Checking The Spark Plugs - Yamaha Vector RS90RX Owner's Manual

Periodic maintenance
EWS00090
WARNING
Do not drive the snowmobile with the
G
shroud or covers unfastened or re-
moved.
Keep your body and clothing away from
G
rotating parts when servicing the snow-
mobile with the shroud or covers re-
moved.
Do not touch the hot muffler and engine
G
during or immediately after operation.
ECS00370
CAUTION:
Make sure that all cables, leads, etc., are
routed properly before installing the
shroud and covers.
NOTE:
When installing the shroud and covers, be
sure to tighten all fasteners securely.
ESU11780

Checking the spark plugs

The spark plug is an important engine compo-
nent and is easy to inspect. The condition of
the spark plug can indicate the condition of
the engine.
Check the coloration on the white porcelain
insulator around the center electrode. The
ideal coloration at this point is a medium to a
light tan color for a snowmobile that is being
ridden normally. If a spark plug shows a dis-
tinctly different color, there could be some-
thing wrong with the engine. For example, a
very white center electrode porcelain color
could indicate an intake track air leak or car-
buretion problem for that cylinder. Do not at-
tempt to diagnose such problems yourself.
Instead, take the snowmobile to a Yamaha
dealer for inspection and possible repairs.
42
You should periodically remove and inspect
the spark plug because heat and deposits will
cause a spark plug to slowly break down and
erode. Consult a Yamaha dealer before
changing to a different type of spark plug.
Specified spark plug:
Manufacturer:
NGK
Model:
CR8E
Spark plugs are produced in several different
thread lengths. The thread length or reach is
the distance from the spark plug gasket seat
to the end of the threaded portion. If the reach
is too long, overheating and engine damage
may result. If the reach is too short, spark plug
fouling and poor performance may result. Al-
so, if the reach is too short, carbon will form on
the exposed threads resulting in combustion
chamber hot spots and thread damage. Al-
ways use a spark plug with the specified
reach.
Spark plug reach:
19.0 mm (0.75 in)
1. Spark plug gap
2. Spark plug reach
Before installing any spark plug, measure the
electrode gap with a wire thickness gauge
and adjust to specification.