Engine will not run past 4800 rpm’s / 45 mph. Starts easily and runs smoothly otherwise. Just will not reach the proper WOT rpm’s & speed. Have had this problem for the last couple months. Boat has been checked out and serviced by two different shops and after extensive testing (compression, injector operation, throttle opening, sensor voltage, controls and linkage, fuel pressure, fuel pressure, vacuum gauges, cylinder drop test etc etc.) they were not able to identify a single issue.
Any Help would be greatly appreciated!
The basic diagnostic procedures have to be performed correctly by a tech who understands what the engine data means. With the diagnostic software, factory training, the service manual, and both pressure and vacuum gauges a tech should be able to diagnose a lack of power issue with a water test of the rig. this assumes that the boat is not underpowered, the correct prop is installed, the motor is rigged correctly for the type of boat, and the controls and electrical system are functioning properly. What is the pertinent boat information and what propeller is installed? When did it last run well and was anything done to the boat or motor between those times?
An engine only needs the correct amount of fuel, adequately compressed, then ignited at the correct time and expelled through the exhaust system, readying the combustion chamber for the next intake cycle.
"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.