if i used a fuel pressure regulator with an electric fuel pump, could i set the pump @ 40psi and then the regulator at like 12 so that i could use it with a carb?

 

A fuel pump has an output flow that varies with discharge pressure. You can't "set the pump @ 40psi". The system pressure, assuming the pump is large enough, is set one of two way:

1) by the fuel pressure regulator, which controls pressure by either bypassing flow back to the tank and using a dead-end rail system, or,

2) uses a looped rail system and controls the pressure by control the return line from the rail.

For a carb, you typically have a "dead-end" application - no fuel rails. So you need a fuel system that is connected with a "bypass" type fuel pressure requlator. Then, assuming your pump was capable of operating at low pressures, and that your regulator is capable of recycling the right volume of fuel, you could set the system pressure via the regulator to supply 7psi.

It sounds like you may be trying to patch a carb into a recirculated EFI system, and it isn't going to work if the fuel system was connected to flow everything through the rail(s).

I would start with a "low pressure" fuel pump, then use a bypass type system pressure regulator, rather than trying to patch into a high pressure EFI system.