Mercury 75 Operation Maintenance Warranty Installation Manual page 103

1. Remove the spark plug leads by twisting the rubber boots while pulling
them off the spark plugs.
2. 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
3. Set the spark plug gap. Refer to 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.
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