THE HELICOPTER HAD DEPARTED THE RANCH FOR A LOCAL AREA PLEASURE FLIGHT WHEN AT APPROXIMATELY 300 FEET AGL A LOSS OF POWER OCCURRED. IT WAS OVER A HEAVILY WOODED AREA. THE PILOT ATTEMPTED TO EXTEND THE GLIDE BY PULLING IN COLLECTIVE PITCH AND MAKING A RIGHT TURN (QUARTERING TAILWIND) TO THE ONLY AVAILABLE CLEAR AREA. THE MAIN ROTOR RPM CONTINUED TO DECAY AND THE HELICOPTER DESCENDED VERTICALLY OUT OF CONTROL TO IMPACT ONTO THE OPEN FIELD. THE SKIDS COLLAPSED AND THE HELICOPTER ROLLED RIGHT. POST-ACCIDENT EXAMINATION OF THE WRECKAGE REVEALED THAT A MISALIGNED P-LEAD WIRE IN THE MAGNETO HAD CHAFED AND ARCED. ADDITIONALLY, BOTH P-LEAD CAPS WERE FOUND LOOSE. THE DIRECTOR OF MAINTENANCE FOR THE OPERATOR STATED THAT HE AND HIS MECHANIC DID NOT ADJUST THE MAGNETO TIMING BECAUSE IT WAS TO HARD TOO REACH ON THE HELICOPTER. THE ENGINE WAS TEST RUN WITHOUT DUPLICATION OF THE POWER LOSS.