How to Replace the Spark Plug on a 2018–2021 Honda Monkey
Replacing the spark plug is one of the simplest maintenance jobs you can perform on your 2018–2021 Honda Monkey. A fresh spark plug helps ensure reliable starting, smooth running and optimum fuel efficiency. Best of all, it’s a straightforward DIY task that requires only basic tools and around 30 minutes of your time.
| Specification | Value |
|---|---|
| Difficulty | ⭐⭐☆☆☆ Easy |
| Time Required | 20–30 minutes |
| Estimated Cost | £10–£20 |
| Model Covered | 2018–2021 Honda Monkey (JB02) |
| Skill Level | Beginner |
Why Replace the Spark Plug?
The spark plug is responsible for igniting the air and fuel mixture inside the engine.
Over time, the electrode gradually wears and deposits can build up, making the spark less efficient.
Symptoms of a worn spark plug may include:
- Hard starting.
- Rough idle.
- Reduced fuel economy.
- Hesitation when accelerating.
- Occasional misfires.
Fortunately, replacement is inexpensive and can restore smooth performance.
Before You Start
Always work on a completely cold engine.
Removing a spark plug from a hot aluminium cylinder head increases the risk of damaging the threads.
Park the motorcycle on level ground and switch off the ignition.
What You’ll Need
Tools
- Spark plug socket
- Ratchet
- Extension bar
- Torque wrench
- Clean cloth
Parts
- Genuine Honda recommended spark plug (or approved equivalent)
- Small amount of dielectric grease (optional)
Always confirm the correct spark plug specification for your exact model year before purchasing.
Step 1 – Remove the Seat
Unlock and remove the seat following the instructions in your owner’s manual.
This provides easier access to the top of the engine.
Step 2 – Locate the Spark Plug Cap
The spark plug sits at the top of the cylinder head beneath the ignition cap.
Before removing anything, wipe away any dirt around the plug area.
This helps prevent debris falling into the engine.
Step 3 – Remove the Plug Cap
Grip the rubber cap firmly.
Twist gently while pulling upwards.
Avoid pulling on the ignition lead itself.
Step 4 – Remove the Old Spark Plug
Using the spark plug socket and extension, carefully unscrew the old plug.
If excessive resistance is felt, stop and investigate rather than forcing it.
Once removed, inspect the spark plug.
Step 5 – Read the Old Spark Plug
The condition of the old plug can tell you a great deal about how the engine is running.
Generally:
- Light tan or grey deposits indicate normal combustion.
- Dry black deposits may suggest an overly rich mixture or excessive idling.
- Oily deposits could indicate oil entering the combustion chamber.
- White or blistered electrodes may indicate overheating or an incorrect heat range.
If the plug shows unusual wear, it may be worth investigating further before fitting a replacement.
Step 6 – Install the New Spark Plug
Thread the new spark plug into the cylinder head by hand first.
This is important because it helps avoid cross-threading the aluminium cylinder head.
Once finger-tight, use a torque wrench to tighten the plug to the specification given in the Honda workshop manual.
If you don’t have a torque wrench, follow the tightening instructions supplied with the spark plug manufacturer—but using the correct torque is always recommended.
Step 7 – Refit the Plug Cap
Push the ignition cap firmly onto the spark plug until it clicks securely into place.
Ensure it sits squarely on the plug.
Step 8 – Start the Engine
Start the motorcycle.
The engine should idle smoothly and respond cleanly to the throttle.
If it misfires or runs unevenly, switch off the engine and check that the plug cap is fully seated.
Common Mistakes to Avoid
- Removing the plug from a hot engine.
- Pulling on the ignition lead instead of the plug cap.
- Cross-threading the new spark plug.
- Overtightening the spark plug.
- Allowing dirt to fall into the cylinder.
When Should the Spark Plug Be Replaced?
Honda includes spark plug inspection and replacement within the official maintenance schedule.
Even if the bike appears to run normally, replacing the plug at the recommended interval helps maintain optimum performance and reliability.
Always refer to your owner’s manual for the correct replacement interval for your model.
Motorhome Monkey Verdict
Replacing the spark plug on a 2018–2021 Honda Monkey is one of the easiest maintenance tasks you’ll undertake.
With minimal tools and very little expense, you can help ensure reliable starting, smooth running and efficient fuel consumption.
It’s an ideal DIY job for owners beginning to service their own motorcycles and another simple way to keep your Monkey in top condition.
🔧 Motorhome Monkey Top Tip
Before removing the old spark plug, use compressed air or a soft brush to clean around the spark plug well. Preventing grit from falling into the cylinder is just as important as fitting the new plug correctly.
Editorial Note
This guide applies to the 2018–2021 Honda Monkey (JB02). Always confirm the correct replacement spark plug and tightening torque in your Honda owner’s manual or workshop manual, as specifications can vary between model years and markets.
