Spark Plug: Testing and Inspection

Spark Plugs (Original Equipment NGK Plugs Shown):

1. Inspect spark plugs for:

a. Incorrect gap.
b. Carbon deposits.
c. Cracked center electrode insulator.
d. Burned or worn electrodes.
e. Fouling.

2. Burned or worn electrodes may result from:

a. Excessive mileage.
b. Lean fuel mixture.
c. Advanced ignition timing.
d. Loose plug.
e. Plug heat range too high.
f. Insufficient engine cooling.

3. Plug fouling may result from:

a. Rich fuel mixture.
b. Retarded ignition timing.
c. Excessive oil consumption.
d. Incorrect plug gap.
e. Plug heat range too low.
f. Excessive idling / low speed running.
g. Clogged air filter element.
h. Faulty coil or ignition wires.

4. When replacing plugs, adjust gap to 0.043 - 0.067 in (1.1 - 1.7 mm) and torque to 10 - 13 ftlb (12.7 - 17.7 Nm).