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General Information
Elevation and Climate
Elevation and climate changes will affect the performance of your power package. Loss of performance can be caused by:
•
Higher elevations
•
Higher temperatures
•
Low barometric pressures
•
High humidity
For you to have optimum engine performance under changing weather conditions, it is essential that the engine be propped to
allow the engine to operate at or near the top end of the specified maximum RPM range with a normal boat load during your
normal boating weather conditions.
In most cases, recommended RPM can be achieved by changing to a lower pitch propeller.
Detonation
Detonation in a 4‑cycle engine resembles the pinging heard in an automobile engine. It can be otherwise described as a tin‑like
rattling or plinking sound.
Detonation is the explosion of the unburned fuel/air charge after the spark plug has fired. Detonation creates severe shock
waves in the engine. These shock waves often find or create a weakness: the dome of a piston, cylinder head or gasket, piston
rings or piston ring lands, piston pin, and roller bearings.
A few of the most common causes of detonation in a marine 4‑cycle application are as follows:
•
Over‑advanced ignition timing
•
Use of low octane gasoline
•
Propeller pitch too high: engine RPM below recommended maximum range
•
Lean fuel mixture at, or near, wide‑open throttle
•
Spark plugs: heat range too hot, incorrect reach, cross‑firing
•
Deteriorated or inadequate engine cooling system
•
Combustion chamber deposits: result in higher compression ratio
Detonation usually can be prevented if:
•
The engine is correctly set up
•
Regular maintenance is scheduled
Propeller Selection
IMPORTANT: The engines covered in this manual are equipped with an RPM rev‑limiter that is set to an upper RPM limit. This
limit, which is slightly above the normal operating range of the engine, helps prevent damage from excessive engine RPM.
Once the RPM returns to the recommended operating RPM range, normal engine operation resumes.
The boat manufacturer and the selling dealer are responsible for equipping the power package with the correct propeller. Refer
to Mercury Marine's web page https://www.mercurymarine.com/en/us/propellers/selector/#/step‑one.
Select a propeller that will allow the engine power package to operate at or near the top end of the recommended WOT
operating RPM range with a normal load.
If full‑throttle operation is below the recommended range, the propeller must be changed to prevent loss of performance and
possible engine damage. On the other hand, operating an engine above the recommended operating RPM range will cause
higher than normal wear and damage.
After initial propeller selection, the following common problems may require that the propeller be changed to a lower pitch.
•
Warmer weather and greater humidity cause a loss of RPM.
•
Operating in a higher elevation causes a loss of RPM.
•
Operating with a dirty boat bottom causes a loss of RPM.
•
Operating with increased load (additional passengers, pulling skiers) causes a loss of RPM.
For better acceleration, such as is needed for waterskiing, use the next lower pitch propeller. When not pulling skiers, do not
operate at full throttle when using the lower pitch propeller.
Following Complete Submersion
Engine Submerged While Running (Special Instructions)
When an engine is submerged while running, the possibility of internal engine damage is greatly increased. After the engine is
recovered, remove the spark plugs. If the engine fails to turn over freely when turning the flywheel, the possibility of internal
damage (bent connecting rod and/or bent crankshaft) exists. The powerhead must be disassembled for inspection.
Page 1C-12
© 2016 Mercury Marine
90-8M0105568 eng MARCH 2016
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