You retorque every season to 35 ft./lbs. on a cold engine and you do it in the order indicated in the Seacraft Yellow Book of Atomic 4 Maintenance Obscurities.
As for the vent, the odds are excellent that it's occluded. You find it by looking at the tank top: the 3/8" to 1/2" hose leading up from the tank that ISN'T the fuel
fill (usually 1 1/2" wire-wound fire-resistant hose) and by following it to the deck edge or coaming where there is usually a little chromed vent cap. If you undo the vent line
from both ends and blow it out, you'll likely evict three types of spiders and their little webby graves.