1990 Johnson Evinrude "ES" Colt/Junior thru 8 Service Manual, P/N 507870, Page 36Get 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 areLow barometric pressure High temperature High humidity High altitude
hot, humid daySometimes the weather or altitude alone can cause the engine RPM to drop below the recommended operating range In any case, top boat speed will not be as high as on cool, dry day
f41 Performance can decrease noticeably when an engine is run on a