Fuel tank venting 1963 Mercury Monterey
 

Need some information. My 1963 mercury Monterey has a none vented fuel cap. On the sending unit it has two outlets. One goes to the fuel pump and the other is clamped off. Should the clamped off connection be open to vent or is there another location for the vent? This was this way when I bought the car. It does run sluggish and I am now wondering if the engine is not getting enough fuel due to vacuum in tank? Any help is appreciated.