What was found
RH MAGNETO ON RH ENGINE RAN ROUGH DURING PREFLIGHT RUNUP. ENGINE CLEARED UP AFTER LEANING MIXTURE FOR 2 MINUTES. TAXIED TO RUNWAY. DURING TAKEOFF RUN THE ENGINE WAS UNABLE TO PRODUCE SAME TAKEOFF POWER AS LH ENGINE, SO PIC ABORTED TAKEOFF. HE DID ANOTHER RUNUP ONCE EXITING THE ACTIVE RUNWAY. HE WAS NOT ABLE TO CLEAR UP THE ENGINE ISSUE THIS TIME. HE CALLED COMPANY MAINTENANCE AND DESCRIBED ISSUE. DOM/MECHANIC VERIFIED MAGNETO WAS RUNNING ROUGH BY PERFORMING ANOTHER RUNUP. REMOVED MAGNETO LEAD HARNESS AND FOUND LIGHT CORROSION AND MOISTURE ON THE DISTRIBUTOR BLOCK AND SPRINGS ON LEAD HARNESS. MECHANIC CLEANED LEAD HARNESS AND INSTALLED OVERHAULED MAGNETO OF SAME MODEL AS REMOVED AND TIMED TO ENGINE. PERFORMED ANOTHER RUNUP AND MAGNETO DROP WITHIN LIMITS, THUS OPS CHECK OK. FOUND THAT ISSUE WAS DUE TO MOISTURE CAUSING CORROSION ON DISTRIBUTOR BLOCK AND WAS NOT AN ACTUAL FAILURE OF THE MAGNETO ITSELF. THIS AIRCRAFT OPERATES IN ALL WEATHER CONDITIONS FREQUENTLY (INCLUDING RAIN AND SNOW). IT ALSO IS NOT HANGARED MOST NIGHTS WHEN AWAY FROM HOME BASE (AT LEAST 5 TIMES PER WEEK). WE HAVE DECIDED TO INCREASE OUR INSPECTION INTERVALS MORE FREQUENT THAN THE CHAMPION/SLICK SERVICE BULLETIN (SB1-86C) STATES OF EVERY 500 HOURS IN SERVICE.