No fuel pressure at normal engine temp

[lafarm]

Have mechanical fuel pump and electric pump on toggle switch have dual 97 type carbs a fuel block with pressure gauge all braided stainless lines fuel pressure is good when cold with just the mechanical or with electric on but after driving a few miles gauge shows 0 pressure and will run out of fuel with just the mechanical but will keep running with the electric turned on even tho the gauge still shows 0 pressure also has a fuel pressure regulator have tried setting it from 2 to 5 lbs pressure which works when cold nothing when warmed up. Thinking maybe a bad line but need some ideas. This is on my 52 Victoria.