Marine Power BASE Series Manual page 6

3.
Precautions/Instructions
Water Can Enter the Engine Cylinders
Through the Intake or Exhaust System.
Beware of these situations:
1. Following Wakes: Sudden slow-downs may cause the
boat wake to flow over the transom of your boat. Most
engine hatch covers are not watertight. Water spilling
into the engine compartment can easily enter the air in-
take, especially if the engine is running.
2. Engine Shutdown: Sudden engine shutdown while the
boat is moving may force water into the exhaust system.
3. Improper Installation: Refer to exhaust pipe section. An
exhaust system without flappers and the specified incline
increases the likelihood of water entering the engine.
4. Improper Hoisting: Operators are sometimes tempted to
reduce hoisting time for propeller changes by hoisting
only the boat stern. Such hoisting can cause residual wa-
ter in the exhaust system to enter engine cylinders.
Water entering engine cylinders will cause the engine to lock
because water does not compress. To remedy this situation,
take the following steps:
1. Change engine oil and filters.
2. Remove all spark plugs.
3. Remove coil wire.
4. Crank engine for 15 seconds.
5. Replace spark plugs and reattach coil wire.
6
6. Start engine - if there are any abnormal sounds STOP
ENGINE immediately and contact your MARINE POWER
dealer.
Water Inversion
Water inversion is water that is pulled back into the exhaust
which usually ends up in the piston cylinder. Most of the time
this happens under the following conditions:
• Shutting off engine at high RPM's.
• Water comes up the exhaust after a quick slowdown.
• Long periods of idling.
• Exhaust drop not sufficient.
Usually the water is not found until the next time the boat is
used. In some cases, this may not be for weeks. In the case
of a salt water environment this is catastrophic due to the
rusting.
To minimize the problem MARINE POWER requires the instal-
lation of flappers at the transom and in the exhaust hose just
after the exhaust riser or elbow.
Detonation and/or Pre-Ignition
Detonation is most commonly known as "pinging", "spark
knock" or "fuel knock". It is the abnormal combustion of the
fuel which causes the fuel to explode severely within the
combustion chamber.
In a four-cycle engine, normal combustion or burning starts
at the spark plug and a wave of flames move across the
combustion chamber. This results in an even pressure rise in
the combustion chamber which pushes the piston downward.
Detonation begins as normal combustion with the spark-
ignited flame progressing across the combustion chamber
while applying the heat and pressure to the unburned portion
of fuel. Instead of continuing to burn evenly, the last portion of
the fuel explodes violently which in turn cases overheating of
the pistons, valves and spark plugs.
This may occur at any speed and is not often detected, serious
and tragic engine damage may occur.
There are many causes of detonation, with the most common
being the use of a low-octane gasoline or improperly timed
ignition. Detonation may also occur when using the proper
octane gasoline if engine maintenance has been neglected.
Possible causes include:
1. Poor or improper fuel quality/octane.
2. Improper initial ignition timing setting.
3. Improper propeller selection.
4. Engine overload, such as operating twin-engine boat with
only one engine.
5. Improper cooling operation resulting in engine overheating.
6. Fuel starvation or vapor lock resulting from poor fuel
quality/lean out.
7. Malfunctioning carburetor causing lean mixture.
8. Operating engine that is out of proper tune, dead cylinder,
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