On Sunday morning, September 5, 1993, at 0930 mountain daylight time, a Westholm Vans RV-6, N16JL, owned by the pilot, impacted terrain during an emergency forced landing at the Flying B Ranch Airstrip, Salmon, Idaho. There was no flight plan filed for the personal flight, conducted under 14 CFR 91 in visual meteorological conditions, that had just taken off for McCall, Idaho. The private certificated pilot and the one passenger aboard were not injured. The aircraft was substantially damaged. There was no fire. The pilot reported the aircraft lost engine power about 50 feet above the ground during initial climb after takeoff. He said he initiated an emergency forced landing to the only open area available and the aircraft left wing struck a fence post during landing roll. An examination of the aircraft after the accident revealed the gascolator drain valve was locked in the open position. The pilot indicated he was unaware the drain valve could lock in the open position. The loss of engine power was duplicated on another RV-6 aircraft with the drain valve open (See work order 1374).