Evinrude 4906B 4HP 1969, Owner'S Manual

Page: 28 / 422

5- Check the carburetor adjustments
and the need for an overhaul. See Chap-
ter 4.
6- Check the fuel pump for adequate
performance and delivery. See Chapter
4.
7- Make a general inspection of the igni-
tion system. See Chapter 5.
8- Test the starter motor and the sole-
noid. See Chapter 6.
9- Check the internal wiring.
10- Check the synchronization. See
Chapter 5.
2-3 COMPRESSION CHECK
A compression check is extremely im-
portant, because an engine with low or un-
even compression between cylinders CAN-
NOT be tuned to operate satisfactorily.
Therefore, it is essential that any compres-
sion problem be corrected before proceeding
with the tune-up procedure. See Chapter 3.
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 the cylinders visually
thru the transfer ports for possible scoring.
A more thorough inspection can be made if
the head is removed. It is possible for a
cylinder with satisfactory compression to be
scored slightly. Also, check the water
pump. The overheating condition may be
caused by a faulty water pump.
Removing the spark plugs for inspection. Worn
plugs are one
of
the major contributing factors
to
poor
engine performance.
COMPRESSION CHECK 2-3
An overheating condition may also be
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. Such a practice will result in an
overheated condition in a matter of seconds.
It is interesting to note, the same operator
would never operate or allow anyone else to
run a large horsepower engine without water
circulating through the lower unit for cool-
ing. Bear-in-mind, the laws governing oper-
ation and damage to a large unit ALL apply
equally as well to the small engine.
Checking Compression
Remove the spark plug wires. ALWAYS
grasp the molded cap and pull it loose with a
twisting motion to prevent damage to the
connection. Remove the spark plugs and
keep them in ORDER by cylinder for evalua-
tion
later. Ground the spark plug leads to
the engine to render the ignition system
inoperative while performing the compres-
sion check.
Insert a compression gauge into the
No.1, top, spark plug opening. Crank the
engine with the starter, or pull on the
starter cord, thru at least 4 complete
strokes with the throttle at the wide-open
position, or until the highest possible read-
ing is observed on the gauge. Record the
reading. Repeat the test and record the
compression for each cylinder. A variation
A compression check should be. taken in each cylin-
der before spending time and money on tune-up work.
Without adequate compression, efforts in other areas
to
regain engine performance will be wasted.