On July 4, 2002, about 1330, eastern daylight time, an unregistered Kenneth Parmerter Loehle 5151 Mustang amateurbuilt airplane, operated by a private individual, as a Title 14 CFR Part 91 personal flight, crashed while attempting to land at the Lake Persimmon Airstrip, Lake Placid, Florida. Visual meteorological conditions prevailed, and no flight plan was filed. The private-rated pilot received minor injuries, and the aircraft incurred substantial damage. The flight originated in Lake Placid, Florida, the same day, about 1327. The pilot stated that he was conducting a test flight in the traffic pattern at Lake Persimmon Airstrip for the owner/builder, whom he was assisting to build and test the accident airplane, and he had just made a low pass over the runway in order for the owner who was on the ground, to listen to the engine being operated at full power. He said he maneuvered the airplane on the downwind, and was turning to base when he noticed a reduction in engine rpms so he "steepened" the turn in an attempt to make it back to the runway, and stalled the airplane. He said the airplane fell like a rock, and he knew he had stalled it, because the controls had little or no affect. The airplane impacted the ground with the right wing down, at a near 45-degree angle with the horizontal, shattering the wooden right wing and damaging the fuselage. An FAA licensed airframe and powerplant mechanic with an inspection authorization rating, examined the accident airplane and stated that the engine had been improperly installed and had not been properly vented back to the expansion tank. He said he found hot spots on the cylinder head, consistent with there having been trapped air in the cylinder head and excessive internal temperatures in the engine that caused the engine to cease operating.