Outboard Gas Tank Question

[Saxacussionist]

I have been wondering about something for a while and really can't find any information on it.

I have a Honda 8 HP outboard on my 26S which is always connected to the gas tank. When finished sailing for the day, I always close the vent on the tank to keep the fumes contained and prevent condensation from the heating and cooling it goes through every day. The question is - what is all that increased pressure doing to the carb? Can I assume that, with the motor tilted up, that increased pressure doesn't shove more gas into the carb? Is the needle / float valve really that good at keeping all that pressure in check?

What do you recommend: Vent open, vent closed, or vent closed but hose disconnected?

Thanks!!

[Don T]

Hello,
I do not own a honda so I'm postulating here.
Yes, pressure build up in the tank will force fuel up into the carb.
No, the needle and seat cannot hold the pressure since the motor is tilted up and the float won't. Excess fuel will run out of the carb air inlet into the air box and either run down the motor and into the motor well / water or it will evaporate before it gets there. The more expansion room in the tank the less pressure build-up there is.

Advice for long term storage:
Disconnect the hose at the tank, make sure the ball bearing / o-ring seals the hose from dripping. Same for the tank fitting
Close tank vent.

This way no fuel is leaking into the environment provided the fuel hose and all fittings are in good shape.
No fuel is leaking into the bilge (same proviso).
The tank can expand and contract as needed without forcing fuel out or letting air / moisture in.
The hose is still attached to the motor protecting the fittings from the elements. Not the hose though which will degrade from the UV exposure. If you disconnect both ends of the hose you just have to clean the motor fitting before re-attaching the hose. No biggie really and saves the hose from UV rot.

[Catigale]

Gas (petrol) into the environment isn't really that damaging, as its vapor pressure is so high it evaporates PDQ and leaves the marine life alone. I crack my vents during the heat of the day, close at night.