Picture this: You just got back home from an intense ATV trail-run when you notice that the exhaust is glowing red hot. You naturally start worrying whether this is normal or not.

A glowing red color is usually an indicator of fire-bursting temperatures, which is rarely a good sign, especially when it involves our expensive toys!

Any ATV will generate a lot of heat when you push it to its limit. And this heat needs to go somewhere.

When something is preventing the bike from getting rid of this heat as it is supposed to, or if some issue is making the bike produce more heat than it is designed to handle, heat will start building up in the exhaust system.

What is a glowing red hot exhaust after all?

The exhaust glows red when the metal heats up to where it’s getting closer to its melting point. But there is no risk of the metal actually melting, as this requires quite a bit more heat, even from the point where it is visibly glowing red.

The glowing happens at different temperatures, depending on what type of metal your exhaust is made of. Stainless steel, for example, will glow at a much lower temperature than non-stainless.

So determining the actual temperature solely by the color of the glowing is not very accurate. A temperature gauge is needed to get the correct readings.

During the day, you will in most cases, barely be able to see the glowing. And if you do it will look more like a dark red. But in the dark, the same temperature will make it glow bright orange.

Does a red-hot exhaust always mean something is wrong?

Before we get into the actual causes for why your exhaust may be glowing, you should know that some glowing is perfectly normal on many ATVs.

The first part of the header, or up to the first bend of your bike’s exhaust, may start glowing if you push it hard enough. This does, however, not necessarily indicate something is wrong with the bike. It will not hurt anything.

But if the exhaust glow beyond the first bend, you probably have a problem that needs to be addressed.

I cannot tell you what is normal on all bikes, so if you want to be entirely sure everything is ok, your dealer should be able to tell you how your specific bike should behave.

However, if the color suddenly starts changing, it’s a good indicator that something is not right.

If you know that before, just the first few inches of the exhaust usually became slightly red. But then one day you notice a lager part of the pipe is affected, and the color has changed to bright orange, almost white color.

This means something has changed, and it would be a good idea to locate what’s causing this change before it gets any worse.

So let’s dive into the potential causes for your glowing exhaust.

Reason 1: The bike is running too lean

If the bike for some reason does not get as much gas as it needs, it will still run, but it will be running too lean. This condition where the bike does not get enough fuel and too much air can cause a furnace effect.

This will generate more heat, with a glowing exhaust as the most visible consequence. Another possible consequence of running the bike in this condition is that it over time will burn a hole in your aluminum piston.

In the worst case, you end up with completely seizing the piston, leaving the cylinder kit pretty much unusable.

After reading countless forum posts, articles, and other sources on the topic, I dare claim that the bike running too lean is the most common reason for glowing ATV exhausts.

To complicate things even further, there are a handful of possible causes for the bike to be tunning too lean.

How to tell if the bike is running too lean?

There are several ways you can go about determining whether the bike is running too lean or not.

Start by taking it out for a couple of passes. If the bike, when you let off the throttle, make loud and hard popping/cracking sounds, almost like firecrackers, it is likely to lean on the idle/pilot circuit.

This popping is often referred to as the bike backfiring. And while some popping is perfectly normal, you may want to look into it if it gets very loud and hard.

Loud backfiring is usually a good sign of the ATV running too lean.

Another way to tell if the bike is running too lean, just by riding it, is the idle hangs. What this means is when you let go of the throttle, the RPMs does not drop immediately as you would expect. Instead it “hang” for a bit on higher RPM’s. The bike may use several seconds to get itself back down to idle.

A more mechanical approach to telling if the bike is running too lean is by inspecting the spark plug(s)

  1. Start by taking the ATV for a spin to get it up to running temperature
  2. Then remove the spark plug to clean it. Use a copper wire brush and a rag to get it completely clean. Be careful not to bend the metal arch as this will damage the plug.
  3. Also wipe down the area around the cylinder head, using the rag. Be careful so you don’t get any debris inside the cylinder.
  4. Reinstall the spark plug and go for a short ride of only a couple of hundred meters on full throttle. Ideally, this should be done uphill to add even more load.
  5. Stop and remove the spark plug. Use a glove and be careful, it is very hot!
  6. Inspect the plug. If the bike is running to lean, you should see a white-ish color on the tip of the plug, and there should be no visible moisture (oil or gas). If the bike is running extremely lean, you will notice the tip of the plug starting to melt. If the plug, on the other hand, is slightly wet but otherwise clean, your settings are likely good. The color should be grey to brownish with little zoot.

