Evinrude 4906B 4HP 1969 Owner's Manual page 29

2-4 TUNING
Damaged spark plugs.
on the left plug. The broken part must be found and
removed before returning
between cylinders is far more important
than the actual readings.
more than 5 psi between cylinders indicates
the lower compression cylinder may be de-
fective. The problem may be worn, broken,
or sticking piston rings, scored pistons or
worn cylinders. These problems may only be
determined after the head has been remov-
ed. Removing the head on an outboard
engine is not that big a deal and may save
many hours of frustration
purchasing unnecessary
faulty condition.
2-4 SPARK PLUG INSPECTION
Inspect each spark plug for badly worn
electrodes, glazed, broken, blistered, or lead
fouled insulators. Replace all of the plugs,
if one shows signs of excessive wear.
Make an evaluation
formance by comparing the spark condition
with those shown in Chapter 5. Check each
spark plug to be sure they are all of the
same manufacturer
range rating.
FOULED
ELECTRODES
A foul spark plug.
indicates problems in the cylinder
rected.
Notice the broken electrode
to
the engine service.
A variation
and the cost of
parts to correct
of the cylinder per-
and have the same heat
The condition of this plug
that should be cor-
Inspect
opening of the head and clean the threads
before installing the plug. If the threads are
damaged, the head should be removed and
and a Hell-coil insert installed.
tempt is made to drill out the opening with
the head in place, some of the filings may
fall into the cylinder and cause damage to
the cylinder wall during operation.
the head is made of aluminum, the filings
cannot be removed with a magnet.
When purchasing
WAYS ask the marine dealer if there
been a spark plug change for the engine
being serviced.
Crank the engine through several revo-
of lutions to blowout
might have become dislodged during clean-
mg.
Install the spark plugs and tighten them
to a torque value of 17 ft-lbs.
a new gasket and wipe the seats in the block
clean. The gasket must be fully compressed
on clean seats to complete the heat transfer
process and to provide a gas tight seal in the
cy Ii nder, If the torque value is too high, the
heat will dissipate too rapidly.
a
if the torque value is too low, heat will not
dissipate fast enough.
2- 5 IGNITION
Only one ignition
magneto, is used on outboard engines cover-
ed in this manual.
mance is less than expected,
tion is diagnosed as the problem area, refer
to Chapter
dures. To properly synchronize
system with the fuel system, see Chapter 5.
Today, numerous type spark plugs
ALWAYS
service.
to
be sure you are purchasing the proper plugs for the
engine being serviced.
the threads in the spark plug
new spark plugs,
any material
ALWAYS use
Conversely,
SYSTEM
system, a flywheel-
If the engine perfor-
and the igni-
5 for detailed service
the ignition
are
check with your local marine dealer
If an at-
Because
AL-
has
which
proce-
available for