Heat Range; Normal Condition - Yamaha V star 1100 Owner's Manual

64
the spark plug post. If the cap does not
completely contact the plug, the en
gine may falter and cut out at high en
gine speeds.
6. Install each plug cap onto the correct spark plug.
Press the cap onto the spark plug and rotate the as-
sembly slightly in both directions. Make sure it is
attached to the spark plug and to the sealing surface
of the cylinder head cover.
7. Install the cylinder head cover as described in
Chapter Four.

Heat Range

Spark plugs are available in various heat ranges
that are hotter or colder than the plugs originally in-
stalled by the manufacturer.
Select a plug with a heat range designed for the
loads and conditions under which the motorcycle
will be operated. A plug with an incorrect heat
range can foul, overheat and cause piston dam-
age.
In general, use a hot plug for low speeds and low
temperatures. Use a cold plug for high speeds, high
engine loads and high temperatures. See Figure 23.
The plug should operate hot enough to burn off un-
wanted deposits, but not so hot that it is damaged or
causes preignition. To determine if plug heat range
is correct, remove each spark plug and examine the
insulator.
Do not change the spark plug heat range to com-
pensate for adverse engine or carburetion condi-
tions.
When replacing plugs, make sure the reach (Fig-
ure 24) is correct. A longer than standard plug
could interfere with the piston and cause engine
damage.
Refer to Table 5 for recommended spark plugs.
Reading
Reading the spark plugs can provide information
about spark plug operation, air/fuel mixture compo-
sition and engine conditions (such as oil consump-
tion or pistons). Before checking the spark plugs,
operate the motorcycle under a medium load for ap-
proximately 6 miles (10 km). Avoid prolonged
idling before shutting off the engine. Remove the
spark plugs as described in this section. Examine
23
HOT
TYPE
24
Correct
Too long
each plug and compare it to those in Figure 25.
Refer to the following sections to determine the op-
erating conditions.
If the plugs are being inspected to determine if
carburetor jetting is correct, start with new plugs
and operate the motorcycle at the load that corre-
sponds to the jetting information desired. For exam-
ple, if the main jet is in question, operate the
motorcycle at full throttle, shut the engine off and
coast to a stop.

Normal condition

A light tan- or gray-colored deposit on the firing
tip and no abnormal gap wear or erosion indicate
good engine, ignition and air/fuel mixture condi-
tions. A plug with the proper heat range is being
used. It may be serviced and returned to use.
CHAPTER THREE
COLD
TYPE
Too short