You have to make sure you get enough volume and pressure, but not enough pressure to overcome the inlet needle in the carb. Often the spun aluminum tanks will starve the engine of fuel when they are getting low. One way to keep the pressure the same with full or low fuel is to use the pump and put a tee in the pressure line that goes to the top of the tank. Fuel pressure will then always be the same as without the pump, but a full tank of fuel.