1-27
SPARK PLUGS
INSPECTION
Check spark plugs:
● Inspect at every 5000 mile (8000 km) service interval.
● Replace every 10,000 mile (16,000 km) service interval.
1. Disconnect cables from both spark plugs.
2. Remove spark plugs.
3. See Figure 1-37. Compare your observations of the plug
deposits with the descriptions provided below.
a. A wet, black and shiny deposit on plug base, elec-
trodes and ceramic insulator tip indicates an oil
fouled plug. The condition may be caused by one or
more of the following: worn pistons, worn piston
rings, worn valves, worn valve guides, worn valve
seals, a weak battery or a faulty ignition system.
b. A dry, fluffy or sooty black deposit indicates a carbu-
retor air-fuel mixture that is too rich, engine idling for
excessive periods of time and/or enrichener usage
for excessive periods of time.
c. A light brown, glassy deposit indicates an over-
heated plug. This condition may be accompanied by
cracks in the insulator or by erosion of the elec-
trodes and is caused by an air-fuel mixture that is
too lean, a hot-running engine, valves not seating or
improper ignition timing. The glassy deposit on the
spark plug is a conductor when hot and may cause
high-speed misfiring. A plug with eroded electrodes,
heavy deposits or a cracked insulator must be
replaced.
d. A plug with a white, yellow, tan or rusty brown pow-
dery deposit indicates balanced combustion. Clean
off spark plug deposits at regular intervals.
4. If the plugs require cleaning between tune-ups, proceed
as follows:
a. Degrease firing end of spark plug using ELECTRI-
CAL CONTACT CLEANER. Dry plug with com-
pressed air.
b. Use a thin file to flatten spark plug electrodes. A
spark plug with sharp edges on its electrodes
requires 25%-40% less firing voltage than one with
rounded edges.
5. If the plugs cannot be cleaned, replace with No. 6R12
spark plugs.
6. Check electrode gap with a wire-type feeler gauge. Gap
should be 0.038-0.045 in. (0.96-1.14 mm).
7. See Figure 1-38. Apply LOCTITE ANTI-SEIZE to plugs.
Install and tighten spark plugs to 11-18 ft-lbs (15-24 Nm).
8. Connect spark plug cables. Verify that cables are
securely connected to coil and spark plugs.
Figure 1-37. Typical Spark Plug Deposits
Figure 1-38. Spark Plugs
4636
5581
Tighten to 11-18
ft-lbs (15-24 Nm)
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