As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) THE SEAL FOR THE BUTTERFLY VALVE IN THE CARBURETOR AIR BOX (FOR CARBURETOR HEAT) SEPARATED AND WAS SUCKED UP INTO THE CARBURETOR. THIS CAUSED THE ENGINE TO LOSE PERFORMANCE WHICH MADE THE PILOT RETURN FOR A LANDING. TOWER REPORTED SMOKE (LIKELY FROM A RICH MIXTURE) TAILING THE AIRCRAFT. UNEVENTFUL LANDING. AIRCRAFT REMOVED FROM SERVICE. NOW REPAIRED AND BACK ON LINE.