Why is my Jet Ski Backfiring and what it means?


Most people have heard the backfire of a car, or older motorcycle, but hearing it on your jet ski can also be a shocker. There are many causes to a backfiring wave runner, so lets to over them and how to troubleshoot.

With each jet ski being specific, there is not one single post that can give you each detail about timing, and what to check, but I hope this general guide gives you ideas of what to check next time you have a wave runner or jet ski that won’t stop backfiring.

Why is my jet ski backfiring? Typically a jet ski will backfire due to a timing problem which is causing fuel to be burned at a different time than it is supposed to such as when the exhaust valves are open. It can also be caused by many other items such as switched plug wires, or bad reeds.

Causes of a Jet Ski Backfire:

There are many causes to why a jet ski would backfire, this ranges from easy simple solutions to hard to diagnose problems. Lets go over the main reasons your wave runner would backfire.

Switched Plug Wires

One of the first things to check on your wave runner if you have a backfiring problem is if the plug wires are switched.

Let’s say you winterized your ski and pulled your plugs out, well, when you put them back in the wires need to go back to the same locations. Next spring you get your ski out and boom backfire.

This is one easy item to troubleshoot, so this is our first thing to look for. If you have not missed with the plug wires in some time and the jet ski has ran fine, then move down the list of other potential problems.

Timing Problem

A timing problem is another cause of backfire on a jet ski. If your jet ski ignites fuel when it is at a different point in the ignition process, then it will either backfire through the exhaust or through the carbs. Having a good flame arrestor such as your stock or upgraded model is key to prevent other damage such as fire due to a backfire through the carb.

A timing backfire can be found by checking the timing as you would on an automobile with a timing light. You can also check your shop manual to find out which piston for our specific wave runner needs to be set to TDC (top dead center) with a feeler gauge (pencil or stick if need be) and look at the markings on the flywheel. These would need to be set to stock per the factory shop manual.

Broken Reed

A broken reed can be another cause of a backfire problem. The cracked, chipped, or stuck reed can be letting air in causing a backfire. To find out if you have a broken reed, remove your reeds and inspect to see if there is anything wrong with your reeds such as a chip, crack, or anything sticking.

Out of phase crank

An out of phase crank can also be the culprit of a backfire problem. This could be if you recently did a rebuild on a motor or if it suddenly stopped on the lake. This would need to be diagnosed by inspecting the crank to the timing. This is an unlikely cause, but could happen.

Sheared Woodruff Key

A sheared woodruff key is something that can cause your timing to become out of wack and cause a backfire. A sheared woodruff key can cause the flywheel to spin freely not with the crank of the engine. This will cause the engine to be out of sync and cause the valves to be opening at the wrong time. Your jet ski would then backfire through the exhaust or the carbs due to mis ignited fuel.

Sea-Doo Specific Items

If you have a Sea-Doo, you will possibly have a rotary valve. The following troubleshooting ideas are specific to Sea-Doo’s.

Rotary Valve out of Timing

Your rotary valve may be out of timing just as your engine can. You will need to follow your shop manual to check your timing and verify that it is correct on both of your rotary valves.

Bad Brass Gears in the Rotary Valve

The brass gears that turn the rotary valve can go bad with sheared off splines. This will cause the valve to skip and become out of time. You will need to visually inspect your gears to ensure they are good, it is suggested to do this the same time as you check your rotary valves for timing.

What is a backfire?

A backfire is when the fuel ignites at the wrong time. Typically this can either come out of the carb or out of the exhaust. This is due to the ignition of fuel can happen out of time on the exhaust or intake side of the engines process. Most cases you will hear a boom, in some it may sound like a gunshot, and in other cases, you may blow up your water box and need to invest in hearing aids.

Lets hope the latter does not happen as that would cause another item to troubleshoot.

Final Thoughts

Hopefully one of these solutions has let you find your issue and fix your problem so you have a good ski to ride. If it does not, you can also take it to your friendly mechanic and they can diagnose the problem and fix it for you.

Happy Riding!

Eric

I have been an avid boater / jet ski fanatic since I was a kid.

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