Mercury Mariner 4 and 5HP 4-Stroke Outboards Service Shop Manual 1999, Page 41Get this manual
OUTBOARD MOTOR INSTAL.L.ATION
Engine Over-Speed Protection System
The system is activated if the engine speed should ever exceed the maximum allowable limitThis will protect the engine from mechanical damageAnytime the engine over-speed system is activated, the system will automatically reduce the engine speed to within the allowable limitIf engine over-speed continueshave the outboard checked by your dealerNOTE: Your engine speed should never reach the maximum limit to activate the system unless the propeller is ventilating, an incorrect propeller is being used, or the propefler is faulty