As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED VIBRATION AND ENGINE SPUTTER AND LOSS OF RPM DURING CLIMB FROM TAKEOFF. MAINTENANCE PERSONEL INSPECTED IGNITION SYSTEM, FUEL SYSTEM. NO DEFECTS NOTED. PERFORMED DIFFERENTIAL PRESSURE CYLINDER LEAK CHECK AND NOTED CYLINDER #4 WAS ABNORMALLY LOW AND LEAKING BY EXHAUST VALVE. BORESCOPE INSPECTION CONFIRMED BURNT EXHAUST VALVE.