5-10
IGNITION
not available,
hold the plug wire about
1/4-
inch from
the
engine.
Turn the
flywheel
with a pull starter
or electrical
starter
and
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.
This means it
is possible to think you have a strong spark,
when in reali ty the spark will be too weak
when the plug is installed.
If there
is no
spark, or if the spark is weak, the trouble
is
most likely under the flywheel
in the mag-
neto.
ONE MORE WORD:
Each
cylinder
has
its
own ignition
system
in a flywheel-type
ignition
system.
This
means
if a strong
spark
is observed
on anyone
cylinder
and
not at another,
only the weak system
is at
fault.
However,
it is always a good idea to
check
and
service
all
systems
while
the
flywheel is removed.
Compression
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.
Checking
the
rings
and
cylinder
walls
through
the
opening on the exhaust side
of
the engine
to be
mre
the
walls
are
not scored
and
the rings are not stuck
in the
piston (fail
to
expand properly).
Therefore,
it is essential
that
any compres-
sion problem be corrected
before proceeding
with the tune-up procedure.
See Chapter
3.
If the power head 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.
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 a
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.
The
preferred
method
of
checking
the cylinder
walls
and rings
is
to
pull
the
head and make
an inspection.
This
method
will
also
reveal
the
piston
condition
in
each cylinder.
Summary of Contents for 4906B 4HP 1969
Page 5: ......
Page 87: ...3 46 POWERHEAD Exploded drawing of a 7 5 hp powerhead 1956 58 with principle parts identified...
Page 88: ...CYLINDER BLOCK 3 47 HEAD GASKET RING...
Page 90: ...CYLINDER BLOCK 3 49 THERMOSTAT EXHAUST COVER The...
Page 137: ...4 46 FUEL LEVER AND LOW SPEED...
Page 153: ...4 62 FUEL Exploded view of a pressure tyoe fuel tank with major parts identified...
Page 157: ...4 66 fUEL...
Page 412: ...A 16 APPENDIX Wire Identification 33 hp with Generator 1965 67...
Page 413: ...APPENDIX A 17 o C...
Page 414: ...Wire Identification 33 hp with Generator 1969 70...
Page 415: ...APPENDIX A 19 Wire Identification 35 hp 1957 59...
Page 416: ...A 20 APPENDIX Wire Identification 40 hp Standard Shift with Generator 1960 66...
Page 417: ...APPENDIX A 21 UJ cc b Wire Identification 40 hp Standard Shift with Generator 1967 68...
Page 419: ...APPENDIX Wire Identification 40 hp Electric Shift with Generator 1961 66 A 23...
Page 420: ...A 24 APPENDIX C 00 Wire Identification 40 hp Electric Shift with Generator 1967 68...
Page 421: ...Wire Identification 40 hp Electric Shift with Generator 1969 70...
Page 422: ...NOTES NUMBERS...
