The pilot was delivering a recently purchased airplane for a friend and decided to land for fuel. While in the landing pattern the engine lost all power. The pilot immediately turned toward the runway, switched the fuel selector valve from both to the left tank position, then to the right tank, and back to both while he attempted to restart the engine, without success. The pilot conducted a forced landing to a field. During the landing the airplane struck and came to rest in Mesquite trees about 100 yards north of the airport. The airplane sustained substantial damage to the right wing outer leading edge, the left leading edge of the horizontal stabilizer, the firewall, and the fuselage lower skin. After the accident, the pilot checked the fuel level. When he removed the first fuel cap, he noticed the sound of air rushing into the fuel tank. Further examination by the FAA revealed dry, hard dirt consistent with a Mud Dauber nest blocking the fuel tank vent tube. They also found the right fuel cap vent was deteriorated and inoperative and the left fuel cap was not a vented cap. The FAA stated about 6 gallons total fuel remained in both right and left fuel tanks. The airplane did not have a current annual inspection.