It is also very important to make sure the engine has no air locks, if the system has no leaks then it should be easy to bleed out any air that would normally be trapped in the top hose, or highest points of the inlet manifold (SUs. and Strombergs have a bleed pipe in the 'V' at the top, these normally need clearing).
The Edelbrock and Offenhauser manifolds often trap air behind the thermostat, this can be overcome by drilling a small hole in the top area of the thermostat but is not normally required.