As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MAGNETO PRESENTED LARGE INTERMITTENT RPM DROP DURING PREFLIGHT RUNUP CHECK. FLIGHT WAS TERMINATED AND AIRCRAFT RETURNED TO HANGAR FOR MAINTENANCE. UPON DISASSEMBLY OF MAGNETO IT WAS DISCOVERED THAT THE CONTACT POINT CONNECTED TO THE STEEL "SPRING" HAD COME LOOSE. THIS SET OF CONTACT POINTS HAVE BEEN IN SERVICE FOR 13.5 HOURS.