Mercury 200 Verado FourStroke Operation And Maintenance Manual page 94

5. Remove the spark plugs. Replace the spark plug if the electrode is worn;
the insulator is rough, cracked, broken, or blistered; or if the precious
metal is not visible on the spark plug electrode.
IMPORTANT: The color of the plug may not accurately reflect its condition. To
accurately diagnose a faulty plug, inspect the precious metal on the plug's
electrode. If no precious metal is visible, replace the plug.
a - Precious metal
6. Set the spark plug gap. Refer to General Information ‑ Specifications.
a. All of the spark plugs should have the gap checked and corrected as
necessary before installation.
b. Measure the gap with a feeler gauge or pin gauge. Never use a
wedge‑type gap checking tool to inspect or to adjust the gap.
c. If an adjustment is necessary, do not pry or apply any force on the
center electrode. This is critical with any type of spark plug that has a
wear surface, such as platinum or iridium added to either the ground
electrode or the center electrode.
d. When it is necessary to widen the gap, use a tool that only pulls back
on the ground electrode without touching the center electrode, the
porcelain, or the wear portion of the ground electrode.
e. When it is necessary to close the gap, gently tap the plug ground
electrode on a hard surface.
MAINTENANCE
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