As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED ENGINE WOULD RANDOMLY LOSE >500 RPM AND THAT ENGINE WAS ROUGH RUNNING. MECHANICS WERE ABLE TO DUPLICATE THIS ISSUE ON THE GROUND AND DISCOVERED THAT THE RIGHT MAGNETO CAPACITOR WAS LOOSE IN MAGNETO'S HOUSING. THE MAGNETO HAD BEEN INSTALLED THE PREVIOUS DAY AND HAD ACCRUED 3 HOURS IN SERVICE SINCE 500 HOUR INSPECTION PERFORMED BY OTHER REPAIR STATION.