1997 Johnson Evinrude "EU" 90, 105RW, 115, 150, 150W, 175 60 LV Service Manual, P/N 507268, Page 34Get this manual
Tune-Up Procedure 1Visually inspect engine for leaks, missing or loose parts, or other defects2Compression checkProper cylinder compression is essential for good engine performanceAn engine with damaged pistons, piston rings, or cylinder walls cannot be properly tuned Operate the engine until it reaches normal operating temperatureStop engine Remove and inspect all spark plugsCheck their condition Install hread-type compression tester in spark plug hole Be sure engine battery is in good condition and fully chargedWith throttle in wide-open position, crank engine with starter through at least four compression strokes The lowest cylinder reading should be at least 80 ofthe highest cylinder reading
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 kPa)IF the engine has acceptable compression, is hard to start, AND operates poorly, check for: scored cylinder walls damaged pistons stuck piston rings worn piston rings