If the fuel system has has been overhauled, the vent could be inside the fuel cap. Most of the newer ones are there. If you are having a vent problem with suction, just leave the fuel cap off or loose and if the problem goes away, it's most likely the vent. If problem persists, it's not likely the vent unless it's a problem with filling the tank. If the tank is burping when you try to fill it, then it could still be the vent.