Engine Runs Erratically; Engine Over-Speed (Excessive Rpm); Performance Loss - Mercury 25 Jet 4-Stroke Manual

• Spark plugs fouled or defective. Refer to Maintenance section.

Engine Runs Erratically

POSSIBLE CAUSES
• Overheating ‑ Warning horn not working.
• Low oil pressure. Check oil level.
• Spark plugs fouled or defective. Refer to Maintenance section.
• Incorrect setup and adjustments.
• Fuel is being restricted to the engine.
a. Engine fuel filter is obstructed. Refer to Maintenance
section.
b. Fuel tank filter obstructed.
c. Stuck anti‑siphon valve located on permanently built‑in
type fuel tanks.
d. Fuel line is kinked or pinched.
• Fuel pump failure.
• Ignition system component failure.
Engine Over‑Speed (Excessive RPM)
POSSIBLE CAUSES
• Outboard mounted too high on the transom.
• Worn jet pump impeller or liner.
• Incorrect jet pump impeller clearance adjustment.
• Tilting the outboard out beyond a vertical position.
• Cavitation of the impeller due to rough water or obstruction in
the boat hull.
• Blockage of the water intake.

Performance Loss

POSSIBLE CAUSES
• Throttle not fully open.
• Damaged impeller.
• Incorrect engine timing, adjustments, or setup.
• Boat overloaded or load improperly distributed.
TROUBLESHOOTING
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