What was found
PILOT REPORTED AIRCRAFT SEEMED TO BE SHORT ON POWER DURING CLIMB. AIRSPEED WAS SLIGHTLY BELOW EXPECTED. PILOT PERFORMED AN IN FLIGHT MAG CHECK AND NOTED THAT ENGINE WAS VERY ROUGH ON LH MAGNETO. AFTER RETURNING TO MAINTENANCE A GROUND RUN WAS PERFORMED. NORMAL MAG CHECK RPM OF 2000 DID NOT EXHIBIT NAY PROBLEMS. WHEN CHECKING AT FULL POWER ( 2500RPM AND 42 " HG), THE ENGINE STUMBLED SIGNIFICANTLY WHEN ON THE LH MAG. AN INSPECTION OF THE MAGNETOS AND HARNESSES WAS SATISFACTORY. SPARK PLUGS WERE REMOVED, INSPECTED AND TESTED WITH STANDARD SPARK PLUG MACHINE, NO DISCREPANCY NOTED. EACH SPARK PLUG WAS THEN TESTED USING AN OHMMETER AND SEVERAL WERE FOUND TO HAVE AN EXCESSIVE AMOUNT OF RESISTANCE WITH A COUPLE HAVING NO RESISTANCE. THERE IS NO PUBLISHED VALUES FOR THIS PARAMETER, BUT THERE ARE VARIOUS SUPPLIERS AND GROUPS WHO HAVE CONFIRMED THE RESISTANCE VALUE HAS AN EFFECT ON THE PLUG OPERATION. IT SHOULD BE NOTED THAT THE CHAMPION SPARK PLUG MACHINE CT475-AV WILL NOT TEST THE PLUGS PROPERLY UNLESS THERE IS SUFFICIENT AIR PRESSURE SUPPLIED ( ABOVE 140 PSI). SPARK PLUGS SHOULD BE CHECKED CLOSELY UPON REACHING 700 HOURS.