On my 1997, whenever it's been running for a while and shut off, if I open the fuel cap I hear a hiss. I think it's air going into the tank rather than escaping the tank. I've checked the tank vent and can blow into and suck air out of it by mouth. Any ideas on why it seems like it's not venting?

 

Normal
Both the tank vent and fuel cap are designed to vent pressure and vacuum
at +/- 3psi in order to keep the fuel in the tank in a roll over