How to Replace the Spark Plugs on Your Jet Ski (Sea-Doo, WaveRunner, Kawasaki)

Spark plugs are small, cheap, and easy to ignore. They're also one of the most reliable ways to restore lost performance, improve fuel economy, and ensure your ski starts reliably every time. A set of fresh plugs on a high-hour ski can feel like a minor tune-up — crisper throttle response, easier cold starts, and a smoother idle. This job takes 20–30 minutes and requires almost no mechanical skill.

How Often Should You Replace Jet Ski Spark Plugs?

Most PWC manufacturers recommend replacing spark plugs every 100 hours or every two seasons — whichever comes first. In practice, many experienced PWC owners replace them annually as part of their spring or fall service regardless of hours. Plugs are inexpensive and the peace of mind is worth it.

Replace them immediately if you notice any of these symptoms:

• Hard starting, especially when cold
• Rough idle or misfiring
• Hesitation or stumbling under acceleration
• Reduced fuel economy
• A "CHECK ENGINE" or misfire-related fault code

What Spark Plugs Does Your Jet Ski Take?

Using the correct plug is important. The wrong heat range can cause fouling (too cold) or pre-ignition and engine damage (too hot). Always confirm the plug number in your owner's manual or service manual. Here are the most common specifications:

Sea-Doo (BRP 4-TEC)

• Most 130–230 hp 4-TEC models: NGK DCPR8E or equivalent
• RXP-X 300 / RXT-X 300 (supercharged): NGK DCPR9E (one heat range colder for the higher boost pressures)
• Sea-Doo Spark (60/90 hp Rotax 900 ACE): NGK CR8EB or equivalent

Sea-Doos typically have 3 spark plugs on the 3-cylinder 1.5L 4-TEC engine, accessible from the top of the engine.

Yamaha WaveRunner

• VX / EX Series (TR-1 1.0L 3-cylinder): NGK CR9EIA-9 or equivalent iridium plug
• FX HO / FX SVHO (1.8L 4-cylinder): NGK LMAR8A-9 or equivalent
• GP1800R SVHO: Same as FX SVHO — confirm in your manual

Yamaha TR-1 engines have 3 plugs; the 1.8L F-series has 4 plugs.

Kawasaki Jet Ski

• Ultra 310 series (1498cc 4-cylinder supercharged): NGK LMAR8A-9 or equivalent
• Ultra 160 / STX-15F (4-cylinder): NGK CR9EIA-9 or equivalent

Most Kawasaki Ultra models have 4 spark plugs.

Always verify the correct plug number in your owner's manual before purchasing. Aftermarket iridium and platinum plugs are fine to use and often last longer than standard copper plugs.

What You'll Need

• New spark plugs (correct part number for your model)
• Spark plug socket (usually 5/8" or 16mm) with a rubber insert to grip the plug
• Ratchet and extension
• Torque wrench
• Anti-seize compound (optional but recommended on aluminum heads)
• Dielectric grease (for plug boot connections)
• Shop towels and a can of compressed air

Step-by-Step: Replacing Jet Ski Spark Plugs

Step 1: Let the Engine Cool

Never remove spark plugs from a hot engine. The aluminum cylinder head expands when hot, and removing plugs while hot can strip the threads — a repair that's far more expensive than any plug job. Let the engine cool completely, or at minimum 30 minutes after running.

Step 2: Access the Spark Plugs

Open the engine bay. On most PWCs, the spark plugs are at the top of the engine and are covered by the ignition coils or plug wire boots. The exact access varies by model:

• Sea-Doo 4-TEC: Plugs are under the ignition coil packs. Each coil is held by one bolt — remove it and the coil pulls straight off the plug.
• Yamaha TR-1: Similar individual coil-on-plug design. One bolt per coil.
• Yamaha 1.8L / Kawasaki Ultra: May use coil packs with plug wire leads. Disconnect the wire boot from the plug by pulling firmly straight up — do not yank on the wire itself.

Before removing the plugs, use compressed air to blow out any debris from around the plug holes. This prevents dirt from falling into the cylinder when the plug is removed.

