An ATV that won’t idle when the engine has been warmed up can be due to many things.
The most common reason for an engine to not idle when warm is often from the choke not set right, valves needing adjustment, to even the very rare one like battery cables – yeah, it’s possible.
I’m going to list all the possibilities and what to do if your ATV or side by side won’t idle when the engine is hot.
1. Check The Choke
If you have a carbureted ATV engine, you’ll have a choke.
If you have a fuel-injected engine, you won’t have a choke; there is no lever to pull when starting it; you just put the key on and press the start button.
The choke is needed when starting a carbureted engine. But once the engine is warmed up, the choke is not required, and keeping it engaged will stall the engine.
So make sure to push the choke cable in once the engine has warmed up. The choke cable is only for starting the engine when it’s cold.
Also, make sure your choke cable isn’t binding on something, and it’s not stuck either.
Sometimes the cable can get wrapped around something else and force the cable to stay engaged.
Or, over time, the cable can break from rusting or wear out and can be stuck in the closed position. The ATV will start fine, but once it gets warmed, it will stall out as the choke is blocking too much airflow.
2. Check The Valves
An ATV that won’t idle when it’s warm can often be traced to the valves being out of alignment.
You have intake and exhaust valves, and if they’re not set to spec, it can cause idle and running issues.
Adjusting the valves is an involved process, especially if you have never done anything like it before. For most people, it’s best to take it to the dealership and let them do it.
If you have the skills, you can do it, but you’ll need to look up the specs for your exact ATV.
3. Change The Spark Plugs
If I have an ATV with running problems, one of the first things I replace is the spark plugs.
You’ll be amazed how many machines can be fixed by just replacing the spark plugs.
I’ve gotten to the point where I change my spark plugs every 2 years, sometimes every year, if I’m looking for something to do. It’s an easy thing to do, well, on some ATVs, but it keeps away a lot of headaches later.
And don’t half-do it; I know some guys that will only change one spark plug because the other one is hard to get to. Always change both spark plugs at the same time or don’t change them at all.
4. Gummed Up Carb
If you have a carbureted ATV engine, the carburetor itself can get gummed up and cause all kinds of running issues.
Taking the carburetor out and cleaning it will fix many running issues, especially if the ATV has been sitting for a while.
You can try putting in some fuel system cleaners to see if it fixes it, so you don’t have to take the carburetor out and clean it. Of course, cleaning the carburetor is more of a sure bet, but I’ve gotten lucky a few times with some fuel system cleaners.
5. Check The Spark Arrestor
A spark arrestor is common on ATVs and side by sides; it’s to keep “flames” from your ATV from blowing out the exhaust.
It’s a big problem when riding in the woods as it can cause forest fires.
The spark arrestor is a simple piece of metal mesh with many holes located inside your muffler.
These small metal holes can get clogged with carbon from the exhaust of your ATV. If too many holes are clogged, it can cause running issues.
Cleaning out or replacing the spark arrestor can fix many running problems you may have, especially if the ATV won’t idle when the engine is hot.
Do not run your quad without the spark arrestor in place!
6. Check Air Filter
A dirty or clogged air filter can cause idle problems, though it causes more of a problem for an engine to start and keep going.
It’s not uncommon for an over-oiled filter to cause idle problems when the engine is warmed up as the oil reacts to being warm.
Make sure you don’t over oil your air filter.
While it’s not best to run your engine without the air filter, you can determine if the air filter is the problem by leaving it off for a few seconds to see how the ATV responds. Just don’t go for a ride without the air filter, and don’t do this test in a dusty location either.
7. Check The Fuel
If the ATV or side by side has been sitting for months, it’s just better to assume the gas is bad.
If you’re not putting fuel stabilizer in your gas tank when letting it sit for months, the gas goes bad and bad gas can clog the carburetor and cause all kinds of running issues.
Get rid of the bad gas safely and carefully and put some fresh gas in your ATV.
8. Check Fuel Lines
For both carbureted engines and fuel-injected engines, check the fuel lines for any damage or cracks.
But for carbureted models, see how it runs when you move the fuel selector to RESERVE instead of ON.
I’ve seen bad fuel lines cause an engine to have running issues, but moving the fuel selector to reserve often fixes it. This is because people don’t use reserve as much, so the lines stay cleaner.
If your ATV runs fine while only on reserve, you need new fuel lines, and a carb clean won’t hurt either.
9. Check Your Wiring
This is an odd one as it’s rare but check your wiring, especially your battery cables.
I had an ATV that started and ran fine until the engine got hot, and then it would just shut off as if someone flipped the kill switch.
As the engine warmed up and got hot, it caused other things to expand too, and I’ve seen connections that were already loose get even looser and cause the ATV to shut off or act oddly.
I’ve also seen a battery cable routed the wrong way and was touching metal, and as the metal got hot, it melted the rubber on the cable and shorted the battery out, and shut the engine off.
Make sure cables are not rubbing on metal, especially the thick battery cables, as the heat and rubbing will cause all kinds of problems for you.