It’s not uncommon that ATV-owners find themselves with a machine that won’t stay running or won’t run properly. Sometimes the ATV won’t run at idle, or it may bog down when applying throttle. Some find that their ATV starts and runs fine, but only for a short time before it shuts off.
In this post, we will have a look at the most common issues to look into when your ATV keeps turning off.
To make troubleshooting a bit easier, we’ve categorized the various issues most likely to occur, depending on how the bike behaves. Note that the listed issues overlap the various symptoms. You may just as well find the root of your problem under a headline that does not necessarily fit the specific behavior of your machine.
When the ATV will not run at idle
In this first scenario, we will look at what may be causing your problems when the ATV:
- It starts as normal or is slightly hard to start.
- It may run as normal when you ride it, but you may also have a hard time getting the engine to rev up.
- As soon as you let off the throttle, the engine will stop.
- Alternatively, it may run only for a few seconds at idle.
The idle is set too low
Carbureted ATVs have a set screw that adjusts at what RPM the bike should idle. Whenever it is set to low, the carburetor will not provide enough gas to keep the engine running.
This is how you adjust the idle on a carbureted ATV:
The spark plug(s) needs replacing
Inspecting your spark plugs can help diagnose the nature of the problem that is preventing your ATV from idling correctly. Remove the spark plugs and have a good look at them.
- A healthy spark plug should have a light brown, milk chocolate like color.
- A black, dry, and zooty looking spark plug may indicate a rich fuel mixture. Carbon deposits cause this color.
- Sandy looking oil deposits built up primarily on the outer electrode may indicate bad valve seals causing oil to be sucked into the engine.
If your spark plugs are old or do not fit the description of a healthy spark plug, it needs replacing. Your user manual will tell you the correct type of spark plugs to use.
The intake boot is damaged or not seated properly
The rubber intake boot on the carburetor may have cracks or may not be seated properly. When this happens, the air/fuel mixture will be off, preventing the ATV from running correctly at idle.
The fuel lines or fuel filter may be restricted, clogged or kinked
The carburetor needs to have an unrestricted gas flow for the ATV to idle correctly. Any restriction in the gas supply can cause idling issues.
Ensure the fuel lines are not clogged or bent so that they do not allow proper fuel flow. Replace any clogged or damaged lines and make sure they are correctly installed with no kinks.
If your bike has a separate fuel filter, it may be clogged up from years of riding or contaminated fuel. Replace the filter with a new one. You should find it if you trace the fuel line from the gas tank to the carb.
To test the fuel-flow going to your carb, you can place a container underneath it and loosen the carb bowl drain screw for a few seconds. If there are no restrictions, you should see an unrestricted flow of fuel running into the container.
Now that you have determined proper fuel flow to the carb, you can shift your focus to the fuel delivery inside the carb.
The carburetor is dirty and needs to be cleaned
Carburetors can get dirty and clogged from using fuel contaminated with dirt, having a missing or improperly fitted air filter or from old fuel.
When the carburetor is dirty, the ATV may not be getting enough fuel to run correctly, either when riding or at idle.
ATVs that sit a lot are particularly prone to gumming up. Gasoline starts breaking down after just three to four weeks, forming polymers (unstable hydrocarbon fuel molecules), also known as varnish. The varnish can be seen as a sticky, caramel color substance covering the inside of the tank, the fuel lines, and carburetor.
Using ethanol-based gasoline adds to the problem by acting as a solvent that dissolves old gum and varnish deposits from the fuel lines and from the gas tank.
Inside the carburetor, there are a couple of brass jets that must be clean to allow proper gas flow through the carb. When the deposits enter the carburetor, it can clog the tiny opening in the jets.
A gummed up carburetor can often be cleaned to working order by running through a couple of tanks with a carb cleaner such as SeaFoam added to the fuel. Follow the instructions provided with the product.
If that doesn’t improve gas flow, you will need to disassemble the carburetor for a more thorough cleanse.
- Drain the carb into a container by opening the drain plug at the bottom of the bowl.
- Remove the carb from the ATV.
- Disassemble the carb, begin by removing the bowl. Take note of where everything goes; it is easy to get lost if you are inexperienced with disassembling carbs.
- After disassembling the carb, carefully remove the main jet. Remember, they are made out of brass, so be careful not to damage the fragile threads.
