Here is What the Choke Does on a Jet Ski

Anyone who has cold started a jet ski has the choke on their engine to thank. As is the case with smaller, two-stroke engines, the engine on a jet ski utilizes what is known as a choke to regulate the flow of fuel and air into the engine. This is especially important when the engine is cold, and the fuel tends to form condensate on the walls of the carburetor.

The choke on a jet ski helps to regulate the amount of air entering into the carburetor, thus adjusting the fuel intake to help get the engine started.

While the engines on cars have long since replaced the choke with an electronic fuel injector that monitors the temperature and adjusts the air and fuel intake accordingly, smaller engines like the one on your jet ski still use a manual choke to regulate this process. Not all jet skis are 2-stroke, so this article may not apply to your particular ski.

How Does a Choke on an Engine Work?

In plain terms, the choke is a plate in an engine’s carburetor that regulates the inflow of air. An open choke will allow more air in, which in turn will pull in less fuel, while a closed choke will letin less air, thus pulling in more fuel.

The way this works is dictated by the temperature of the engine that is being started. When the engine is cold, the fuel entering the carburetor is more likely to condensate on its walls, thus being less likely to mix with air and become usable for the cylinder.

For someone starting a cold engine, you’ll want to close the choke. This will cut off the air flow into the carburetor, which will then create a vacuum that will draw more fuel. With a higher amount of fuel in the carburetor, its more likely enough fuel will mis with air and enter the cylinder, in turn igniting the piston.

On a hot engine, or once the engine is up and running, you’ll want to open the choke to allow for more air inflow. This is because fuel condensation will be less of a problem, and it will take less fuel to mix with the air to be enough to enter the cylinder. Keeping the choke closed once the engine is up and running can lead to poor fuel efficiency or completely stalling the engine.

For a full explanation with an illustration, this video does an excellent job of laying out the basics of a choke.

What Does the Choke on a Jet Ski Do?

The choke on your jet ski helps to regulate the air intake on your carburetor, which then helps to start the engine from a cold start.

Most older jet skis run on a smaller engine type known as a two-stroke. Simply put, a two-stroke engine operates on two types of strokes from its pistons: a power stroke and an exchange stroke. Being smaller and a bit limited in their output, two-strokes are common on jet skis and other smaller machines like lawnmowers and chainsaws.

Due to their smaller nature, two-strokes often feature a manual clutch that can be adjusted by the operator to align with the conditions under which the engine is being started. A cold start will require a closed choke that allows for more fuel intake. A running motor or hot spring will need an open choke to help allow for more air intake into the carburetor.

The ability to manually regulate this means the operator has the control in terms of getting the engine going.

For a more thorough explanation of how two-stroke engines and their chokes work, check out this article from Engine Basics. Save 15% OFF on High Quality Marine Repair Manuals

What are some common problems with the choke on a jet ski?

Problems with the choke on your jet ski can be problematic for both starting your jet ski and keeping it running correctly. These problems will generally manifest themselves in the cold start process, and are usually an easy fix.• 

Faulty/Misadjusted Choke

Being the main component aiding in the cold starting process, a faulty choke will make it difficult, if not impossible, to start your jet ski on a cold start. This is usually caused by the fact that the choke itself can be a relatively sensitive piece of equipment that can be thrown off without much force.

A faulty choke will prevent the proper combination of air and fuel from entering the carburetor, thus preventing the engine from turning over in the case of a cold start. This can be caused by a broken bimetal spring that helps to open and close the choke. If the spring is broken, the choke won’t close, and will therefore never create the fuel-rich mix that is needed to start a cold engine.

A faulty choke can be a fairly easy fix. A choke repair kit or a new bimetal spring is a fairly affordable component, and neither repairing the choke nor replacing the bimetal spring require you to replace the entire carburetor, a far more expensive repair.

 Dirty Choke Shaft

Another common cause of issues with an engine’s choke is simply dirt and grime buildup on the choke shaft. Over time, as grease and sediment collect in the shaft they can cause sticking that hinders the choke’s ability to open and close. If left unchecked, it can give the impression of a broken choke, similarly making it difficult for the engine to turnover on a cold start.

This is another easy fix, as the choke shaft can be accessed relatively easily. Once accessed, clean any buildup with a basic cleaning agent and a brush.

Faulty Choke Cable

The choke cable is the component that connects the choke in the engine to the choke adjuster that the jet ski operator uses. If this cable is broken or not working correctly, the operator may not be able to adjust the choke to accommodate what the conditions require.

This is another easy fix, as replacing a choke cable is a simple process. While the cable itself will run you about $90, the process of connecting it to the choke and the manual adjuster near the ignition is a fairly straightforward one.

All of the above issues will present themselves in the same way. Your jet ski will have trouble cold starting and will struggle to hold an idle without stalling once running. Because all of these problems manifest themselves in the same way, you’ll want to go through each of these common possibilities to make sure you’re addressing the correct problem.

Choke vs. Primer?

Many jet ski owners will report using a combination of the throttle and the choke to get their jet ski to start cold. While most owner’s manuals will only call for the adjustment of the choke, many operators report a combination of adjusting both to be a good combination for getting their jet ski to start.

Those who are familiar with starting other two-stroke engines, such as chainsaws and weed-whackers, will be familiar with this sort of freestyle startup. While you’ll almost always start the process with the choke closed, knowing when you’ll adjust it and by how much will mainly be a process of feeling out your engine.

For many, it’s a matter of listening to what the engine is doing. Once you’ve primed the engine a little and attempted to turn it over a couple times, you’ll often hear the engine begin to start before sputtering and stalling. This is generally the point at which most operators open the choke up a bit and try again. At this point your engine will likely start up.  Then you’ll want to open the choke fully to prevent stalling.

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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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