fuel pressure for nitrous...

heres the thing,want to start small,have 47n 36f jets.going to run 5 psi of fuel to fuel solinoid.have a press reg and it goes to gas sol.put a gauge on it and itwill bottom the gauge out over 15 psi.i only have one fuel pump 18 psi electric.sumped tank 1/2 inch fuel line to dash 8 to split then to both reg.the carb i have set at 7 pounds .the other wont regulate down.reg is good works ifyou switch them.whycant i get the press down to the fuel sol?