was on an IFR flight from Coral Harbor to Repulse Bay when the pilot encountered a rough running engine. An in-flight magneto check resulted in the engine quitting completely when the right mag was selected. The pilot made a forced landing and was able to relay his situation to an overflying Northwest Airlines a/c who passed the information on to the Rankin Inlet FSS. The FSS relayed the report to Edmonton ACC and RCC. Edmonton ACC informed Winnipeg ACC about the a/c and that there were no injuries and no damage to the a/c. A helicopter was dispatched to assist the pilot who declined to be airlifted out, and who said he was attempting to fix the a/c and fly it out. The pilot had survival gear and was in no immediate danger. The pilot changed a burnt spark plug and was able to get airborne and fly to Repulse Bay. The pilot later took the a/c to Arviat, NWT where it is based and will be fitted with a new ignition harness.