If the motor was started with the throttle even slightly open, the engine computer, EMM, senses that something is not right and will not allow the motor to accelerate. If the throttle linkage, throttle shafts, or postition sensor on the motor are a bit sticky or corroded, one or more of the items could keep from returning to fully closed.
The same thing happens if the shift switch on the motor is loose, out of adjustment, sticking, or faulty. In that case the EMM thinks that the motor is still in neutral and will not allow it to rev up.
If it does not operate correctly when you are sure the throttle is completely closed on starting, see your Evinrude dealer for assistance.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.