11 Reasons Your Jet Ski Isn’t Reaching Full Speed

Are you experiencing issues with your jet ski? Is it failing to perform as expected or making unusual noises? Regardless, when a personal watercraft doesn’t perform at its peak, it can be incredibly frustrating, and I want to provide some guidance.

There are many reasons why you’re not reaching top speed on your jet ski.

Let me highlight some common causes and share practical solutions to help you get back on the water at full power.

Key Points:

When it comes to top speed, here are the more common reasons why your jet ski is suffering.

1. You’ve sucked something up.
2. Damaged jet pump.
3. Supercharger failure or loose hose.
4. Wrong key.
5. Wrong driving mode.
6. Still in break-in mode.
7. Not trimmed right.
8. The Speedometer lies.
9. Bad gas.
10. Bad spark plugs.
11. Blown engine.

This list is geared more towards 4-stroke jet skis, if you have a 2-stroke some of this will still apply to you, and if none of the above work, then it’s probably your carburetor, and it needs to be cleaned or replaced.

Let’s go over each point and show you want you can do about it!

1. You’ve Sucked Something UP

One of the most frequent issues with personal watercraft is accidentally sucking up debris.

Rocks, sticks, sand, and similar objects can enter the pump and lead to a range of performance problems.

If you’re noticing reduced performance or unusual operation, inspect the pump thoroughly to ensure that no debris is causing blockages or interfering with proper functionality.

2. Damaged Jet Pump

Sucking up debris often results in damage to components like the wear ring or impeller, which are part of the jet pump.

However, damage to the jet pump isn’t always caused by debris.

Another potential issue could be a damaged through-hull seal, which can disrupt the performance of your personal watercraft.

To identify any problems, inspect the jet pump for visible damage. A thorough inspection may require removing the pump, as some issues aren’t visible externally. Keep in mind that certain parts of the jet pump might need specialized tools, so a repair shop could be your best option. That said, you can still check the intake and rear area for anything unusual.

3. Supercharger Failure Or Loose Hose

If your watercraft is equipped with a supercharged engine—common in models with over 200 horsepower—a failing supercharger can significantly affect performance.

For instance, a machine that once reached speeds of 70 MPH may now only manage 60 MPH. This reduction in speed is often a clear sign of supercharger failure, which needs to be addressed to restore full functionality.

Hose Blow Off

One thing to look out for is the supercharger hoses have not blown off. I’ve seen this quite a bit, as the superchargers put out a lot of pressure. Look around the rear of the engine for the supercharger hoses and make sure they’re not loose.

Check RPMs

If you have a supercharged engine, you need to check it for boost, but most often if you have a supercharged engine, and it’s not going above 7,000 RPMs then it’s most likely your supercharger.

4. Wrong Key

Sea-Doo, Yamaha and Kawasaki all have key options that control the power of the jet ski.

For example, Sea-Doo has a learning key that limits from 32 MPH up to 50 MPH, depending on the model and how it was programmed.

Yamaha has key fobs and Kawasaki has similar keys to Sea-Doo, they all can limit the power.

Avoid Mixing Up Your Keys

It’s quite common for people to forget that these keys exist and grab them because they lost their normal key. So make sure you don’t have a slow key or the fob set to the lower output.

Rental Key

There is even a rental key that limits them to 45 MPH. If you bought a rental jet ski, make sure they made the key fast and removed any other limiters that their insurance company makes them have.

5. Wrong Driving Mode

Just like the keys, most jet ski have different driving modes.

You have

• Touring.
• Sport.
• ECO.
• And many others with similar names.

What is interesting is that these driving modes are more about slower take-off than affecting top end. But some modes like ECO will limit from 40MPH to 50MPH.

Make sure you’re not in a different mode that is limiting your top end, it will clearly state the mode on the display.

6. Still In Break-In Mode

It’s becoming more common for new models of all sizes to have a break-in mode. Even the lower horsepower models still have high-performance engines, and proper break-in is important.

Not many people do engine break-in properly, so the manufacturers are now doing forced break-ins. This means the engine is not fully unlocked, and you will not get to max power for a bit.

5 Hours

Usually, after the first 5 hours the engine will unlock itself, but it can go up to 25 hours to fully be broken-in or could happen after the first service. The more HP your engine has, the more the break-in is forced.

7. Not Trimmed Right

If your jet ski has trim, sometimes called VTS on Sea-Doo, make sure you have the trim set correctly.

If you’re drag racing, you want the trim all the way down, then when you get on plane, raise it up.

Don’t trim all the way up, or it will want to jump out of the water.

Every machine is different, you will need to find the sweet spot for your trim, the wrong trim height will affect output.

8. The Speedometer Lies!

If you’re sweating over a few MPHs, then the honest truth is that the speedometer can lie.

The speedometer on a lot of jet skis is not accurate at all.

Some do use GPS to get their MPH, but even that can be fudged a bit or get off due to cloud cover.

RPMs Matter More

It’s the RPMs that matter, not the MPH. It’s when the RPMs are not what they used to be that you need to worry.

I’ve even had people mix up KPH with MPH. One person insisted his GTI previously reached 100 MPH, but now it only achieves 60 MPH. It turned out that it was initially set to KPH, and 100 KPH is approximately 60 MPH.

9. Bad Gas

Gas isn’t what it used to be ever since they started adding ethanol, and it’s been super annoying for boats.

If you did not put stabilizer in your gas when storing your boat for months, there is a good chance the gas has gone bad. Bad gas can lead to all kinds of problems, especially with supercharged engines.

If the gas tank is under a half a tank, put some premium gas in and see how it responds. Add marine fuel stabilizer (Amazon Link Ad) to the gas to help with any water that may have gotten in the gas.

10. Bad Spark Plugs

You should change the spark plugs in your jet ski every 50 hours, or once a year.

Bad spark plugs can cause all kinds of issues, and with how easy they are to change, it’s a no-brainer to do it every year.

11. Blown Engine

In extreme cases, a personal watercraft failing to perform at its peak may be caused by a blown engine.

To determine if this is the issue, check the compression, bearings, and give the engine a thorough inspection to rule out significant damage.

Engines that have been neglected—or even well-maintained ones—can fail, leading to drastically reduced performance or complete inoperability.

While a blown engine is often a last-resort diagnosis, it’s worth considering if other troubleshooting steps haven’t resolved the problem.