Compression is defined as the pressure a given fluid exerts when confined in a fixed volume. To determine what compression should be on a jet ski, you must first understand how it works. The jet ski engine fires up and spins two wheels called impellers around very fast, mainly using cylinders charged with air or fuel mixture.
Compression of 135 PSI or greater, considered optimal, should be on a jet ski. Compression of 85 PSI or lower, however, is considered awful. The ideal scenario is for all cylinders to give the same or comparable reading. Furthermore, that reading should be at least 135 PSI.
Keep reading as we explore what compression should be on a jet ski, the various factors that affect it, and ways of achieving maximum performance with minimum hassle. The process is quite simple if you know what you’re doing.
Why Should Compression Be 135 PSI on a Jet Ski?
Compression serves two main purposes; boost horsepower and create high octane fuel for combustion. Having a 135 PSI compression level ensures your jet ski performs appropriately.
Higher compression leads to smaller air spaces between the piston rings inside the engine cylinder. It creates intense heat, which eventually leads to a loss of power well past the optimal compression level. That’s why you’ll find most high-performance engines running at lower compression levels than their non-high performance equivalents.
How To Test Compression Yourself
Compression should always be well within range for your engine to run well. You should do the compression test on a flat surface. Although it’s best done with the engine running, you can get an accurate reading by putting your jet ski in neutral and cranking it over until there’s no resistance anymore.
To test compression on your jet ski, follow the steps below:
- Turn on the engine and allow it to warm up for several minutes. That’s where you may want to put the kill switch in so it doesn’t kick off if you forget about it while checking other things, like oil levels or coolant.
- Listen for abnormal noises. With the engine running, listen closely for any knocking or pinging noises that aren’t normal operation sounds coming from inside the motor box area of the hull.
- Locate the spark plugs. They’re usually at a wire’s end. If you’re unable to locate them, the owner’s manual will have that information for you. An engine cover likely covers the spark plugs, so you may need to remove the cover to get to the spark plugs.
- Remove each spark plug one at a time. Do this using your hand or a socket wrench, depending on how difficult it is to remove it.
- Use a compression gauge. With the spark plug removed, take your compression gauge and insert the needle end into the cylinder head valve hole where the spark plug was located previously.
- Read the gauge. Be sure that it matches up with what you know should be there according to specifications found in your owner’s manual or online if available for free at other sites without having to pay for access.
- Repeat this step for all cylinders that are working properly. Do this before proceeding to test cylinders that aren’t working.
Factors That Affect Compression
When looking for what should be the correct compression on a jet ski, you need to know all the factors that affect it so that you can achieve maximum ease of use with minimum headache. The significant factors that affect compression are as follows:
- Fuel quality
- Ignition timing
- Air filters
- Intake manifolds
Generally speaking, however, most watercraft engines should run at closer to normal compression levels than their equivalents on land would. As long as you don’t push them past 135 PSI (which is reaching peak), you’ll be fine.
How To Get the Best Out of Your Jet Ski
Achieving peak performance from your jet ski depends on several other factors apart from knowing the correct compression on a jet ski. Some ways to enhance performance include:
Consider Water Level and Buoyancy
The water level in a jet ski doesn’t affect the compression ratio. However, it’ll lower performance by reducing buoyancy and therefore speed. If your water is too low, you should refill it before trying to diagnose other problems with your engines’ function.
Jet skis are designed to be equipped with sufficient buoyancy so that they don’t sink when swamped or tipped over while remaining stable enough for riders to remain safely on top during high seas and rough waters.
Manufacturers deliberately add ballast weight inside the hull below the waterline to achieve this effect. This has no bearing whatsoever on how well or badly a jet ski runs, although it can affect its stability somewhat if it’s overloaded.
Choose Good Fuel Quality
Two-cycle engines naturally have lower compression ratios than four-cycle engines. They don’t directly link air and fuel to the combustion chamber through a valve-controlled opening of the intake port during each stroke.
Instead, four-cycle engines utilize a higher compression ratio for better fuel efficiency by drawing in extra air molecules with power provided by an electric motor and followed by introducing them into the engine cylinder at the time of ignition, requiring much more force than usual.
Moreover, four-cycle engines can be tuned to increase the amount of compression that occurs before ignition. This allows for greater performance over two-stroke equivalents that rely on more easily combustible fuels such as gas or oil mixed with their fuel instead.
The quality of fuel you use has a great deal to do with how much compression is generated. Fuels such as alcohol and diesel can boost the compression ratio well over 10:1, which translates into higher speeds and more power than gasoline alone.
However, 95% ethanol (the kind found in grocery stores) cannot be used for this purpose because it fuels engines poorly, creating excessive engine wear due to its incompatibility with modern fuel injectors.
Compression is an important factor when it comes to jet ski engines. The compression reading should be at least 135 PSI for all cylinders to have optimal engine performance.
If your jet ski has a compression of 85 PSI or lower, you might need to get that checked out by a mechanic right away before there are any significant problems with your engine. A low-compression issue can lead to many other issues down the line so stay on top of this.