1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Manual, Page 49Get 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 out boardSome factors that will decrease the output of an engine areLow barometric pressure High temperature High humidity High altitude
t!J when it is run on hot, humid daySometimes the weather
or altitude alone can cause the engine RPM to drop below the recommended operating range In 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 dayA loss of engine performance can occur if an engine has not been properly modified for high altitude operation If you service high altitude engines, consider ordering Information and Decal Kit, PI 393533, from your distributor