Weeping Gas Tank Vent

[Wanderer]

Hello,
I've posted on another thread on this topic before. Since my bike is STILL having the issue I've been looking harder at the root cause. I believe there is some sort of evaporation/condensation cycle going on. So now I'm looking for others thoughts on my thoughts. From what I can see the over pressure vent actually vents up through the gas cap then back down through the vent hose. There is an orange rubber looking bellows towards the rear of the filler that will mate with the hole in the cap once it is closed. I believe the vent hose to gas cap mating is the issue. Whenever my bike weeps if I open the tank the orange rubber bellows is wet. If it is sealing correctly against the cap it should be dry near the center hole of the bellows. So a couple of possible issues, 1) the spring (if there is one) is not strong enough to seal to the cap when the tank heats up or 2) the sealing surface between the cap and the orange bellows leaks because of a poor sealing surface on the cap. My cap does not look very good as far as a smooth sealing surface goes plus it looks like there is a groove in the cap that the bellows definitely does not line up. Any other thoughts out there? :'(
Later,
Norm

 

[stevepsd]

Hello,
I've posted on another thread on this topic before. Since my bike is STILL having the issue I've been looking harder at the root cause. I believe there is some sort of evaporation/condensation cycle going on. So now I'm looking for others thoughts on my thoughts. From what I can see the over pressure vent actually vents up through the gas cap then back down through the vent hose. There is an orange rubber looking bellows towards the rear of the filler that will mate with the hole in the cap once it is closed. I believe the vent hose to gas cap mating is the issue. Whenever my bike weeps if I open the tank the orange rubber bellows is wet. If it is sealing correctly against the cap it should be dry near the center hole of the bellows. So a couple of possible issues, 1) the spring (if there is one) is not strong enough to seal to the cap when the tank heats up or 2) the sealing surface between the cap and the orange bellows leaks because of a poor sealing surface on the cap. My cap does not look very good as far as a smooth sealing surface goes plus it looks like there is a groove in the cap that the bellows definitely does not line up. Any other thoughts out there? :'(
Later,
Norm

The orange bellows connects the OUTPUT of the gas cap venting system to the vent line. So gas vapor goes up thru the very bottom of the gas cap (remember the gas cap is sealed by the sealing ring a 1/2" up from the bottom of the cap). The gas vapor then makes it way thru the venting passages in the cap and makes it way to the output of the gas cap vent system. This vent hole in the cap is connected to the gas cap vent line (thru one of 2 copper lines inside the tank - the other is the filling area drain - which come out underneath the tank) via the Orange bellows. The gas then runs down thru the copper vent line, out the bottom of the tank to one of the two rubber lines which terminate in front of the motor.

If the Orange bellows does not seal correctly, the gas will pool in the tank filler opening and drain out using the filler opening drain.

The bellows is wet because liquid gas in in the venting system. A number of 49 state bike users (including me) have notices our bikes literally pissing gas out the vent line when the tank is near full and the outside temps are up. I don't think any Calif bikes are exhibiting this problem due to the charcoal canister in the the vent system, although I suspect there will be other side effects of this for CA bikes, as the charcoal canisters do not respond well if filled with liquid fuel (they are designed for vapor).

Don't have a solution to this yet. Never had a modern bike that exhibits this problem.

 

[Wanderer]

Hi Steve,
Yep, you're right. It would have to get pass the rubber gasket on the bottom of the cap. One other thought, my line will weep regardless of how much gas is in the tank, just needs a little sun to get it started. And one more thought, when the tank is heated up this is the first bike that I can remember that did NOT give that sigh of pressure relief when you opened the cap.
Later,
Norm

 

[hojo in sc]

Are you seeing this all the time, or just when you park on the side stand?

 

[stevepsd]

Mine does it on either the side stand or centerstand. So far, it needs to be at least 80F-ish with no more than a gallon or so used to cause it to vent overboard.

Now, mine will be a bit worse this year than everyone elses in this regard since I removed the filler neck restriction this past December (which forces you to have a dead air space in the top of the tank). Even though it has been 95F+ so far the past couple of days I have not had a near full tank to determine how much my modified tank will vent overboard...but it sure did last summer.

 

[Wanderer]

Howdy,
Which stand it is on does not matter though worst on the side than the center.
Later,
Norm