1995 Johnson/Evinrude Outboards 50 thru 70 3-cylinder Service Manual, Page 34Get this manual
Tune-Up Procedure 1Visually inspect engine for leaks, missing or loose parts, or the obvious defects2Compression checkProper compression is essential for good engine performanceAn eng ine with uneven compression cannot be properly tuned Operate the engine until it reaches norma operating temperature Stop engine Remove and inspect all spark plugsCheck their condition Install thread-type compression tester in spark plug hole With throttle in wide-open positioncrank engine with starter through at least four compression strokes Variation between cylinders should not exceed 15 PSI (100 kPa)IF the engine has equal compression, is hard to start, AND operates poorly, check for: scored cylinder walls damaged pistons stuck piston rings worn piston rings
IF the engine shows variation greater than 15 PSI (100 kPa), check fordamaged head gasket damaged pistons broken or stuck piston rings scored cylinder walls