Operating At High Elevations; Engine Break-In Procedure; Starting The Engine - Mercury 75 TwoStroke Operation, Maintenance & Installation Manual

• Change gear ratio.
Some boat performance can be improved by dropping to a lower pitch
propeller, but engine performance will still remain lower. In some cases, a gear
ratio reduction may be more beneficial. To optimize engine performance, prop
the engine to allow it to operate at or near the top end of the recommended
maximum RPM range at wide‑open throttle with a normal boat load.
Other advantages to propeller or gear ratio changes:
• Reduces the possibility of detonation
• Enhances overall reliability and durability of the engine

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.
MODELS WITH OIL INJECTION
Engine Break‑in Fuel Mixture ‑ Use a 50:1 (2%) gasoline/oil mixture in the
first tank of fuel. Use of this fuel mixture combined with oil from the oil injection
system will supply adequate lubrication during engine break‑in.
Engine Break‑in Procedure ‑ Vary the throttle setting during the first hour of
operation. During the first hour of operation, avoid remaining at constant speed
for more than two minutes and avoid sustained wide‑open throttle.
MODELS WITHOUT OIL INJECTION
Engine Break‑in Fuel Mixture ‑ Use a 25:1 (4%) gasoline/oil mixture in the
first tank of fuel. After the break‑in fuel mixture is used up, use a 50:1 (2%)
gasoline/oil mixture.
Engine Break‑in Procedure ‑ Vary the throttle setting during the first hour of
operation. During the first hour of operation, avoid remaining at constant speed
for more than two minutes and avoid sustained wide‑open throttle.

Starting the Engine

Before starting, read the Prestarting Check List, special operating
instructions, and Engine Break‑in Procedure in the Operation section.
OPERATION
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