As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING RUN-UP BEFORE TAKEOFF, THERE WAS EXCESSIVE RPM DROP ON RT ENGINE, RT MAGNETO. REMOVED RT MAGNETO. REMOVED BACK COVER AND MAG HAD A BURNED ELECTRICAL ODOR. REMOVED COIL AND FOUND TO BE ARCING TO CASE. LOOKS LIKE THERE WAS A SMALL CRACK IN COIL HOUSING. INSTALLED NEW MAGNETO AND RETURNED ACFT TO SERVICE.