Evinrude 4906B 4HP 1969 Owner's Manual page 162

Today, numerous type spark plugs are available
ALWAYS
service. check with your local marine dealer
to be
sure you are purchasing
engine being serviced.
Fouled: A fouled
caused by the wet
insulator shorting the high-tension
to ground inside the shell.
may also be caused
which prevent a high-tension
delivered to the spark plug.
Carbon Deposits:
posits are an indication
the fuel. This condition may be the result
of poor oil grade, (automotive-type
of a mar ine-type); improper oil-fuel mixture
in the fuel tank; or by worn piston rings.
Overheating: A dead white or gray insu-
lator, which is generally
indication of overheating
The electrode gap wear rate will be more
than normal and in the case of pre-ignition,
will actually cause the electrodes
CRACK
Cut-a-way drawing showing major spark plug parts.
for
the proper plug for the
spark plug may be
oily deposits on the
current
The condition
by ignition problems
pulse to be
Heavy carbon-like de-
of excessive oil in
instead
blistered, is an
and pre-ignition.
to melt as
POLARITY CHECK
shown in this illustration.
pre-ignition are usually caused by improper
point gap adjustment;
too-Iow an octane rating fuel; an excessive-
ly lean air-fuel mixture; or problems in the
cooling system.
Electrode Wear:
in a wide gap and if the electrode
carbonized it will form a high-resistance
path for the spark to jump across.
condition will cause the engine to misfire
during acceleration.
condition, it can cause an increase in fuel
consumption and very
during high-speed operation.
to replace the spark plugs with a rating in
the proper heat range and gapped to specifi-
cation.
Red rust-colored
firing end of a spark plug can be caused by
water in the cylinder combustion
This can be the first
entering the cylinders through the exhaust
manifold because of an accumulation
scale or defective
condition be corrected
MUST
opportunity. Refer
Service.
5-3 POLARITY CHECK
Coil polarity is extremely
proper battery ignition system operation.
a coil is connected
the spark plugs may demand from
percent more voltage to fire.
demand conditions, in a very short time the
coil would be unable to supply enough volt-
age to fire the plugs.
following three methods
quickly determine coil polarity.
1- The polar ity of the coil can be check-
ed using an ordinary D.C. voltmeter.
nect the positive lead to a good ground.
With the engine running, momentarily
the negative lead to a spark plug terminal.
Overheating and
detonation from using
Electrode wear results
becomes
Such a
If all plugs are in this
poor performance
The solution is
deposits on the entire
chamber.
evidence of water
exhaust shutter. This
at the first
to Chapter 3, Engine
important
with reverse polarity,
to
30
Under such
Anyone of the
may be used to
Con-
touch
5-3
of
for
If
4-0