How to Change Spark Plugs on a Jet Ski

It might be intimidating to work on your own jet ski, but on many models of jet ski have spark plugs that are both easy to access and replace. Spark plugs also need to be replaced relatively often on jet skis in comparison to other motorized vehicles. 

How do you change spark plugs on a jet ski? This guide will tell you the following:

  • How often spark plugs in a jet ski should be changed
  • What symptoms your jet ski might exhibit if it needs a spark plug change
  • The basic procedure for changing out jet ski spark plugs

Replacing spark plugs on a jet ski might seem confusing at first, but it isn’t really difficult. Read on to find out more about changing out the spark plugs on your jet ski. 

I do want to get one important tip in here before you read on: when working on your PWC, try very hard to not drop anything. It can be very hard to fish out parts, tools, debris or anything else that gets dropped into the hull. Keep a spring clamp and magnet retrieval tool handy at all times. Now that’s out of the way, read on.

What Are Jet Ski Spark Plugs? 

Just like in a car or other motorized vehicle, a jet ski has spark plugs that form part of the ignition system in the jet ski’s motor. In a fuel-based motor system, these plugs are what allows the engine to ignite fuel for the thousands of mini-explosions that drive your vehicle or watercraft. Engines need 3 things to run: fuel, air, and something to ignite those. 

The spark plugs are the third part of the equation. Fuel and air, of course, are always being replenished.  But spark plugs need to be replaced at regular intervals to maintian peak engine performance as well as best fuel economy.

Once a spark plug is fouled, it cannot supply enough voltage to the ignition cylinder of the engine to spark it. This leads the engine to misfire or not fire on all cylinders. This causes a noticeable loss of performance in the jet ski. 

In a car’s motor, spark plugs are most often damaged by oil leaks. In jet skis, spark plugs are commonly fouled by the following causes:

  • Too much idling: An engine does not perform at peak temperature when it’s at idle, and this can lead to a build-up of debris in the engine’s spark plugs and fuel injectors
  • Too much fuel: An overly rich fuel mixture or overfilling the gas tank can lead to spark plug fouling
  • Too much oil: Overfilling with oil can cause oil to spill over and foul the spark plugs; oil leaks in the jet ski’s engine can also cause spark plug fouls. Too much oil can cause many problems and needs to be avoided.
  • Time: Spark plugs gradually worsen over time just like any electrical or mechanical part.

All of these situations can easily lead to a jet ski’s spark plug becoming fouled under the right circumstances, and it only takes one fouled spark plug out of the set to cause significant running problems, even if the jet ski’s motor does continue to start and run. 

Spark plugs are easy to replace with just a little bit of background knowledge on the jet ski you’re operating. Most jet skis come with operator’s manuals that contain concise explanations on how to find the spark plugs on your jet ski and remove them. 

It’s always best to look at the instructions for your specific model in order to get the best results from any maintenance or repair. The design on most jet skis is simple enough that the operator/owner is capable of performing minor repairs like spark plug replacement without involving a watercraft technician. 

When your jet ski starts acting up, it’s easy to want to throw the problem at a mechanic right off the bat, but performing just a little minor troubleshooting can save you hundreds of dollars in labor in the long run.  

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When Should You Change Your Jet Ski Spark Plugs?

Spark plugs for jet skis are relatively cheap because they require replacement often, but how often depends largely on how often the jet ski is used. Depending on whether a jet ski is ran continuously or only ran a few times a season, the plugs may have to be replaced multiple times in a year. Here are a few guidelines for how often to change your jet ski spark plugs:

  • If you use your jet ski often, you will probably need to change out the spark plugs approximately every fourth or fifth time you take it out, or every 25 hours of engine time.
  • If you only use your jet ski occasionally (a few times a month), you can replace the spark plugs less often, but again check engine hours and your manual. 
  • Spark plugs should be replaced whenever winterizing a jet ski or putting it up in storage for the winter annually. 

On top of these maintenance replacements, spark plugs should obviously be replaced any time the jet ski begins to suffer in performance. Since they are so cheap, it’s a good idea to keep an extra set of spark plugs set aside in the maintenance area for your watercraft so that you can find them easily whenever they need maintenance. 

If the spark plugs are replaced, and the jet ski’s performance doesn’t improve, you’ll have already eliminated one of the possible simple causes and can move on to involving a professional to take a look at the engine. 