- Then remove the pilot jet (the idle jet). The main jet has a larger diameter and does not clog up as quickly as the pilot jet.
- Soak everything in a small container of gas or cleaning solution
- Use a small needle and an air compressor to clean the jets. Reinstall and check if this helped.
NOTE: Disassembling and cleaning a carb is not for everyone. If you’re not able to fix the problem, or do not wish to attempt at disassembling it yourself, you can have the carb professionally cleaned and rebuilt by a dealer.
The fuel injectors are dirty
Fuel-injected ATVs do not have carburetors with jets. Instead, they use fuel injectors that are nozzles with tiny openings. Fuel injectors can clog up from carbon as a by-product of the combustion process.
Clogged up fuel injectors can be cleaned by a mechanic, using a combination of a powerful solvent and high-pressure air. Before taking your bike to a mechanic you can try cleaning the injectors by using a fuel additive such as Techron or similar.
The fuel cap may not be venting correctly, or the fuel tank venting system is blocked
The fuel tank on your ATV has a vent that allows air to enter the tank as the fuel level decreases. It can be in the form of a separate venting system, or the vent can be located in the gas cap itself.
If this vent for some reason gets blocked or stops working, you will get a vacuum inside the tank, and the carb or fuel pump will no longer be able to pump fuel out from the tank.
Try loosening the fuel cap to see if this resolves the issue. If it does, you need to investigate further to locate your flocked tank vent.
If the bike has a separate venting system, make sure it is not blocked with mud or has a breather tube that is kinked or otherwise damaged.
Sometimes it may be hard to identify a faulty vent. In such cases, your best option will be to replace the tank cap.
The gas is contaminated with water
If the ATV has been sitting outside through a heavy rainstorm, if the gas cap does not seal properly or the bike is submerged underwater, the gas in the tank may become contaminated with water.
This is how you repair an ATV that was submerged in water.
On a carbureted ATV, you can try draining the carb to see if there is any water inside. Water is heavier than gas and will sink to the bottom of the carb.
Open the bleed screw located at the very bottom of the carb housing, and let the contents flow into a small bucket. If there is any sign of water, you likely have water inside your gas tank as well.
Thoroughly drain the gas tank and add fresh gas to see if that fixes your issue.
The carburetor needle valve is stuck closed in the float bowl
Inside the carburetor, you have a bunch of small components that can get damaged or stuck, which will affect how well the ATV runs.
One of the more common culprits is the needle valve under the float. If the carb is dirty, or if the needle is bent, it can get stuck, preventing the float from letting any more fuel inside the carburetor.
To test this, gently tap the carburetor housing with the engine running at idle. Then try putting the bike in gear and ride it. If gently tapping solved the issue, you may get away with cleaning the carburetor with SeaFoam.
In more extreme cases, you may need to disassemble the carb for a proper clean and to install a carb repair kit.
Polaris ATVs with ETC (engine throttle control) switch: The throttle cable is adjusted incorrectly
Some Polaris ATVs have a so-called ETC switch that works as a safety feature for when the cable breaks, binds, freezes stuck, or for some other reason, doesn’t retract completely.
The design originally comes from the snowmobile industry, where it was added to shut off the engine if the throttle cable freezes shut in a wide-open throttle position. It is also designed to shut off the engine if the throttle cable breaks at full throttle, or if it gets stuck and will no longer slide freely.
Inside the switch, there are two metal connectors that generally should not touch. If there is not enough slack in the throttle cable, the connectors may touch too soon, tricking the ATV to shut off when it is supposed to idle.
Adjusting the free play of your throttle cable is quite easy. Please refer to the user manual of your specific bike for the correct adjustment procedure. Correct throttle cable free-play is typically 1/16 to 1/8th of an inch.
Valve clearance or valve timing is off
If the ATV doesn’t idle well or often stalls after cold starts, but runs fine as soon as it warms up, it may be worthwhile having the valves inspected and adjusted.
The rough idle may be caused by a valve that is opening too late, choking off fuel.
When the engine keeps stalling or bogs down or stalls when applying throttle
When the engine idles fine but won’t rev up, it is a sign of it getting too little fuel, but can also be because it is getting too much fuel.
