Just because your regulator is new, does not necessarily mean it is good, take off the 17 mm plug with a Phillips head, and check your lp pressure should be 5 psi, or 35 kpa if it is a newer Nissan that can be monitored through the meter panel. After verifying correct pressure, turn off the key and monitor pressure drop on your gauges to verify no leakage internal to the injector holder or its associated relief valve, also if you smell fuel coming from the air filter this is an indication of too much fuel pressure causing the relief valve to vent the excess pressure. If all that checks well check your basics, sometimes the slots in the distributor need to be cleaned off.