How often you need to replace the spark plugs will also be dependent on how you drive the jet ski. If you are riding the jet ski continuously at low speeds (such as the speeds found in “no wake” zones), then you’re going to be fouling a lot of spark plugs. If you do faster running on your jet ski, however, you will not need to replace them as much.  

How Jet Skis Act When the Spark Plugs Need Replacement 

Spark plug issues are one of the most common and simplest problems that people run into when running a jet ski, and these problems are obvious enough that you don’t need mechanical experience in order to notice them. 

The symptoms that lead to a jet ski needing spark plug replacement can generally be categorized under “running problems.” Here’s how a jet ski will act when the spark plugs likely need replacement:

  • The jet ski will ride rough or feel like it has a stronger vibration than usual
  • The jet ski may sound louder or have a rattling noise while idling
  • The jet ski may suffer from a loss of power during acceleration on the water
  • The jet ski may be difficult to get running (this will become worse as the spark plugs become more defective and eventually kill ignition altogether)

One of the good things about weak or defective spark plugs is that they usually begin to cause symptoms with the jet ski’s performance before the jet ski dies entirely, so you have a little bit of time to address the issue before getting the jet ski down to the local marina’s repair bay becomes a major hassle. 

How to Change Spark Plugs on a Jet Ski

While some aspects of spark plug location might vary from jet ski model to jet ski model, the same basic procedures for removing fouled spark plugs and replacing them can be performed across all models of jet ski. 

Follow this procedure to change the spark plugs on a jet ski:

  • With the jet ski OFF, take the seat off and lean it up against the hull of the jet ski to expose the engine compartment. Make sure that the jet ski’s engine is cool before touching any exposed part of the jet ski’s mechanisms. 
  • Remove the engine or spark plug cover. Your jet ski owner’s manual should show you where this can be located on your jet ski, depending on what model you own
  • Pull the ignition wire from the spark plugs.  I pull all at once and then insert the wire back into the cylinder opening to keep out dirt and to keep from accidentally switching up the connections.
  • Use a small specific spark plug socket and ratchet to remove the spark plugs. That rubberized insert in the spark plug socket is critical to be able to pull the plug out and replace without dropping the new plug. A regular socket will work, but you will be dropping the old and new plugs several times before finishing the job.
  • If you encounter any resistance while trying to remove the spark plugs, try using some PB Blaster, a penetrating anti-seize lubricant that can be purchased at an auto supply shop like O’Reilly’s or AutoZone. 

Note: At this point, if you still cannot get the spark plugs out, take your jet ski to a repair mechanic rather than forcing the spark plugs out with a wrench. This can cause significant (and expensive) damage to the engine block.  

  • Once the spark plugs are loose in the socket, hand turn them the rest of the way to gently free them from their fittings. Be very careful not to drop your ratchet or extensions, as the engine compartment is tight. Whether the wrench gets jammed in the engine compartment or drops through to sink into a lake, you’re not going to be happy. Have a magnet or spring-loaded retrieval tool handy to grab items dropped into the hull.
  • Once the spark plugs are removed, inspect the spark plug fittings. You will see a hole that leads down to the injectors. Make sure this part of the fitting is not wet and make sure it dries thoroughly if it is before adding a new spark plug. To hasten the drying process, dry gas treatment can be used. 
  • Once the spark plug fittings are completely dry, inspect the new spark plugs to see if you need to remove the terminal cap.  Look at the old plug to determine this. You’ll then use a gap tool to make sure the plug is gapped properly. 
  • Add a coating of anti-seize compound to the plug threads before inserting them. Start by placing the new plug in the socket far enough that the rubberized insert holds it in place. Hand-screw the fresh spark plugs down, then tighten them with the ratchet. Don’t overtighten.  Spark plugs don’t need to be overtorqued, and this can actually damage the plugs.
  • Replace the spark plug ignition wires and the engine cover. At this point, the jet ski has all new spark plugs and you’re good to go!

If Changing the Spark Plugs Doesn’t Work

If you’ve changed the spark plugs in your jet ski and it still doesn’t work, you have at least managed to eliminate one potential source of the running problem, which will reduce any further time you have to spend troubleshooting.

If replacing the spark plugs doesn’t fix the problem, you have two choices: continue to troubleshoot the problem yourself or contact a repair mechanic to look the jet ski over. 

Which decision you make will depend on how much mechanical experience you personally have. Those who enjoy working on motorized vehicles for fun and already have the tools to make the attempt would probably be a good candidate for attempting an at home repair.

