Evinrude 4906B 4HP 1969 Owner's Manual page 28

5- Check the
and the need for an overhaul.
ter 4.
6- Check the fuel pump for adequate
performance and delivery.
4.
7- Make a general inspection of the igni-
tion system. See Chapter 5.
8- Test the starter
noid. See Chapter 6.
9- Check the internal wiring.
10- Check the
Chapter 5.
2-3 COMPRESSION CHECK
A compression check is extremely
portant, because an engine with low or un-
even compression between
NOT be tuned to operate
Therefore, it is essential that any compres-
sion problem be corrected
with the tune-up procedure.
If the powerhead shows any indication of
overheating, such as discolored or scorched
paint, especially in the area of the top (No.
l) cylinder, inspect
thru the transfer ports for possible scoring.
A more thorough inspection can be made if
the head is removed.
cylinder with satisfactory
scored slightly. Also, check
pump. The overheating
caused by a faulty water pump.
Removing the spark
of
plugs are one the major contributing
engine performance.
carburetor adjustments
See Chap-
See Chapter
motor and the sole-
synchronization.
cylinders CAN-
satisfactorily.
before proceeding
See Chapter 3.
the cylinders visually
It is possible for a
compression to be
the water
condition may be
plugs for inspection.
factors
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 allow anyone else to
run a large horsepower engine without water
circulating
See ing. Bear-in-mind,
ation and damage to a large unit ALL apply
equally as well to the small engine.
Checking Compression
im-
Remove the spark plug wires.
grasp the molded cap and pull it loose with a
twisting
connection.
keep them in ORDER by cylinder for evalua-
tion later.
the engine to render
inoperative
sion check.
Insert
No.1, top, spark plug opening.
engine with the
starter cord,
strokes with the throttle
position, or until
ing is observed on the gauge.
reading.
compression
A compression
der before
Worn
to Without adequate compression,
poor
regain engine performance
COMPRESSION CHECK
condition
Such a practice will result in an
condition in a matter of seconds.
to note, the same operator
through the lower unit for cool-
the laws governing oper-
motion to prevent
Remove the spark plugs and
Ground the spark plug leads to
the ignition system
while performing
a compression gauge
starter, or pull on the
thru at least
at the wide-open
the highest possible read-
Repeat the test and record the
for each cylinder.
check should be. taken
spending time and money on tune-up
efforts
will be wasted.
2-3
may also be
ALWAYS
damage to the
the compres-
into the
Crank the
4 complete
Record the
A variation
in
each cylin-
work.
in other areas to