According to the pilot, the aircraft had just come out of a maintenance period where placards were installed on the fuel selector panel. The fuel selector has a handle and a pointer, which, according to the pilot, are similar in shape and size. The pilot said that he had never moved the fuel selector valve from the main tank position since he purchased the aircraft. The valve was apparently found in the 'header tank' position after the accident. The header tank only holds 4 gallons of fuel and is for emergency use only. The pilot thought the fuel selector was positioned to the main tank. The aircraft had been airborne for 15 minutes when the engine suddenly quit. The pilot lined up for a landing on a road, however, when the aircraft was on short final a school bus turned onto the road directly in front of the aircraft. The pilot turned left to avoid colliding with the bus and hit a large tree.