As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) WHILE PERFORMING PRE-FLIGHT ENGINE RUN UP, WHEN RIGHT MAGNETO WAS SELECTED, THE ENGINE BEGAN TO RUN VERY ROUGH ALMOST TO THE POINT OF STOPPING. THE AIRCRAFT RETURNED TO THE HANGAR AND THE FLIGHT WAS CANCELLED. DECIDED TO REMOVE BOTH MAGNETOS AND INSTALL A SPARE SET WHILE THESE WERE SENT TO A COMPONENT REPAIR FACILITY. (TC# 20190325012)