INFLT ENCOUNTER WITH ICING. PLT LATER QUESTIONS TIMELINESS OF DECISION IN HIS CHOICE OF ALTERNATE ARPT DURING THE DIVERSION AND FLT ASSIST.

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I WAS WBOUND ON V-6 AT 4000 FT WHEN I UNEXPECTEDLY ENCOUNTERED FREEZING RAIN. TRIED TO CLB TO WARMER AIR BUT ACCUMULATED 1 1/2 INCHES OF ICE BY 7000 FT; SO REVERSED COURSE TOWARD PSB AND DSNDED TO 4000 FT. USING FULL PWR TO MAINT 120 MPH; ATC VECTORED FOR ILS TO PSB. COULD NOT MAKE AN APCH DUE TO COM PROBLEM FIRST AND THEN NAV EQUIP MALFUNCTION (POSSIBLY DUE TO ICED-UP ANTENNA). AFTER DELAYS OF ABOUT 30 MINS; I WAS VECTORED TO CAPITAL CITY ARPT (CKY) FOR A VFR DSCNT AND LNDG. I WONDERED LATER WHY I HAD NOT PROCEEDED DIRECTLY TO HARRISBURG; WHICH I KNEW WAS VFR. DEPARTING CXY THE FOLLOWING MORNING; I WAS AWARE OF AN EXHAUST ODOR WHEN I TURNED THE HEAT ON DURING CLBOUT. I TURNED THE HEAT AND DEFROSTER OFF AND OPENED AIR VENTS FOR REMAINDER OF FLT. HAD THE MUFFLERS REMOVED FOR INSPECTION AND FOUND A HOLE ABOUT 1 INCH DIAMETER IN FRONT MUFFLER NEAR AIR INLET. GLASS BEAD BLASTING REVEALED 3 OTHER AREAS OF LEAKAGE IN THE SAME VICINITY THAT WERE NOT OBVIOUS TO THE NAKED EYE. I BELIEVE CARBON MONOXIDE AFFECTED MY JUDGEMENT AT PHILIPSBURG AND RECOMMEND USE OF A CARBON MONOXIDE DETECTOR DURING COLD WX.