On September 25, 1999, at about 1130 eastern daylight time, a Banting Glasair II, N55BP, registered to a private owner, operated by the pilot as a 14 CFR Part 91 personal flight, experienced a total loss of engine power in the vicinity of River Ranch, Florida, and a forced landing was made to a marshy area. Visual meteorological conditions prevailed and no flight plan was filed. The airplane sustained substantial damage. The private pilot reported no injuries. The flight originated from Lakeland, Florida, about 45 minutes before the accident. The pilot stated he had been working on a fuel problem with the airplane for the last 2 1/2 months. He had replaced several components on the engine, and the problem went away. He decided to take the airplane on a cross-country flight in preparation for a longer flight. Upon arrival at the destination airport, he called UNICOM and another airplane reported in for landing. He eventually entered the traffic pattern for a left downwind to runway 16. Power was reduced to 2,000 rpm, the airspeed decreased to 140, and flaps were lowered. The engine started to sputter. He increased power, turned the boost pump on, and changed the fuel selector valve from the main tank to the header tank with negative results. He informed UNICOM that he would be unable to make the runway, and turned the airplane to line up with highway 60 as a forced landing area. The approach was discontinued due to vehicle traffic. He made another turn towards a marshy area located next to the highway, and made a forced landing. Examination of the crash site by the FAA revealed the forced landing area was unsuitable, and no other forced landing areas were available. No determination could be made as to the cause of engine roughness or stoppage resulting in the accident.