As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EXPERIENCED ENGINE ROUGHNESS ON LEFT ENGINE, 5-10 MINUTES AFTER DEPARTURE, AT CRUISE ALTITUDE OF APPROXIMATELY 2,500 FEET MSL. ISOLATED THE PROBLEM TO THE RIGHT SIDE OF LEFT ENGINE DUAL MAGNETO AND CONTINUED THE FLIGHT ON THE LEFT SIDE OF DUAL MAGNETO(RIGHT SIDE COCKPIT SWITCH OF DUAL MAGNETO TURNED OFF ON LEFT ENGINE UNTIL REACHING THE AIRPORT.