Where does this go?

I have a 5th generation. I'm working on my bike for the first time, so sorry if this sounds like a stupid question.

Took on the simple task of changing the air filter. No problems. Except....

When I was done and lowered the gas tank back down, I see there are 2 hoses that are not connected to anything. Apparently when I pivoted the tank back to access the air filter, I must have caused these hoses to detach.

Both of these hoses are black with a faint red stripe on them. Both are connected to "front" of the tank, right next to one another.

One of them is thicker than the other - maybe 1/2 outside diameter and 1/4 inside diameter (roughly). I easily spot where this attaches to, follow the hose, and it appears to be an overflow that would empty on the left side of the bike, about where the oil drain plug is. No worries there.

The other hose is thinner in diameter. There's only about 12 to 15 inches of play in it form where its attached to the tank and where the hose ends. At the end of the hose, there's a plastic elbow.

For the life of me, I can't see where this second, thinner hose is supposed to connect.

I started the bike, ran it, and no problems. No leaking. No strange sounds.

Any input would be appreciated.

Thanks in advance.

 

http://vfrworld.com/forums/mechanics-garage/1189-problem-after-installing-k-n-filter.html

Maybe this link will help , Pliskin, especilly the last post.

 

The thick one goes to the small hole underneath the fuel cap, it's a drain in case you overfill the fuel tank.

The thin one is a vent for the fuel tank. They just kinda end up underneath the bike, If the thin one is obstructed your tank won't flow fuel for long...like holding your finger over the end of a fluid filled straw. Make sure this hose doesn't get kinked when you drop the front of your tank down. Numerous times I've seen bikes run out fuel for this reason. I've also seen a fuel tank collapse almost like a crushed aluminum can when a customer got the bright idea of plugging it.

You can tell for sure if you open up the fuel cap and blow in the end underneath the bike...the air should come out inside the tank. If you can't blow through it you best find out why.

 

The gold doohickie? Is that next to the tin colored slush pump? Freakin' hoses can be so confusing.

The Honda shop manual has several pages of real nice illustrations on hose and cable routing. I've always appreciated that.

 

Thanks guys, I appreciate it.

 

That's the flapper valve vacuum diaphragm. Closes the air box flapper valve at low rpm's.

 

So after reading this thread, I decided to take another look under my tank...I remembered something odd when I re-charged he K&N Filter. It looks like the PO removed the hose from the flapper valve and plugged the hose...basically dis-abling the flapper valve. I thought I read some people say they did it to keep the flapper open all the time...any reason for this or any harm in having it this way?


EDIT:
Well, I just did some searches on the flapper valve, and it seems that disabling it may give you a bit more top end speed but reduce low RPM torque. I am wondering if that is what the PO was looking for. I doubt I will ever hit the top speed of this bike (or very rarely) so I think I will plug that hose back in.

2nd EDIT after more searching:
I think it does reduce low RPM power. Some 6th gen folks like it because they said it smoothed out acceleration.

Any comments/opinions?

 

I thought, correct me if I'm wrong, that the flapper valve is closed at low rpms to keep the vacuum at a certain level so you don't lose power and then it opens up at higher rpms when more airflow is needed. Seems it's used to optimize the air flow without losing any power. At least that was my understanding of it. Correct me if I'm wrong, please.

 

You might be right. All I know is I got sick of the 'flap-flap flap-flap' noise at low speed and disconnected the hose which leaves it in the open position. No problems, just a little more airflow.

I always read it was there to reduce induction noise at low speed and only opened as more airflow was needed.

 

It's sounding like one of those "6 of one, half dozen of another" type of mods. I'll have to try it both ways and see if the noise bothers me, acceleration is better or not as smooth, etc.

Any harm in having it disabled? I can;t imagine there would be, but I am not that mechanically gifted to know.

 

disabling will just cause you to lose some torque down low is all I think anyways.


as far as getting more top end...lol...how? it's suppose to be open then...so maybe if you removed it completely perhaps...but like you'd notice that anyways. I say leave it as stock. The flapping noise isn't bothersome.

 

ROGUE RACING CBR1000RR Intake Flapper Valve page

Another opinion, this makes sense when you consider the flapper is clutch activated. It pops open going in to first gear at a crawling pace, not much need for additional air at that point.

 

I've tried both options on the flapper valve and decided to leave it disconnected. I didn't see much difference either way. No noticeable difference on low end performance. Maybe a very slight increase in sound but I like not having it flapping open and closed.

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