Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 24Get this manual
Serial Number Location The engine serial number is located on the lower starboard side of the engine blockA serial number is also located on
the starboard side of the swivel bracket
Rejetting Carburetors for High Altitude Operation
The carburetor jets installed at the factory are for engine operation at sea level through an elevation of 2500 ft(762m) above sea levelIf the engine is to be operated at an altitude higher than 2500 feet, it will be necessary to rejet the carburetorsRefer to SECTION 3AFuel System ", for proper jet selection and idle mixture adjustments
Timing Adjustment for High Altitude Operation
Advance idle timing 2- degrees to maintain specified ingear idle RPM Refer to SECTION 2CTiming, SynchronizingAdjustingfor procedure to readjust Throttle Position Sensor to increase idle timing