My old girl has a habit of acting like she has a mixture problem that is intermittent. She starts fine but after a few miles wants to die and wont run with any throttle or load. Wait a few minutes and she moves again. Problem is inconsistent. Don't know if it is a fuel pickup problem, air leak or other carb problem. Don't see or hear any air leak. Fuel pump has been replaced today and still acting unruly. Previous owner commented that it ran out at about 1/4 from empty. I ran it dry, or so I thought, the other night but now with 5 gallons of fuel in the belly it still has the same sporadic symptoms. Any thoughts on a process of elemination?