Yamaha MM700A Manual page 83

LUBRICATION, MAINTENANCE AND TUNE-UP
Too short Correct
cult to remove without damaging threads in
the cylinder head.
5. Attach the spark plug wires. Make sure they snap onto
the top of the plugs tightly.
Make sure the spark plug wire is located
Reach
Too long
Reading Spark Plugs
Because the firing end of a spark plug operates in the
combustion chamber, it reflects the operating condition of
the engine. Much information about engine and spark
plug performance can be determined by careful examina-
tion of the spark plug. Refer to Figure 35.
Normal condition
If the plug has a light tan- or gray-colored deposit and
no abnormal gap wear or erosion, good engine, earbure-
proper heat range and may be serviced and returned to
use.
Carbon fouled
Soft, dry, sooty deposits covering the entire firing end
of the plug are evidence of incomplete combustion. Even
though the firing end of the plug is dry. the plug's insula-
tion decreases. An electrical path is formed that lowers the
voltage from the ignition system. Engine misfiring is a
sign of carbon fouling. Carbon fouling can be caused by
one or more of the following:
1. Rich fuel mixture.
2. Cold spark plug heat range.
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