Evinrude 4906B 4HP 1969, Руководство пользователя

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5-2 IGNITION
5-2 SPARK PLUG EVALUA TION
Removal: Remove the spark plug wires
by pulling and twisting on only the molded
cap. NEVER pull on the wire or the connec-
tion inside the cap may become separated or
the boot damaged. Remove the spark plugs
and keep them in order. TAKE CARE not to
tilt the socket as you remove the plug or the
insulator
may be cracked.
Examine: Line the plugs in order of
re moval and carefull y examine the m to de-
termine the firing conditions in each cylin-
der. If the side electrode is bent down onto
the center electrode, the piston is traveling
too far upward in the cylinder and striking
the spark plug. Such damage indicates the
wrist pin or the rod bearing is worn exces-
sively. In all cases, an engine overhaul is
required to correct the condition. To verify
the cause of the problem, turn the engine
over by hand. As the piston moves to the
full up position, push on the piston crown
with a screwdr iver inserted through the
spark plug hole, and at the same time rock
the flywheel back-and-forth. If any play in
the piston
is
detected, the engine must be
rebuilt.
Correct Color: A proper firing plug
should be dry and powdery. Hard deposits
inside the shell indicate too much
oil
is
being mixed with the fuel. The most import-
ant
evidence is the light gray color of the
porcelain, which is an indication this plug
has been running at the correct tempera-
ture. This means the plug is one with the
correct heat range and also that the air-fuel
mixture is correct.
Rich Mixture: A black, sooty condition
This spark plug is foul from operating with an over-
rich condition, possibly an improper
carburetor
adjust-
ment.
Damaged spark plugs. Notice the broken electrode
on the left plug. The broken part MUST be found and
removed
before returning the engine
to
service.
on both the spark plug shell and the porce-
lain
is
caused by an excessively rich air-fuel
mixture, both at low and high speeds. The
rich mixture lowers the combustion temper-
ature so the spark plug does not run hot
enough to burn off the deposits.
Deposits formed only on the shell is an
indication the low-speed air-fuel mixture is
too rich. At high speeds with the correct
mixture, the temperature in the combustion
chamber is high enough to burn off the
deposits on the insulator.
Too Cool: A dark insulator, with very
few deposits, indicates the plug is running
too cool. This condition can be caused by
low compression or by using a spark plug of
an incorrect heat range. If this condition
shows on only one plug it is most usually
caused by low compression in that cylinder.
If all of the plugs have this appearance, then
it
is probably due to the plugs having a too-
low heat range.
This spark plug has been operating too-cool, because
it is rated with a too-low heat range for the engine.