THE OPERATOR BORROWED THE HELICOPTER FROM THE OWNER UNDER A VERBAL STIPULATION THAT AUTOMOTIVE FUEL WOULD NOT BE USED. THE ACCIDENT HELICOPTER WAS NOT APPROVED FOR AUTOMOTIVE GASOLINE UNDER THE PROVISIONS OF AN STC. HOWEVER, THE OPERATOR WAS KNOWN TO REFUEL HIS HELICOPTERS WITH AUTO GAS. THE PURPOSE OF THE FLIGHT WAS TO ERADICATE FROST FROM CITRUS TREES. AFTER REFUELING, THE HELICOPTER LOST POWER AND DESCENDED STRIKING WIRES AND TREES. THE OPERATOR DRAINED THE FUEL FROM THE HELICOPTER ON THE GROUND AND TRANSPORTED IT TO HIS FACILITY. THE ACCIDENT WAS REPORTED FOUR DAYS LATER. EXAMINATION OF THE FUEL SYSTEM REVEALED A SMALL QUANTITY OF FUEL WITH EVIDENCE OF AUTO GAS. LABORATORY ANALYSIS OF FUEL SAMPLE REVEALED SAMPLE HAD THE SAME AROMATIC QUALITIES AS AUTO GAS. ACCORDING TO THE FAA, THE ONSET OF CARBURETOR ICE WILL OCCUR QUICKER WITH AUTO GAS THAN WITH AVIATION FUEL. WEATHER CONDITIONS WERE CONDUCIVE TO FROST FORMING ON FRUIT TREES.