1987 Pulsar Nx Se 1.6 dohc Seems to be excessive pressure in fuel tank which causes a leak by the filler hose where it meets the gas tank. Tried changing the clamps, cleaning the hose and found when we release the gas cap and the pressure is released it stops. Are the gas caps vented or not?

It might just be a bad gas cap.

You could try asking around in the Nissan forums to see if anyone else has had a similar experience.