snorkel removed. Now take a good look at the size of the hole inside the snorkel.

If you've left the flapper valve alone and simply removed the snorkel from the air box (yep you guessed it) you're still losing power at low RPM's because the right side of the air box was designed to breathe through the small opening inside the snorkel and not through the big honkin' hole that you now have in the right side of the air box.

Ain't this Science stuff fun..........and kinda long winded and boring all at the same time. :lol:

 

your a regular bill Nye The Science Guy

 

Stosh, That was a great series of posts to help explain (to us simpletons...) how the flapper system works and why you need it. Seriously - it was the best. Your explanation was humorous and very understandable!

In fact after reading it I ran to my bike - well maybe walked - and reconnected my flapper. I had been getting an off-idle stumble and hesitation that i thought was just inherent to the design. Yesterday it was there and i was just accepting it. Now today it's gone! Thanks!

Good Job!