OK You have a fuel line going into the pump and a line coming out going to each cylinder and at the end of the line is the injector screwed into the head. From your description it sounds like you are talking about the lines exiting the pump. Leaking there means you are not getting full fuel volume to the injector. I don't see how air can affect the engine at that point. The fuel should have a higher pressure than the air hose. To find the leak clean the pump with soap and water and dry it off. Turn over the engine, to pump fuel, just enough to find the wet spot. Some have used talcum powder to help seeing the leak.