Auto Parts: fuel pressure, fuel pressure regulator, carbuerator

Question
what should the fuel pressure be on a 1991 ford 5.0 with a carbuerator when it is at an idle?

Answer
    They didn't make carburetted 302s in 1991.  If you are trying to convert the EFI engine to a carburetor, then you can't use the fuel pump that is in the tank.  It produces around 40 psi.  The most you might need for a carburetor is 4 or 5 psi.  You could try to use a fuel pressure regulator that is designed for carburetted engines, but it won't work very well.  Cutting the pressure down that much is going to be hard on the regulator; it wasn't designed to do that.  Plus, you won't be bypassing fuel like the EFI regulator does.  The fuel pump is cooled by the constant flow of fuel going through it, as well as by being submerged in the tank.  But it takes both to keep it cool.  So, you have two choices.  You can install an external electric pump that was designed for carburetted engines.  There are lots of them out there and they don't cost more than about $50.  It will have to be mounted low--even with the bottom of the tank.  These pumps are designed to push fuel, not pull it.  You could even rig a toggle to the in-tank pump so that you could use it to prime the other pump if it ever drained down(just like they do in airplanes).  But you should use a spring-loaded toggle because you absolutely can't leave that pump on while the engine is running.  The aftermarket pump should be able to draw the fuel through the old pump, there isn't much resistance.  Make sure the tank vent is clear, or it will vacuum-lock.  The other choice is to install a regular mechanical fuel pump.  If you are using the original engine, the pump boss will be covered by a block-off plate.  That has to come off so that the pump can be installed.  The timing cover will have to come off, as well, because you will have to install a fuel pump eccentric on the timing gear.  The EFI engines didn't have one.  If you are using another engine that came with a carburetor, then just hook it up to the fuel pump on that engine, and disconnect the electric pump in the tank.  You won't have to worry about the pressure then, the mechanical pump will deliver a satisfactory pressure on its own.
    Just remember: you CANNOT use the electric in-tank pump with the carburetor.