INADEQUATE PREFLIGHT BY THE PILOT, AND HIS FAILURE TO ASSURE THAT PROPER MAINTENANCE/ANNUAL INSPECTION WAS ATTAINED. FACTORS RELATED TO THE ACCIDENT WERE: WATER AND OTHER CONTAMINATION IN THE FUEL SUPPLY, LACK OF CONTINUITY IN TWO IGNITION LEADS, LOOSE LEFT MAGNETO ON THE RIGHT ENGINE, AND IMPROPER TIMING OF THE RIGHT MAGNETO ON THE RIGHT ENGINE; TERRAIN CONDITIONS IN THE EMERGENCY LANDING AREA AND THE PILOT'S FAILURE TO USE A SHOULDER HARNESS PROBABLY ATTRIBUTED TO THE DEGREE OF INJURY AND DAMAGE.