1974 Johnson 40 HP Outboard Motors Service manual, Page 71Get this manual
PROPELLER SELECTION GENERAL
Selection of the correct propeller Is one of the most critical factors in achieving satiSfactory performance of boat and motor Propellers must be custom selected to match the motor to the boat, load or application(SELECTION OF AN INCORRECT PROPELLER CAN CAUSE SERIOUS DAMAGE TO THE MOTOR
NOTE The 40 engine should be propped so that it nms in the 45004700 RPM range at lull throttle with average loadProlonged operation in the 4100 200 RPM range hould be avoidedThis is very important, espeCially if used in commercial operation whe re this RPM range is maintained for extended periods of time
When shipped from the factory, the motor is equipped with propeller that will give satisfactory performance under average conditionsHowever, since some
boats have speed potentials that are quite high or low, it may be necessary to install propeller having
NOI PISTON ON TOP DEAD _