Used Spark Plug Analysis - Mercury MerCruiser MCM 454 Mag MPI Service Manual

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SERVICE MANUAL NUMBER 23
DO NOT run engine above 1500 rpm, as suction created by seawater pickup pump
may collapse water supply hose and cause engine to overheat.
Be sure that engine compartment is well ventilated and that no gasoline vapors are
present to prevent the possibility of a FIRE or EXPLOSION.
DO NOT leave helm unattended while performing idle speed adjustment.

Used Spark Plug Analysis

Use the following illustrations for determining serviceability of spark plug. Spark plug
condition also can suggest a variety of possible engine malfunctions and, therefore, can
indicate needed engine repairs. When old plugs are replaced, replace entire set. Perform
plug service only on those plugs suitable for additional service, using the following
procedures:
1. Remove any oil deposits with solvent and dry plugs thoroughly.
2. Open electrode gap wide enough to permit cleaning and filing.
3. Remove combustion deposits from firing end of spark plug with a plug cleaner. Blow off
4. Reset gap to specifications by bending only side electrode with proper tool.
Index
Index
90-861326--1 MARCH 1999
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with compressed air to remove abrasives.
CAUTION
WARNING
WARNING
TROUBLESHOOTING
Page 1C-3

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