Fuel vent cap closed or open when running the boat?

[Rkuruvilla]

Just realized that there is a fuel vent hose which is closed on the outside with a plastic threaded cap. I understand that when adding fuel the vent cap needs to be open to to allow smooth gas flow into the tank. My question is when running the boat on water does this fuel vent cap need to be open? (Mercury 90 2stroke on a SeaArk bass boat). Thanks in advance. I also appreciate all the advice I was given in this forum on other boat/outboard matters.

 

[Chris1956]

Are you talking about the vent on the cap of a portable fuel tank? Those need to be left open when the engine is running and closed when in storage.

 

[Rkuruvilla]

build-in fuel tank.

 

[Bondo]

build-in fuel tank.

Ayuh,..... I've never seen a capped vent on a built in tank,.....