It’s not uncommon for ATV owners to 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 their ATV starts and runs fine, but only briefly before it shuts off.
In this post, we will look at the most common issues to look into when your ATV keeps turning off.
For easier troubleshooting, I’ve categorized potential issues based on the specific behaviors exhibited by the ATV.
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 your machine’s specific behavior.
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 usual or is slightly hard to start.
- It may run as usual when you ride it, but you may also have difficulty 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 the engine’s idle RPM. The carburetor will not provide enough gas to keep the engine running whenever it is set to low.
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 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 sooty-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 poor valve seals causing oil to be drawn 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.
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.
Restricted, Clogged, or Kinked Fuel Lines or Fuel Filter
The carburetor must 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 ensure 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, 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 the 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
A carburetor can get dirty and clogged from using fuel contaminated with dirt, missing or improperly fitted air filters, or old fuel.
When the carburetor is dirty, the ATV may not get 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 the 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 the gas tank.
Related: How to Know if the Gas in Your ATV Is Bad or Not
Inside the carburetor are a couple of brass jets that must be cleaned to allow proper gas flow through the carb. When the deposits enter the carburetor, they can clog the tiny opening in the jets.
A gummed-up carburetor can often be cleaned to working order by running 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 must 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 inexperienced with disassembling carbs.
- After disassembling the carb, carefully remove the main jet. Remember, they are made 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 cannot fix the problem or do not wish to attempt to disassemble 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 powerful solvent and high-pressure air combination. Before taking your bike to a mechanic, you can try cleaning the injectors using a fuel additive such as Techron or similar.
Fuel Tank Not Venting
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.
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 must 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, replacing the tank cap will be best.
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 if the bike is submerged underwater, the gas in the tank may become contaminated with water.
Related: This is how you repair an ATV that was submerged in water.
On a carbureted ATV, 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 at the bottom of the carb housing, and let the contents flow into a small bucket. If there is any sign of water, there is likely 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
Inside the carburetor, specific small components can become damaged or lodged, impacting the performance of the ATV.
One of the more common culprits is the needle valve under the float. If the carb is dirty or 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 riding it. If gently tapping solves the issue, you may get away with cleaning the carburetor with SeaFoam.
In more extreme cases, you may need to disassemble the carb for proper cleaning and install a carb repair kit.
Polaris TVs With ETC Switch: Incorrectly Adjusted Cable
Some Polaris ATVs have a so-called ETC (Engine Throttle Control) 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 are two metal connectors that normally should not touch. If there is insufficient slack in the throttle cable, the connectors may connect too soon, tricking the ATV into shutting off when it is supposed to idle.
Adjusting the free play of your throttle cable is relatively 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 a cold start but runs fine as soon as it warms up, having the valves inspected and adjusted may be worthwhile.
The rough idle may be caused by a valve opening too late, choking off fuel.
When the Engine Bogs Down or Stalls When Accelerating
When the engine idles fine but won’t rev up, it is a sign that it is getting too little fuel, but it can also be because it is getting too much fuel.
The ATV may run fine at low speeds, but when 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 back up again, only to repeat the same behavior.
Note that all fuel and air-related issues listed above may also apply to 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 engine) and notice whether you can hear the fuel pump charging and if it sounds healthy. The pump should activate 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, leaving this job for a mechanic is best.
The fuel pump is located inside the fuel tank. If it is defective, you usually need to replace the entire 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
I recommend taking the ATV to your dealer to help troubleshoot issues like these.
The Vacuum Petcock Is Not Working Properly
Vacuum-style petcocks are particularly susceptible to failure, preventing gas from exiting the fuel tank.
Inspect the vacuum line 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 Only Runs Briefly
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 less reliable than 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 difficulty 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 signifies the air/fuel mixture is 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 ATV sputters and shuts down as soon as you apply throttle.
Remove the air filter to check if this helps. If so, you must replace the filter, even if it doesn’t appear dirty.
Ensure no moisture or snow is in the airbox, as this may clog the filter. Dry out any water entirely and let the filter dry before installing the filter again.
If your ATV uses an oiled foam-style filter, you must clean it and apply new oil. Ensure not to use too much oil, as this may restrict airflow.
Partzilla has an excellent video on cleaning and oiling a foam-style ATV air filter.
Fuel Issues on Youth ATVs That Won’t Stay Running
Cheap Chinese ATV youth ATVs of lesser-known brands are notorious for not running well after a while. More often than not, you will find that the issue is carburetor related.
Most of these cheap ATVs use knockoffs of a VM 19mm style carburetor to keep costs down. While the carb may look fine at first glance, you will often find they are made from inferior materials with poorly crafted jets.
When a carb this size gums up, it 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 exact size original carb should bolt straight on and will likely save you from much agony.
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.
FAQ
Why won’t my ATV stay running?
An ATV might not stay running due to various issues, including bad fuel, a dirty carburetor, or a faulty spark plug. Regular maintenance is key.
Why does my ATV die at idle?
If your ATV dies at idle, it may be due to an improperly adjusted idle screw, a clogged carburetor, or a faulty fuel/air mixture.
Can a dirty air filter cause an ATV not to idle properly?
Yes, a dirty or clogged air filter can restrict airflow, causing poor idling and possible stalling in an ATV.
Wrapping Up
Remember that troubleshooting ATV issues can be a complex task, requiring both mechanical knowledge and patience. It’s important to thoroughly examine all potential problem areas and perform the recommended maintenance and checks.
If you still experience difficulties, don’t hesitate to seek professional assistance to ensure your ATV runs smoothly and safely.
