Fuel tank breather

Does every tank need one? Ive got a 3.5 v8 series3 which has a fuel cell in the rear. It has two outlets on the top, fuel out and a return. It also has a take off halfway down the side that went to the swirl pot. Ive since changed the fuel injection back to carbs, so ive done away with the swirl pot and lifter pump and gone back to a facet pump. This all means that i havent got a breather pipe/valve in the top of the tank. Am i right in thinking i need one for air to replace the used fuel. Please help fella's, i want this thing finished!!

Check to see if there's a breather hole in the fuel cap - it's how the series ones work. Fuel pipe out, filler pipe in, fuel filler bypass pipe to let the air out while you fill it and a hole in the filler cap covered with a gauze filter (probably to prevent explosion risk on petrols).