Manual Yamaha XV920 Virago (page 362 of 363) (English)

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Common spark plug conditions

NORMAL

Symptoms: Brown to grayish-tan color and slight

electrode wear. Correct heat range for engine and

operating conditions.

Recommendation: When new spark plugs are

installed, replace with plugs of the same heat range.

WORN

Symptoms: Rounded electrodes

with a small amount of deposits on

the firing end. Normal color. Causes

hard starting in damp or cold

weather and poor fuel economy.

Recommendation: Plugs have

been left in the engine too long.

Replace with new plugs of the

same heat range. Follow the rec-

ommended maintenance schedule.

CARBON DEPOSITS

Symptoms: Dry sooty deposits

indicate a rich mixture or weak igni-

tion. Causes misfiring, hard starting

and hesitation.

Recommendation: Make sure the

plug has the correct heat range.

Check for a clogged air filter or

problem in the fuel system or

engine management system. Also

check for ignition system problems.

ASH DEPOSITS

Symptoms: Light brown deposits

encrusted on the side or center

electrodes or both. Derived from oil

and/or fuel additives. Excessive

amounts may mask the spark,

causing misfiring and hesitation

during acceleration.

Recommendation: If excessive

deposits accumulate over a short

time or low mileage, install new

valve guide seals to prevent seep-

age of oil into the combustion

chambers. Also try changing gaso-

line brands.

OIL DEPOSITS

Symptoms: Oily coating caused

by poor oil control. Oil is leaking

past worn valve guides or piston

rings into the combustion chamber.

Causes hard starting, misfiring and

hesitation.

Recommendation: Correct the

mechanical condition with neces-

sary repairs and install new plugs.

GAP BRIDGING

Symptoms: Combustion deposits

lodge between the electrodes.

Heavy deposits accumulate and

bridge the electrode gap. The plug

ceases to fire, resulting in a dead

cylinder.

Recommendation: Locate the

faulty plug and remove the deposits

from between the electrodes.

TOO HOT

Symptoms: Blistered, white insu-

lator, eroded electrode and

absence of deposits. Results in

shortened plug life.

Recommendation: Check for the

correct plug heat range, over-

advanced ignition timing, lean fuel

mixture, intake manifold vacuum

leaks, sticking valves and insuffi-

cient engine cooling.

PREIGNITION

Symptoms: Melted electrodes.

Insulators are white, but may be

dirty due to misfiring or flying

debris in the combustion chamber.

Can lead to engine damage.

Recommendation: Check for the

correct plug heat range, over-

advanced ignition timing, lean fuel

mixture, insufficient engine cooling

and lack of lubrication.

HIGH SPEED GLAZING

Symptoms: Insulator has yellow-

ish, glazed appearance. Indicates

that combustion chamber temper-'

atures have risen suddenly during

hard acceleration. Normal deposits."

melt to form a conductive coating.

Causes misfiring at high speeds.

Recommendation: Install new

plugs. Consider using a colder plug

if driving habits warrant.

DETONATION

Symptoms: Insulators may be

cracked or chipped. Improper gap

setting techniques can also result

in a fractured insulator tip. Can lead

to piston damage.

Recommendation: Make sure the

fuel anti-knock values meet engine

requirements. Use care when set-

ting the gaps on new plugs. Avoid

lugging the engine.

MECHANICAL DAMAGE

Symptoms: May be caused by a

foreign object in the combustion

chamber or the piston striking an

incorrect reach (too long) plug.

Causes a dead cylinder and could

result in piston damage.

Recommendation: Repair the

mechanical damage. Remove the

foreign object from the engine

and/or install the correct reach

plug.

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Yamaha XV920 Virago Manual

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