LOSS OF PWR IN IMC CONDITIONS DEV FROM ALT.

Narrative

MADISON TO EAU CLAIRE. I FILED FOR AND WAS CLRED FOR 4000 FT ENRTE. THE FLT WAS CONDUCTED IN IFR CONDITIONS FROM THE DELLS N. AFTER ENTERING CLOUDS I ADDED CARB HEAT AND PITOT HEAT AND PROCEEDED NORMALLY. THE OUTSIDE TEMP WAS 0 FAHRENHEIT. THERE WAS NO INDICATION OF ICE ON WINGS OR WINDSCREEN. APPROX AT TOMAH THE ENG COUGHED AND ALMOST DIED. I NOTIFIED CHICAGO CENTER OF THE PROBLEM AND INDICATED THAT I DID NOT WISH TO DECLARE AN EMER. I SWITCHED TANKS; MAGS; AND CHANGED CARB HEAT TO NO AVAIL. REDUCING THE THROTTLE BROUGHT THE ENG BACK TO RUNNING SMOOTHLY AT 15 INCHES. THAT PWR SETTING WAS INSUFFICIENT TO MAINTAIN ALT WITHOUT STALLING. ALT DRIPPED TO 3000 FT BEFORE I WAS ABLE TO ADD SUFFICIENT PWR TO INITIATE A SLOW CLB BACK TO 4000 FT. I CONSIDERED LNDG AT BLACK RIVER FALLS BUT CHANGED MY MIND. THE ENG BEGAN TO RUN NORMALLY AND THE APCH AT BLACK RIVER WOULD BE AN ADF TO NEAR MINS. I LOST RADIO CONTACT WITH CHICAGO CENTER AND WAS UNABLE TO ESTABLISH CONTACT WITH MINNEAPOLIS CENTER. EVENTUALLY CONTACT WITH MINNEAPOLIS CENTER WAS REESTABLISHED. I RECEIVED A CLRNC FOR AN ILS APCH TO 22 AT EAU CLAIRE. PERHAPS IN THE ANXIETY OF THE SITUATION; I FAILED TO VERIFY THE OM AND PROCEEDED WELL PAST THE APCH COURSE. WHEN I REALIZED THE MISTAKE I DECLARED A MISSED APCH AND PROCEEDED TO THE VOR INBOUND. CONDITIONS AT EAU CLAIRE HAD IMPROVED SO THAT AT 3000 FT. I HAD GND CONTACT THROUGHOUT THE APCH. WHILE PROCEEDING TOWARD THE VOR I REALIZED I WAS OVER THE FIELD. I ADVISED CENTER THAT I WOULD CANCEL IFR AND LAND SINCE I WAS IN VFR CONDITIONS AND HAD THE FIELD IN SIGHT. 2 MECHS HAVE LOOKED AT THE ENG. THERE ARE 2 THEORIES: 1. WHEN I CHOSE CARB HEAT FOR AN EXTENDED OP WITHOUT LEANING THE MIXTURE; THAT MAY HAVE FOULED THE PLUGS. THE FOULED PLUGS WOULD OPERATE AT REDUCED PWR GIVING THE OPPORTUNITY TO GO ON TO EAU CLAIRE. 2. THE ACFT I FLY IS AN SMA THAT HAS NO ALTERNATE AIR. THE AIR CLEANER ELEMENT IS FOAM RUBBER AND ON LNDG IN EAU CLAIRE WAS FOUND TO BE SATURATED WITH WATER. IT IS POSSIBLE THAT THE MOISTURE FROZE DURING THE FLT AND THAT THE REDUCED AIR AVAILABLE TO THE ENG CONTRIBUTED TO A RICH OP THAT COULD HAVE FOULED THE PLUGS. THE PLUGS ARE IN REASONABLE SHAPE AND HAVE OPERATED NORMALLY SINCE THIS INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO. MAINT IS CONVINCED THE PROBLEM WAS CAUSED BY FOULED PLUGS AS A RESULT OF NOT LEANING AND THE CONTINUOUS USE OF CARB HEAT. THEY DO NOT FEEL THE AIR CLEANER ELEMENT HAD ANYTHING TO DO WITH THE LOSS OF PWR. THE PLUGS HAVE BEEN CHANGED AND THE ACFT OPERATES FINE. IT IS OWNED BY A CLUB AND NO OTHER MEMBERS HAVE HAD ANY PROBLEMS.