As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ENGINE EXPERIENCED LARGE MAG DROP, ON LEFT MAGNETO, DURING RUN-UP. MAGNETO WAS REMOVED AND INSPECTION FOUND THE IMPULSE COUPLING SPRING WEAK AND NOT RETURNING TO ITS NORMAL RUN POSITION. THE IMPULSE COUPLING WAS DISASSEMBLED AND A BROKEN SPRING WAS FOUND.