As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT NOTED INTERMITTENT ROUGH ENGINE AND FLUCTUATING EGT. DURING SUBSEQUENT TROUBLE SHOOTING, NOTED ONLY ONE IMPULSE COUPLING SOUND. WHEN PULLING ENGINE THROUGH WITH SPARK PLUGS OUT AND TIMING WAS WAY OFF. UPON REMOVAL FOUND THAT COULD BARELY TURN THE MAGNETO BY HAND. WHEN MAGNETO WAS OPENED, THERE WAS RUST SHOWING ON ROTOR AND COIL WEDGE WAS LOOSE.