What was found
AFTER A NORMAL RUNUP, PRIOR TO TAKEOFF THE ACFT ENGINE FAILED TO PROVIDE FULL POWER AND STARTED TO MISS ON TAKEOFF ROLL. THE TAKEOFF WAS ABORTED AND THE ACFT RETURNED TO THE RAMP. A TIMING CHECK WAS DONE AND MAGNETO, PN 4370, SN 14061319, WAS FOUND TO HAVE TIMING THAT VARIED BY OVER 10 DEGREES. WHEN CHECKING THE FIRING FROM 1 CYLINDER TO ANOTHER THE MAGNETO WOULD FIRE AT DIFFERENT TIMES, VARYING BY AS MUCH AS 10 DEGREES. THE MAGNETO WAS REMOVED AND A NEW MAGNETO WAS INSTALLED. A RUNUP WAS DONE AND THE ACFT RAN NORMALLY. WHEN THE MAGNETO WAS RETURNED TO THE SHOP, NOTICED THAT THE SN WAS COVERED BY SB1-15. ACCESSED THE DISTRIBUTOR CAP AND FOUND THAT THE ELECTRODE FINGER OF THE DISTRIBUTOR CAP WAS NOT LOOSE AND COULD NOT HAVE CAUSED THE FAILURE.