HISTORY OF FLIGHT On July 25, 2011, about 1205 eastern daylight time, an experimental amateur-built RV-6, N164BF, was substantially damaged when it collided with a guardrail during a forced landing to a roadway following a total loss of engine power while in cruise flight near Hartford, Kentucky. The certificated commercial pilot/owner/builder and his passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the flight that departed Bowling Green Warren County Regional Airport (BWG) Bowling Green, Kentucky. The personal flight was conducted under the provisions of 14 CFR Part 91, with an ultimate destination of Whitman Regional Airport (OSH), Oshkosh, Wisconsin. The pilot reported to the Federal Aviation Administration (FAA) that the airplane was in cruise flight at 7,000 feet mean sea level (msl) when he moved the fuel selector from the left main tank, which contained 100LL aviation fuel, to the right-hand auxiliary tank, which contained automotive gasoline. The engine ran for a short time before it "stumbled," lost power, and the pilot began troubleshooting the power loss. He turned on the electric fuel boost pump, but the fuel pressure gauge showed no pressure. The pilot switched back to the left main tank, but could not restart the engine. Fearing a broken or disconnected fuel line due to the zero fuel pressure reading, the pilot elected to shut off the fuel and perform a forced landing to a road. During the landing, the airplane struck a guardrail, which resulted in substantial damage to the engine firewall structure. PERSONNEL INFORMATION According to FAA records, the pilot held a commercial pilot certificate with a rating for airplane single engine land and instrument airplane. He also held a flight instructor certificate with a rating for airplane single engine land and instrument airplane. His most recent third-class FAA medical certificate was issued on July 14, 2010. The pilot reported 2,643 total hours of flight experience, of which 360 hours were in the accident airplane make and model. AIRCRAFT INFORMATION According to FAA records, the airplane was manufactured by the pilot/owner in 2005, and was equipped with a 150-horsepower Lycoming O-320-E2D engine. The airplane's most recent conditional inspection was completed on March 15, 2011, at a total airframe time of 234 hours. METEOROLOGICAL INFORMATION The 1153 recorded weather observation at Owensboro-Davies County Airport, Owensboro, Kentucky, located approximately 20 miles northwest of the accident location, included scattered clouds at 2,400 feet, wind from 260 degrees at 8 knots, 10 miles of visibility, temperature 32 degrees C, dew point 26 degrees C, and an altimeter setting of 30.05 inches of mercury. WRECKAGE AND IMPACT INFORMATION Examination of the airplane at the scene by an FAA inspector revealed several fuel system components and screens partially or fully occluded with particles that resembled rust, and material with the appearance, odor, and consistency of varnish. According to the pilot, he had not utilized the auxiliary fuel tanks in "eight or nine" months, and serviced them with fuel just prior to departure on the accident flight. During recovery of the airplane, the lowest point in the fuel system drain was removed. This was located just underneath the fuel selector valve in the cockpit. The drain cock was corroded, and the pilot stated that when he removed the drain cock in order to drain the fuel, the left auxiliary tank drained, but the fuel from the right auxiliary tank did not. The pilot stated that had to “poke a straw” in the hole in order to get fuel to flow. The pilot explained in the NTSB Form 6120.1 Pilot/Operator Aircraft Accident/Incident Report Form that, due to intermittent use, fuel had dried in the auxiliary fuel line and formed a "varnish type sludge that was pulled through the selector valve blocking the primary fuel filter when I selected the auxiliary tanks at 7,000 feet. [The] filter blocked all fuel supply to the engine."