Evinrude 4906B 4HP 1969 Owner's Manual page 169

5-10
IGNITION
not available, hold the plug wire about 1/4-
inch from the engine.
with a pull starter or electrical
check for spark. A strong spark over a wide
gap must be observed when testing in this
manner, because under compression a strong
spark is necessary in order to ignite the air-
fuel mixture in the cylinder.
is possible to think you have a strong spark,
when in reali ty the spark will be too weak
when the plug is installed.
spark, or if the spark is weak, the trouble is
most likely under the flywheel in the mag-
neto.
ONE MORE WORD:
its own ignition system in a flywheel-type
ignition system. This means if a strong
spark is observed on anyone
not at another, only the weak system is at
fault. However, it is always a good idea to
check and service
flywheel is removed.
Compression
A compression
portant, because an engine with low or un-
even compression between cylinders
be tuned to operate
NOT
and
Checking the rings
opening on the exhaust side
are and
walls not scored
piston (fail to expand properly).
Turn the flywheel
starter
This means it
If there is no
Each cylinder
cylinder and
all systems while the
check is extremely
CAN-
satisfactorily.
cylinder walls through
of the engine to be mre the
the rings are not stuck in the
Therefore,
sion problem be corrected before proceeding
and with the tune-up procedure. See Chapter 3.
If the power head shows any indication of
overheating,
paint, especially in the area of the top (No.
L) cylinder,
thru the transfer ports for possible scoring.
A more thorough inspection can be made if
the head is
cylinder with satisfactory
scored slightly.
pump. The overheating
caused by a faulty water pump.
has An overheating
caused by running the engine out of the
water. For unknown reasons, many opera-
tors have formed a bad habit of running a
small engine without the lower unit being
submerged.
overheated
It is interesting
would never operate or
run a large horsepower engine without water
im- circulating
ing. Bear-in-mind, the laws governing oper-
ation and damage to a large unit
equally as well to the small engine.
preferred
The
the
and rings is
This method
each cylinder.
it is essential that any compres-
such as discolored or scorched
inspect the cylinders
removed. It is possible for a
compression to be
Also, check
condition
condition
Such a practice will result in a
condition in a matter of seconds.
to note, the same operator
allow
through the lower unit for cool-
of
method checking the cylinder
to
pull the head and make an inspection.
will also reveal the piston
visually
the water
may be
may also be
anyone else to
ALL apply
walls
condition in