THE PRIVATE PILOT APPLIED POWER FOR A GO-AROUND ABOUT 300 YARDS PAST THE APPROACH END OF THE RUNWAY. WITNESSES INDICATED THAT THE ENGINE DID NOT SOUND AS IF IT WS PRODUCING FULL POWER. THE AIRPLANE STRUCK A TREE TOP AND CRASHED. THE INVESTIGATION REVEALED THAT THE FUEL SYSTEM WAS CONTAMINATED BY SAND AND RUST. THE CARBURETOR HEAT CONTROL WAS IN THE 'ON' POSITION. THE AIRPLANE HAD AN ANNUAL INSPECTION 14 HOURS PRIOR TO THE ACCIDENT. THE AMOUNT OF POWER AVAILABLE COULD NOT BE QUANTIFIED OR VERIFIED.