I was told running return lines to the gas tank instead of the fuelinjection pump resavour would fix the vaporlock problem on 502 efi mags. I did this but the fuelinjection pump empties the resavour faster than the mechanical pump can fill it so it runs out of gas . Any more ideas ?

Are you sure the mechanical pump is keeping up? Could it possibly be going bad?

why don't you just dump the mech pump and get a proper electric efi pump and regulator and never look back ?