The certificated commercial pilot and a passenger were returning from a short cross country flight and the pilot decided to do a touch and go landing. As the airplane was climbing out, the passenger noticed a small flame on the side panel, about 6 inches forward of the left door post. The pilot executed a 180 degree turn back to the runway. The flames in the cockpit rapidly spread around the base of the windshield and up into the overhead ceiling. Due to the heat and smoke, the passenger and pilot jumped from the airplane as it was still moving down the runway at about 30 mph. The unoccupied airplane exited the runway and rolled to a stop between the runway and taxiway. The airplane was consumed by fire. The pilot and passenger were seriously injured. The origin of the fire appeared to be from a fuel line located in the left front doorpost area. Electrical wiring to the landing and position lights was also routed through the door post.