On October 8, 1994, about 1030 hours mountain daylight time, N21LJ, a Larsen Avid Heavy Hauler home built airplane, operated by the owner/pilot, was substantially damaged during a forced landing in Nampa, Idaho. The forced landing was precipitated by a loss of engine power during climb. The private pilot and his passenger received minor injuries. Visual meteorological conditions prevailed and a flight plan was not filed. The personal flight departed from Nampa and was conducted under 14 CFR 91. The pilot stated that the engine failed about 250 feet above the ground while on climbout after takeoff from the Nampa Municipal Airport. The pilot attempted to re-start the engine, but to no avail. The pilot stated that he then was forced to land in a rough field located about one mile from the airport. The airplane impacted the rough field and was substantially damaged. The wreckage was examined at the accident site by an FAA Aviation Safety Inspector from Boise, Idaho. According to the inspector, fuel was found in both wings and both engine carburetor float bowls. No evidence of fuel contamination was found. Oil was found in the oil injectors. The ignition system was functionally tested via the starter and spark plugs with no abnormalities noted. The Rotax engine was rotated by hand; it was free to turn with no internal stoppage noted. No pre-impact mechanical malfunctions were found during the examination of the airframe and engine.