As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) WHILE DOING CIRCUITS, THE ENGINE BEGAN TO RUN ROUGH WITH PARTIAL POWER LOSS. THE AIRCRAFT LANDED AND POST-FLIGHT INSPECTION FOUND NR 3 CYLINDER HAD 2 DEAD SPARK PLUGS AND NR 4 CYLINDER HAD A SPARK PLUG WITH BROKEN CERAMIC. ALL THE ENGINE SPARK PLUGS WERE REPLACED AND THE ENGINE WAS GROUND RUN SERVICEABLE.