Ski-Doo FORMULA S 1997, Shop Manual

Page: 193 / 926

Section 05 ELECTRICAL
Sub-Section 04 (SPARK PLUGS)
05-04-3
DISASSEMBLY
First unscrew the spark plug 1 turn.
Clean the spark plug and cylinder head with pres-
surize air then completely unscrew.
WARNING : Whenever using compressed
air, always wear protective eye wear.
HEAT RANGE
The proper operating temperature or heat range
of the spark plugs is determined by the spark plug
ability to dissipate the heat generated by combus-
tion.
The longer the heat path between the electrode
tip to the plug shell, the hotter the spark plug op-
erating temperature will be – and inversely, the
shorter the heat path, the colder the operating
temperature will be.
A “cold” type plug has a relatively short insulator
nose and transfers heat very rapidly into the cylin-
der head.
Such a plug is used in heavy duty or continuous
high speed operation to avoid overheating.
The “hot” type plug has a longer insulator nose
and transfers heat more slowly away from its fir-
ing end. It runs hotter and burns off combustion
deposits which might tend to foul the plug during
prolonged idle or low speed operation.
1. Cold
2. Hot
CAUTION : Severe engine damage might
occur if a wrong heat range plug is used.
A too “hot” plug will result in overheating and pre-
ignition, etc.
A too “cold” plug will result in fouling (shorting
the spark plug) or may create carbon build up
which can heat up red-hot and cause pre-ignition
or detonation.
FOULING
Fouling of the spark plug is indicated by irregular
running of the engine, decreased engine speed
due to misfiring, reduced performance, and in-
creased fuel consumption. This is due to a loss of
compression. Other possible causes are : pro-
longed idling, or running on a too rich mixture due
to a faulty carburetor adjustment or incorrect fuel
and/or fuel mixing. The plug face of a fouled spark
plug has either a dry coating of soot or an oily,
glossy coating given by an excess either of oil or
of oil with soot. Such coatings form a conductive
connection between the center electrode and
ground.
SPARK PLUG ANALYSIS
1. Overheated (light grey)
2. Normal (brownish)
3. Fouled (black)
The plug electrode (and piston dome) reveals the
condition of the engine, operating condition,
method of driving and fuel mixture. For this rea-
son it is advisable to inspect the spark plug at reg-
ular intervals, examining the plug electrode and
the piston dome.
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