1998 Johnson Evinrude "EC" 90, 115 SPL Service Manual, P/N 520209, Page 32Get 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 engine with uneven compression cannot be properly tuned Operate the engine until it reaches normal operating temperatureStop engine Remove and inspect all spark plugsCheck their condition Install thread-type compression tester in spark plug hole With throttle in wide-open position, crank engine with starter through at least four compression strokes Variation among cylinders should not exceed 15 PSI (100 kPal
INote On "v" engines, the average pressure readings might vary
between the port and starboard cylinder banksThe averages of the port and starboard pressure readings should not vary by more than 15 PSI (100 kPalIF 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 kPal check for: damaged head gasket damaged pistons broken or stuck piston rings scored cylinder walls IF the engine has equal compression and runs normally, continue the tune-up procedure