1973 Evinrude Norseman 40 HP Service Manual, Page 31Get this manual
DISASSEMBLY OF MAGNETO All components may be removed from the armature plate by removing the attaching screwsThe spark plug high tension leads can be pulled from the coil and lamination assemblies
CLEANING, INSPECTION, AND REPAIR
SPARK PLUGS Inspect plugs for cracked porcelain and worn electrodesClean the electrodes with point fileDO NOT sandblast spark plugs Adjust gap to the specified .030 inchIn re-gapping, adjust only the ground electrode, as attempting to bend the center electrode will crack the insulatorSee Figure 4-7Poor motor performance and premature spark plug failure may result from improper spark plug installationBefore installing the plug, be sure the plug seat in the cylinder head is clean and free from obstructionsSee Figure 4-8Install new spark plug ga sket, screw the plug in by hand, then tighten to the spec,i fied 17-1 to 20-1 foot pounds ,
Figure 4-7Checking Spark Plug Gap
Figure 4-8 Cleaning Spark Plug Seat