Yamaha MM600D, Manual

Page: 83 / 282

LUBRICATION, MAINTENANCE AND TUNE-UP 77
Reach
Too short Correct
Too long
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
the exhaust pipe.
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
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,
and ignition condition are indicated. This plug is the
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
the ignition system. Engine misfiring is a
sign of carbon fouling. Carbon fouling can be by
one or more of the following:
1. Rich fuel mixture.
2.
Cold spark plug range.