How to Replace Spark Plugs in an Outboard Engine

Replacing spark plugs in your outboard engine is a quick and crucial maintenance task that ensures reliable starting, smooth performance, and better fuel efficiency.

Tools and Materials You’ll Need

  • New spark plugs (check your manual for type and gap)
  • Spark plug socket and ratchet
  • Torque wrench
  • Feeler gauge (if gaps need adjustment)
  • Anti-seize compound (optional)
  • Dielectric grease (optional)
  • Clean rag or compressed air
  • Gloves and safety glasses

Important Safety Tips Before You Begin

  • Turn off the engine and remove the safety lanyard before starting.
  • Work in a well-ventilated area away from open flames or sparks.
  • Wear gloves to protect your hands and avoid burns if the engine is warm.
  • Use only recommended spark plugs and proper torque specifications.

Step-by-Step Spark Plug Replacement

1. Locate the Spark Plugs

Open the engine cover and locate the spark plug wires. Most outboards have 2–6 plugs, depending on the number of cylinders.

Spark plugs location on an outboard engine

2. Clean Around the Spark Plug Area

Use a clean rag or compressed air to remove dirt and debris around the plugs to prevent contaminants from entering the cylinder.

3. Remove the Spark Plug Wires

Gently twist and pull the spark plug boots off the plugs. Do not pull on the wires themselves to avoid damage.

4. Remove the Old Spark Plugs

Using a spark plug socket and ratchet, turn the plugs counterclockwise to remove them. Note the condition of the old plugs for signs of engine issues.

Comparison of old and new spark plugs

5. Check and Adjust the New Plugs

Check the gap on the new plugs with a feeler gauge and adjust if necessary according to the manufacturer’s specs.

6. Install the New Plugs

Thread the new plugs in by hand to avoid cross-threading. Then tighten to the recommended torque with a wrench. Apply a small amount of anti-seize to threads if desired.

7. Reattach the Spark Plug Wires

Apply a dab of dielectric grease to the inside of the boots and push them firmly onto the plugs until they click or seat fully.

Spark plug wires connected to outboard engine

Pro Tips

  • Replace all spark plugs at the same time to maintain even performance.
  • Keep a spare set of plugs and a wrench onboard for emergencies.
  • Inspect wires and boots for wear or cracking while you’re at it.
💡 Pro Tip: Refer to your service manual for proper gap, torque specs, and the correct spark plug model for your specific outboard engine.

Conclusion

Replacing your outboard’s spark plugs regularly is simple and ensures smooth, dependable operation. Follow these steps and enjoy reliable starts every time.

If you need help finding the right service manual or spark plug specifications for your engine, feel free to reach out!

🔧 Explore our Outboard Engine Collection of Service Manuals:

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