However, if you don’t have that level of mechanical know-how, it is better to leave the work to professionals rather than cause any kind of lasting damage to the jet ski that might eventually render it inoperable or necessitate costly repairs. 

Jet Ski Tool Kits

Depending on what model of jet ski you buy, you can purchase comprehensive tool kits for the jet ski that help you.

While all jet skis are a lot alike and many tools may be able to carry over from one model to another, it can be helpful to have tools that are designed specifically for your model of jet ski, no matter whether you ride a Waverunner or a Kawasaki. 

It’s also very important for you to have an owner’s manual for your specific model of jet ski in case maintenance or repair issues come up. If you didn’t get an owner’s manual with purchase or it has since been lost, you can get a replacement aftermarket owner’s manual online. 

Many of these manuals and instructions can be found for free online, but if you want a hard copy, these are also usually available depending on which model you own. 

Videos for Replacing Jet Ski Spark Plugs

When learning how to replace spark plugs or perform any kind of mechanical work, it can sometimes be helpful to watch a video of another person changing spark plugs on a jet ski. This is because people learn in a variety of ways. 

Reading this guide on changing spark plugs in jet skis can give you a basic understanding of how the task is accomplished, but it won’t give you as clear an idea of how it is accomplished as being able to watch someone perform the task will.

Some people are also better auditory learners, and these people benefit from having verbal instruction rather than reading instructions in an owner’s manual or guide. 

Here are some other good videos in addition to mine above that show how easy it is to replace spark plugs on a jet ski regardless of which model you own:

These videos (and many others available on YouTube and elsewhere) can go a long way towards teaching you some basic maintenance and repair on your jet ski that you can perform at home in order to avoid putting the jet ski into the shop for repairs. 

Besides saving you some money, learning how to perform these kinds of basic repairs at home can teach you more about how motors work and lead to you ultimately becoming a more self-reliant individual. How about that for some self-empowerment! 

If It’s Not Spark Plugs, What Could It Be?

If you’ve changed out your spark plugs correctly to the best of your ability and it hasn’t positively affected the running performance of your jet ski, you obviously have some kind of other problem going on. There are several engine-related mechanical problems that can lead to a jet ski developing power loss or a hard start issue other than fouled spark plugs. 

Here are some of the other issues you might be dealing with in your jet ski:

  • Clogged fuel lines: Debris in your fuel lines can lead to a clogged carburetor, which in turn can lead to jet skis that are difficult to start 
  • A worn jet pump: The jet pump on the underside of the jet ski can become worn after years of use, and if it’s worn, this will lead to a symptom of heavy vibration similar to the vibrations felt in a jet ski with failing spark plugs. 
  • Bad battery: Often times when a jet ski’s battery is beginning to fail, either due to old age or cold weather conditions, the symptoms caused by a bad battery are similar to those caused by bad spark plugs. To rule it out, put your jet ski’s battery on a battery tester and test the charge to see how it’s holding up. 
  • Failing engine seals: Tight engine seals and gaskets are important for an engine to work properly, and when these seals begin to fail, so does the engine. Gasket repair is usually intensive engine work best left to a mechanic. 

Problems like these typically require tools and know-how beyond a layman’s abilities, so don’t feel bad if you end up calling in a more knowledgeable cavalry charge to help out. Small engine maintenance isn’t for everyone, and you’d rather pay a repair bill than know you’re the cause of even more expensive damage. 

Jet Ski Spark Plugs Can Be Replaced at Home

Regardless of whether replacing the spark plugs in your jet ski fixes any running problems, it might have, spark plugs go bad on jet skis often enough that replacing them as regular maintenance typically falls to the owner rather than a mechanic. 

Since this is the case, learning how to replace the spark plugs on your jet ski is an almost crucial skill involved with keeping one. If you can’t remember the last time your jet ski’s spark plugs were changed, pick up a box of spark plugs, grab your owner’s manual, get started!


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Tim Conner, M.D.

Tim Conner, M.D. started boating in 1974. He has been involved in recreational boating continuously since then. Dr. Conner has been active in boating and watersports safety education for decades. He rode his first jet ski in 1997, and rejoined the personal watercraft arena in 2012 with a Sea-Doo GTX 155, followed by 2 supercharged SeaDoos. Scuba certification came in 1988, and he and the family have traveled the world snorkeling and scuba diving for decades. The family has recently taken up paddle boarding. Click the photo for a lot more.

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