1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Manual, Page 161Get this manual
Pyrometer Procedure 1Install correct test propeller and place engine in test tank ill
J:Twist and remove spark plug leads before changing
propellers to avoid accidental starting of engine
2Start engine and run at 3000 RPM for at least five minutes'3l 3Reduce engine speed to 900 RPMAt 900 RPM, digital pyrometer should indicate 1400 15 (60 C) when held
on cylinder head If engine temperature is not within this range, troubleshoot cooling system to determine problem