Operating At High Elevations; Engine Break-In Procedure - Mercury 25 Series Owner's Manual

If you keep your boat moored in the water, always tilt the outboard
so the gearcase is completely out of water (except in freezing
temperatures) when not in use.
Wash the outboard exterior and flush out the exhaust outlet of the
propeller and gearcase with fresh water after each use. Each
month, spray Mercury Precision or Quicksilver Corrosion Guard on
external metal surfaces. Do not spray on corrosion control anodes
as this will reduce the effectiveness of the anodes.

Operating at High Elevations

IMPORTANT: To prevent serious damage to the engine caused
by a lean fuel mixture, do not operate your outboard (if the jets were
changed for high elevation) at a lower elevation unless the jets are
changed again to correspond to the new elevation.
Operating your outboard at an elevation higher than 750 m
(2500 ft.) above sea level may require a carburetor jet change and/
or different pitch propeller. Consult your dealer. This will reduce
the normal performance loss experienced as a result of reduced
oxygen in the air causing an overly rich fuel mixture.
Engine Break‑in Procedure
IMPORTANT: Failure to follow the engine break‑in procedures can
result in poor performance throughout the life of the engine and
can cause engine damage. Always follow break‑in procedures.
Break-in running time: 10 hours
Time 0 min.~
Method of Trolling or
break‑in
Cruising at
Running
minimum
conditions
ENGINE BREAK-IN FUEL MIXTURE
Use a 25:1 gasoline/oil mixture in the first tank of fuel.
OPERATION
10 min.~
Throttle
opening
<1/2
idling about
3,000
RPM
—
speed
1 hr.~
Throttle
opening <3/4
about 4,000
RPM
Full‑throttle
run is allowed
for 1 min. in
10 min.
63
2 hrs.~ 10 hrs.~
Throttle
opening 3/4 Normal
about 4,000 running
RPM
Full‑throttle
run is allowed
for a short
time.
—