Spark Plug Inspection And Replacement - Mercury 4 Manual

8. Place a block of wood between gearcase and propeller to prevent rotation and tighten propeller nut. Secure
propeller nut to the shaft with cotter pin.
a - Cotter pin
b - Propeller nut
c - Rear thrust hub

Spark Plug Inspection And Replacement

Avoid serious injury or death from fire or explosion caused by damaged spark plug boots. Damaged spark plug
boots can emit sparks. Sparks can ignite fuel vapors under the engine cowl. To avoid damaging spark plug
boots, do not use any sharp object or metal tool such as pliers, screwdriver, etc. to remove spark plug boots.
1. Remove the spark plug boot. Twist the rubber boot slightly and pull off.
2. Remove the spark plug to inspect. Replace spark plug if electrode is worn or the insulator is rough, cracked,
broken, blistered or fouled.
3. Set the spark plug gap to specification.
MAINTENANCE
a
b
c
d
WARNING
!
e
d - Propeller
e - Front thrust washer
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