Normal Condition; Carbon-Fouled; Oil-Fouled; Gap Bridging - Polaris 1999 Sportsman 400 Service Manual

L UBR ICATION, MAINTENANCE AND TU NE-UP 87
era te the ATV at the load that correspo nds to the
jetting information desired. For example, if the
ma in j et is in qu estio n, operate the ATV at fu ll throt-
tle and shut the engine off and coast to a stop.
Nor mal condition
If the plug has a light tan- or g ray-c o lor ed dep osit
and no abnormal gap
wear
or eros ion, good engine,
air/fuel mixture and ignition condition are indi-
cated . The plu g in use is o f th e proper heat ran ge and
may be serviced and returned
10
use.
Carbon-f ouled
SoO, dry, sooty deposits covering the entire firing
end
or
the plug are ev idence of incomplctc combus-
tion. Even though the tiring end of the plug is dry,
the plug 's insulation decreases when in this condi-
tion. An elec trical path is formed that bypasses the
electrodes resulting in a misfire condition. One or
more of the following can cause carbon fouling:
I. Too rich fuel mixture.
2. Spa rk plug heat range too co ld.
3. C logged air fihcr,
4. Improperly operating ignition component.
5. Ignition compone nt failure .
6. Low engine compression.
7. Pro lo nge d idli ng.
Oil-f Ol d ed
T he tip of an oi l-foule d plug has a black insulato r
tip, a damp oily film overthe firing end anda carbon
layer over the entire nose. The electrodes are not
worn. Common causes for this condition arc:
I. Incorrect a ir/fu e l m ixt ure .
2. Low idle speed or pro longed id ling.
3. Ignition component failure.
4. S park pl ug heat ra nge too co ld.
5. Eng ine still bein g broken in.
6. Va lve guides worn.
7.
Piston rings
\V 0 111
or broken.
An o il-fo uled spark plug may be cleaned in an
eme rge ncy, but it is be tter to rep lace it.
It
is impor-
tant to correct the cause
of fouling
before the engine
is returned to service.
Gap bridging
Plugs with this condition exhibit gaps shorted out
by
combustion deposits between the electrodes. If
this condition is encountered, check for excessive
carbon or oil in the combustion chamber. Be sureto
locate and correct the cause of this condition.
Badly worn electrodes and premature gap wear
arc signs of overheating, along with a grayor
wh ite
blistered porcelain insulator surface. The most
common cause for this condition is using a spark
plug of the wrong heat range (too hot). If a hotter
plug has not been installed and the plug is over-
heated, consider the following causes:
I. Lean air/fuel mixture.
2.
Improperly operating ignition component.
3. Engine lubrication
syste m ma lfun ction,
4. Cooling system malfunction.
5. Engine
air leak.
6. Improperspark plug installation (overt ightening).
7. No spark plug gas ket.