The ATV may run fine at low speeds, but as soon as you apply a little or a lot of throttle, the engine will bog down and turn off. If you let the bike sit for a few minutes, it will typically start again, just to repeat the same behavior.
Note that all of the fuel and air-related issues listed above may also apply for an ATV that bogs down when applying throttle. The bike may be getting enough fuel to idle, but not enough to keep up with hard acceleration.
Here are some potential culprits to look into:
Carburetor related issues
- A broken needle jet may cause the bike to run at wide-open throttle as soon as you rev it, causing it to flood out.
- A cracked or punctured float will leave it full of fuel, not allowing it to float and do its job.
Low fuel pressure due to a bad fuel pump
Fuel-injected ATVs can get low fuel pressure for many reasons, most commonly due to a bad fuel pump.
Turn the ignition on (but do not start the bike) and notice whether you can hear the pump charging and if it sounds healthy. The pump should activate for a few seconds to prime the system with fuel.
To further test the fuel pressure, you need a fuel pressure gauge. If you don’t have one, it is best to leave this job for a mechanic.
The fuel pump is located inside the fuel tank. If it is bad, you usually need to replace the whole fuel pump assembly at about $700 to $900. If you are somewhat mechanically skilled and want to save a few dollars, it is possible to replace the pump itself. You can get a decent pump for around $70 to $100.
Other causes of low fuel pressure
- A faulty ECU (engine control unit)
- A faulty TPS (throttle position sensor)
- A faulty MAP (manifold absolute pressure) sensor
- A faulty pressure regulator
- Fuel injector issues
- Various other sensor issues such as loose or broken sensor wire connector pins/sockets
We recommend that you take the ATV to your dealer to help troubleshooting issues like these.
Vacuum petcock not working properly
Vacuum style petcocks are particularly prone to failing, not letting gas out of the fuel tank.
Inspect the vacuum line that goes from the intake manifold to the petcock for damages, kinks, or coming loose.
Inside the petcock, there is a rubber diaphragm that may go bad. Also, make sure the carburetor vent line is not plugged.
When the ATV starts but will only stay running for a short time
In this scenario, the ATV will start just fine but shut after a short time, whether at idle or when applying throttle.
Electrical components overheating
Electric ATV components such as the stator, pick-up coil, CDI, and regulator are not as reliable as we would want. If these components go bad, they may be heating up, causing the bike not to run correctly as soon as they reach a specific temperature.
Typical behavior when having electrical issues like this is that the bike starts and runs fine for 5 to 15 minutes before it starts acting up. Then if you let it cool down, it will run fine for another 5 to 15 minutes.
Valve clearance or valve timing is off
Just as when your bike is having a hard time idling, incorrect valve clearance or timing may cause the ATV to shut off when it gets warm.
The fuel/air mixture is not set correctly
If the bike is acting sluggish and sputtery, it’s a sign of the air/fuel mixture being too rich. Make sure the jetting is set up correctly and consider a re-jet.
Blocked air filter causing the bike to run rich
A partly blocked air filter is another possible cause to look into when the bike sputters and shut down as soon as you apply throttle.
Remove the air filter to see if this makes the bike run properly again. If so, you need to replace the filter even if it does not look dirty.
Make sure there is no moisture or snow in the airbox, as this may clog the filter. Dry out any moisture completely and let the filter dry before installing the filter again.
If your ATV uses an oiled foam style filter, you need to clean it and apply new oil. Make sure not to use too much oil as this may restrict airflow.
Partzilla has an excellent video on how to clean and oil a foam-style ATV air filter.
Fuel issues on cheap 50-110cc youth ATVs that won’t stay running
Cheap Chinese ATV youth ATVs of lesser-known brands are notorious for not running properly after a while. More often than not, you will find that the issue is carburetor related.
Most of these cheap ATVs use cheap knock-offs of a VM 19mm style carburetor to keep costs down. While the carb may look fine at first glance, you will often find that they are made from inferior materials with poorly crafted jets.
When a carb this size gums up, they can be tricky to disassemble and clean. If you know your way around carbs, you may give it a go, but if you’re not, you are most likely better off getting a new, original replacement carb.
The same size original carb should bolt straight on, and will likely save you from a lot of agony down the line.
Even if you cannot track down an original carb, a new cheap knockoff is still a better option than fighting with the gummed up one you have. They only cost about $30.