On May 12, 2005, about 0955 eastern daylight time, an American General AG-5B, N1193G, registered to and operated by a private individual, experienced a loss of engine throttle control resulting in a forced landing short of the approach end of runway 31, at St. Augustine Airport, St. Augustine, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 91 personal flight from Haller Airpark, Green Cove Springs, Florida, to St. Augustine, Florida. The airplane was substantially damaged and the private-rated pilot, the sole occupant, was not injured. The flight originated about 0930, from Haller Airpark. The pilot stated that the preflight, takeoff, and flight en route to the St. Augustine Airport were normal. He contacted the tower when the flight was about 10 miles west and was advised to fly left base for runway 31. The tower cleared him to land when the controller had a visual with the aircraft, and he turned base at about 1,200 feet. He slowed the airplane and lowered flaps, and while on final approach he applied power to adjust the sink rate but the throttle "... was just loose in my hand (like it completely disconnected from the carburetor)." Unable to increase power, he advised the tower of the situation, and after recognizing that he was unable to land on the runway, ditched the aircraft in a marsh short of the runway. The airplane flipped inverted during touchdown and he exited and signaled to rescue personnel that he was okay. According to the FAA airworthiness inspector who examined the airplane, the carburetor linkage separated from the carburetor at the ball assembly. Examination of the ball assembly revealed no signs of excessive wear. No determination was made as to the reason for the separation.