Dutchman's pipe vine AKA Aristolochia is a whole genus of hundreds of plants that grow from zone 4 (NE US) into the tropics. Without information about which kind you have, this question is difficult to answer. Where are you? Can you take clear close-ups of the flowers and leaves and a photo of the plant overall and post on the Name that Plant forum to get IDed? Do pollenators visit the flowers? Have you tried hand pollenating with a paintbrush, moving pollen from one flower to another?