gas tank vent question

[fireguyfire]

I have a 1994 Campion cortes 16.5 open bow with a 115 merc outboard on it, and I really like the whole setup. My boat has a factory fuel tank under the rear floor, with a filler neck that comes out to the left of the motor (viewed from the rear) and a tank vent line which comes out the rear of the boat to the right of the motor (as seen from the rear). The vent is a factory chrome vent with a screen in it.
My question is, when the boat is over 2/3 full of fuel, and it is nice out, I tend to get a gas leak backing out of the vent which is both an environmental problem, and an eyesore. Is this normal? Should fuel be able to come out of the vent, or is only air supposed to get out/in? Is something broken in my fuel system?

 

[kjsAZ]

Unfortunately that happens quite often...
Check your vent line and make sure it's straight going up with no loops. If you have loops or bends in there what happens is that some gas gets shot up into that area and when the fuel warms up or evaporates a bit this gas gets pushed out the vent.
The same issue is when the vent hose goes downwards or below tank level from the tank.

There are some devices which are supposed to prevent that but according to BoatUS they mostly don't work well:
http://www.boatus.org/findings/40/

 

[Chris1956]

See if you can run the vent line all the way up, as high as possible in the hull, and then down to the vent fitting. That will minimize the splash leaking you are seeing.

 

[fireguyfire]

An update; found that the clamp that held my vent line straight up of the tank up high had rusted and broken. I fixed it so my vent hose now does straight up off the tank about 18", then does a 90 and goes straight across level to my vent. My vent hose was sitting lower than the top of the tank after the clamp broke, and then made a couple of loops going up. I'm sure I've solved my vent issue, but Ian curious if having a fuel filled vent line would have been affecting the running/ performance of my motor at all? If so, what should I notice that's different?

 

[Bondo]

An update; found that the clamp that held my vent line straight up of the tank up high had rusted and broken. I fixed it so my vent hose now does straight up off the tank about 18", then does a 90 and goes straight across level to my vent. My vent hose was sitting lower than the top of the tank after the clamp broke, and then made a couple of loops going up. I'm sure I've solved my vent issue, but Ian curious if having a fuel filled vent line would have been affecting the running/ performance of my motor at all? If so, what should I notice that's different?

Ayuh,.... The Highest point in Yer hose has to be Higher than the vent outlet, so's splashed water drains Out, not into the tank,.....