1991 Johnson/Evinrude EI 60 thru 70 outboards Service Manual, Page 28Get this manual
Weather, Altitude and Engine Performance The horsepower ratings of all engines are those that would be obtained under standard conditionsHowever, changes in weather and altitude will affect the performance of any outboardSome factors that will decrease the output of an engine are: Low barometric pressure High temperature High humidity High altitude
Performance can decrease noticeably when an engine is run on hot, humid daySometimes the weather or altitude alone can cause the engine RPM to drop below the recommended operating rangeIn such case, lower pitch propeller can be used to bring RPM back into the operating rangeIn any case, top boat speed will not be as high as on cool, dry dayINotel loss of engine performance can occur if an engine has not been properly modified for high altitude operationIf you service high altitude engines, consider ordering Information and Decal Kit, PIN 393533, from your distributorTo avoid permanent powerhead damage, be sure that an engine modified for high altitude operation is properly identified and returned to original calibration if operated at or near sea level