As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB PILOT NOTICED LEFT ENGINE SOUNDED ROUGH AND DECIDED TO RETUN TO THE AIRPORT AS PRECAUTION. UPON EXAMINATION MAINTENANCE PERFORMED LEFT ENGINE COLD CHECK AND REPLACED CYLINDERS #1, #3, AND #5 TOP SPARK PLUGS AS PER LYCOMING OH MANUAL CHAPTER 4. PERFORMED GROUND RUNUP AND NO ISSUES FOUND, ENGINE OPERATING AS NORMAL.