How to Fix Low Compression on a Jet Ski

Today, we’re diving into a topic that many jet ski owners can relate to: low compression. If you’ve noticed a decrease in your jet ski’s performance or strange engine behavior, low compression might be the culprit. In this guide, we’ll explore what low compression means for your jetski and, most importantly, how to fix it. 

What Are The Symptoms Of Low Compression?

To understand why low compression is a cause for concern, we first need to grasp the concept of compression itself. Compression is the vital process that allows your jet ski’s engine to produce power. 

During each combustion cycle, the piston compresses the air-fuel mixture within the cylinder, leading to an explosive force that drives the engine’s movement. Ideal compression levels range from around 100 to 150 psi (pounds per square inch) for most jet skis. When the compression dips below this range, troubles start to arise. 

While 100-150 is the standard psi range for most jet skis, you should always confirm that information with your dealer or the jet ski user guide from the manufacturer. 

Low compression can cause many problems, such as difficulty starting the jet ski, reduced horsepower, and an overall sluggish performance. If you’ve experienced any of these symptoms, it’s not a bad idea to check the compression to see if that is indeed the culprit. 

There are some DIY solutions we will discuss below, but if those don’t work you may have to take it into a repair shop to get an expert look.

Will Low Jet Ski Engine Compression Reduce the Top Speed?

Yes, one of the symptoms of a low psi will be the reduction in your top speeds. It can be one of the first signs that you potentially have a compression issue.

How to Determine If Your Jet Ski Has Low Compression?

Before diving into repairs, we need to determine if low compression is indeed the issue at hand. To do this, you’ll need a few tools and equipment, namely a compression tester. Don’t worry,  it’s not as intimidating as it sounds and it can be purchased for under $30 on Amazon. Follow these simple steps for a compression test:

  1. Begin with a cold engine and remove all spark plugs.
  2. Attach the compression tester to the first spark plug hole.
  3. Fully open the throttle and crank the engine a few times.
  4. Note the pressure reading displayed on the gauge.
  5. Repeat the process for each cylinder and record the results.

Once you have the compression readings, compare them to the manufacturer’s specifications for your particular jet ski model. If any cylinder falls significantly below the recommended range, you’ve identified low compression.

How to Fix Low Compression on a Jet Ski?

There are different ways to fix low compression on a jet ski, including replacing the worn piston rings, adjust or replace valves, or replace the cylinder head.

Your course of action will depend on what is causing the low compression in the first place. 

What causes lack of compression?

Now that we’ve confirmed low compression, let’s explore the potential culprits behind this issue:

Worn Piston Rings:

Over time, piston rings can wear out, allowing compression to escape past them. To address this, you’ll need to replace the worn piston rings. Here’s a brief rundown of the process:

  1. Remove the cylinder head and the piston.
  2. Replace the piston rings with new ones, ensuring proper positioning and alignment.
  3. Reassemble the engine components carefully, following the manufacturer’s guidelines.

Damaged Valves: 

Bent or burnt valves can compromise compression levels. Depending on the severity of the damage, you may need to:

  1. Inspect the valves and determine if they need cleaning, adjustment, or replacement.
  2. Reseat the valves by lapping them against their respective seats using grinding compound.
  3. If necessary, replace the damaged valves and ensure they’re properly seated.

Cylinder Head Issues: 

Problems with the cylinder head gasket or its mating surfaces can lead to low compression.

To resolve this, you can:

  1.  Inspect the cylinder head for any visible damage or warping.
  2.  Replace the head gasket, ensuring a proper seal between the cylinder head and block.
  3. Torque the cylinder head bolts to the manufacturer’s specifications, following a specific tightening sequence.

By addressing the above causes, you’ll be well on your way to restoring your jet ski’s compression levels. Remember to refer to manufacturer guidelines and service manuals for detailed instructions tailored to your jet ski’s make and model.

Additional Steps to Improve Jet Ski Compression

While fixing the root causes of low compression is crucial, there are additional steps you can take to maintain optimal compression levels.

Regular Maintenance: Follow the manufacturer’s recommended maintenance schedule, including oil changes, air filter replacements, and spark plug inspections.

Fuel Additives: Consider using fuel additives specifically designed to clean carbon deposits and improve engine performance. These additives can provide temporary relief for minor compression issues. If you want to know more about all of the benefits of additives, and my favorite ones to use, I have written an in-depth article here on my favorite fuel additives.

Proper Storage: When storing your jet ski for an extended period, follow proper winterization procedures. This includes draining the fuel system and adding a fuel stabilizer to prevent ethanol-related issues.

Professional Help and Considerations

While DIY fixes are possible, some cases of low compression may require professional assistance. If you’re unsure about tackling the repairs yourself or lack the necessary tools and expertise, it’s always wise to consult a qualified jet ski mechanic. They can diagnose the issue accurately and ensure the proper repair procedures are followed. Keep in mind that seeking professional help may incur additional costs, but it’s a worthwhile investment to ensure your jet ski’s longevity.

We hope this article has helped teach you how to tackle low compression on your jet ski like a pro. Remember, low compression is a common issue, but with the right knowledge and approach, it’s a problem that can be fixed. By understanding the underlying causes, performing proper diagnostics, and addressing them promptly, you’ll have your jet ski roaring back to life. 

As always, if you have any questions or need further assistance, feel free to leave a comment below.
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