Step 3: Remove the Old Plugs

Thread the spark plug socket onto your ratchet with an extension. Seat it fully over the plug — the rubber insert inside the socket grips the plug so it doesn't fall into the engine bay. Turn counter-clockwise to loosen.

If a plug is very tight or seems seized, do not force it. Apply a small amount of penetrating oil around the plug base and let it sit for 15–20 minutes before trying again. A stripped spark plug thread in an aluminum head is a serious repair.

Step 4: Read the Old Plugs

Before tossing the old plugs, look at them. The color and condition of the electrode tells you a lot about how your engine is running:

• Light tan or gray, worn electrode: Normal wear. Engine is running well, plugs just needed replacing.
• Black, sooty, or wet with fuel: Rich running or fouling. Could indicate a fuel delivery issue, a stuck injector, or a plug that's too cold for the application.
• White or chalky, possibly blistered: Running lean or overheating. Investigate the cause before riding — a lean condition can damage pistons quickly.
• Oily deposits: Oil is getting into the combustion chamber. Could indicate worn piston rings or valve seals. Worth a compression test.
• Broken electrode or cracked insulator: Something is mechanically wrong. Don't just replace the plug — find out why.

If all plugs look the same (normal wear), just replace them and move on. If one plug looks dramatically different from the others, that cylinder warrants further investigation.

Step 5: Prepare and Install the New Plugs

Check the gap on each new plug before installation. Most modern NGK plugs come pre-gapped from the factory, but it's worth confirming. The correct gap for most PWC plugs is between 0.028" and 0.032" (0.7–0.8mm) — confirm the spec in your service manual.

Optional: apply a very thin coat of anti-seize to the plug threads. This makes future removal easier, especially in aluminum heads. If you use anti-seize, reduce the torque spec by about 10% since it reduces friction on the threads.

Thread each plug in by hand first to avoid cross-threading. Then torque with your plug socket and torque wrench:

• Most 14mm PWC spark plugs: 13–18 ft-lb
• With anti-seize: reduce by approximately 10%
• Always confirm the spec in your service manual

Do not overtighten. A cracked plug insulator or stripped thread is the result of too much torque, not too little.

Step 6: Reinstall the Ignition Coils or Plug Wires

Apply a thin film of dielectric grease to the inside of each coil boot or plug wire boot before reinstalling. Dielectric grease prevents moisture from tracking into the connection, keeps the boot from bonding to the plug insulator over time, and makes future removal easier. It does not conduct electricity — it goes on the inside of the boot, not on the electrode.

Press each coil or boot firmly onto the plug until you feel it click or seat. Reinstall the coil bolts and torque them snugly — typically 7–10 ft-lb.

Step 7: Start and Test

Connect your flush adapter, start the engine, and let it idle for a minute. It should start easily and idle smoothly. If it misfires or runs rough, shut off immediately and recheck your connections — a coil may not be fully seated on a plug.

Iridium vs. Copper Plugs: Which Should You Use?

Most OEM specs call for copper plugs, but iridium plugs are a worthwhile upgrade if you plan to keep the ski for multiple seasons. Iridium plugs last significantly longer than copper (often 2x the service life), fire more consistently in demanding conditions, and improve cold-start performance. The price difference per plug is $5–$10 — on a 3-cylinder engine, that's $15–30 extra for plugs that may last twice as long.

Stick with OEM-specified brands (NGK, Denso) and the correct heat range. "Performance" plugs with exotic electrode designs are not necessary and in some cases can cause issues on stock engines.

Bottom Line

Spark plug replacement is one of the easiest and most impactful maintenance jobs on any jet ski. Fresh plugs mean reliable starts, crisp throttle response, and an engine running at its best. Budget 30 minutes, get the correct plug for your model, and do it every two seasons minimum. Your ski will run better for it, and you'll have one less thing to troubleshoot when something goes wrong.

Need help finding the right spark plugs or other service parts for your model? Browse our maintenance parts section or contact us and we'll point you in the right direction.