Vent Hose

[El Prosecutor]

Are you supposed to run a vent hose from the blower down to the bottom of the bilge, since gas vapors are heavier than air?

[502 JET]

Yes you are correct.On my fishing boat with an enclosed engine compartment I have a large louvered intake with two hoses on it one short and the other long reaching to the bottom of the bildge.The fan is in the outlet pipe and the hose extends down to the bildge with the other half of the exhaust louvers open to pull air out when running.The exhaust louvers should face aft and the intake face forward.

[Boatcop]

502 speaks the truth.
Make sure the blower is positioned to blow OUT of the engine compartment, and not into it.
Blower is kind of a misnomer. It should be called a "SUCKER", since it's designed to suck the gas vapors out of the engine or fuel compartment.
The exhaust hose should be in the lowest possible spot in the bilge, without getting submerged by any water that may be present.
The intake hose should be at about carb leve, if possible. The theory is that the action of carb intake draws air into the compartment, so that even at idle and/or slow speeds, there's effective ventilation.