As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED ROUGH RUNNING ENGINE. AFTER INSPECTION OF BOTH MAGNETOS, IT WAS FOUND THAT THE INTERNAL PARTS WERE BURNED AND DETERIORATED. THIS CONDITION WAS FOUND AT 225 HRS AFTER THE 500 HR INSP. BOTH MAGNETOS DID OT REACH THE 500 HR INTERVAL.