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MerCruiser Sterndrive 4.3 MPI User Manual

MerCruiser Sterndrive 4.3 MPI
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Section 3 - On The Water
Page 54 90-864195070 JUNE 2007
Improves ease of planing
Improves rough water ride
At extremes, can cause the boat to veer back and forth (bow steer)
Bottom Of Boat
To maintain maximum speed, the boat bottom should be:
Clean, free of barnacles and marine growth
Free of distortion; nearly flat where it contacts the water
Straight and smooth, fore and aft
Marine vegetation may accumulate when the boat is docked. This growth must be removed
before operation; it may clog the water inlets and cause the engine to overheat.
Cavitation
Cavitation occurs when water flow cannot follow the contour of a fast‑moving underwater
object, such as a gear housing or a propeller. Cavitation permits the propeller to speed up,
but the boat speed to reduce. Cavitation can seriously erode the surface of the gear housing
or the propeller. Common causes of cavitation are:
Weeds or other debris snagged on the propeller
Bent propeller blade
Raised burrs or sharp edges on the propeller
Ventilation
Ventilation is caused by surface air or exhaust gases that are introduced around the
propeller resulting in propeller speed‑up and a reduction in boat speed. Air bubbles strike
the propeller blade and cause erosion of the blade surface. If allowed to continue, eventual
blade failure (breakage) will occur. Excessive ventilation is usually caused by:
Drive unit trimmed out too far.
A missing propeller diffuser ring.
A damaged propeller or gear housing, which allows exhaust gases to escape between
propeller and gear housing.
Drive unit installed too high on transom.
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.

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MerCruiser Sterndrive 4.3 MPI Specifications

General IconGeneral
BrandMerCruiser
ModelSterndrive 4.3 MPI
CategoryEngine
LanguageEnglish

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