Running lean because of dirty carburetor or jets

So you’ve determined that the bike is running a bit on the lean side. If the bike is otherwise stock, you should start by cleaning the carburetor to eliminate the chance of a plugged or partially plugged jet.

Remove each jet to clean them individually. Use spray cleaner, a copper brush, and compressed air to make sure they are completely open. Soaking them in a cleaner is often not enough to get a good result cleaning the tiny passages, especially for the pilot jets.

Dirty pilot jets would also cause lean idle problems.

Running lean because you have the wrong or non-ideal jetting

If you’ve determined that the jets are clean, you may need to change them up a size or two to allow a higher flow of fuel.

Be aware that many ATVs run a bit lean from the factory. They are set up like this on purpose to meet some of the emission standards.

Buy and install a jet kit and won’t be surprised if your glowing exhaust improves by quite a bit, if not completely disappears.

Running lean because of cracked vacuum lines

Damaged vacuum lines will also make the bike running lean. These are easy to visually inspect, as well as fast and cheap to replace.

Reason 2: Dirty, damaged or poorly adjusted exhaust valves

The exhaust valves inside your engine have the important job of closing when ignition happens, then to open to let the exhaust gasses out on the next stroke. This process happens continuously at high speed when the engine is running.

Over time, carbon residue may build up on the valve head, making for an un-tight seal. This will allow hot air and flames from the explosion to exit through the gap when the valve is supposed to be completely closed.

The same is true if the valve is (very) poorly adjusted, or even damaged, making it not close the exhaust port completely when it should.

Both of these issues require the cylinder head to come off for inspection, adjustment, or cleaning. If an oil-change freaks you out, now would be a good time to give your mechanic a call.

To test if your valves are good, you can try performing a compression test. The compression should be lower than manufacturer specs.

An even more accurate way is to perform a so-called leak-down test.

Reason 3: Exhaust leak

Exhaust leaking before it exits the system will result in a lower back pressure, which in turn may cause the bike to run hot.

Look for loose clamps, damaged donut gaskets or even holes or cracks in the pipe. Repair or refit to see if this improves things.

Donut gasket on Polaris XP-1000 aftermarket exhaust.

Reason 4: Aftermarket exhaust headers or exhaust systems

Aftermarket exhaust systems and headers are usually made of different materials than stock systems. As we’ve already looked at, a system made of stainless steel will glow at lower temperatures than non-stainless.

On top of that, they usually use thinner walls to save weight. This means less mass to take up the heat, with more glowing as a result.

On the other hand, aftermarket systems will usually give you much better exhaust flow. This allows for the heat to exit the system much faster, making for an overall much cooler system.

Reason 5: No airflow when standing still idling

The only cooling the exhaust system will get is by the air passing by when you are moving.

When the bike is standing still, so will the air around the exhaust, and there will be almost no cooling. This makes it much harder to keep the temperature of the header and the exhaust down.

Even if the bike produce more heat when riding, you may even find that the glowing gets worse when standing still at idle. This shows how important the airflow is to keep the system cool.

So if your exhaust is glowing red when standing still at idle, it may just be because of too little cooling.

Reason 6: Clogged pipe or muffler

If something is restricting airflow somewhere in the exhaust system, you” get excessive back pressure where heat will build up instead of escaping as hot air.

Luckily, this one may be a cheap and easy fix that should be ruled out early in the troubleshooting process, before you start looking into the more serious causes.

Start by having a look into the end of the rear muffler. If the bike has a spark arrester fitted it may have become dirty and needs a good cleaning so it won’t restrict airflow.

Also, look for mud or some other debris clogging the pipe. If you’ve been riding in deep mud and you’ve stopped the engine, mud may have gotten inside the system. In this case, you need to disassemble everything to clean the inside of the exhaust.

If the bike has been parked for some time, you should also consider the possibility that some critter has made a new home of your exhaust. Mice tend to like dark cozy places when they are nesting to give birth. Your bike may have been it’s chosen the perfect spot.

I’ve not had this happen with mice, but when we start preparing the different implements on the farm at the springtime, it’s common to find birds nests in the strangest places.

Because of very strict sound emission regulations, bikes that are sold in my home country (Norway) are often fitted with extra large and stuffed mufflers, compared to US markets. The exhaust flow suffers badly from this, keeping the heat trapped inside the exhaust system.

Story-time:

On a friend of mines XP-1000, flow restriction had the unfortunate effect of setting the bike on fire!

He was riding at low speeds, hauling a moose out of the woods, using an ATV trailer. The exhaust got so warm that the plastic ignited.

Polaris Sportsman XP-1000 caught fire because of a glowing hot exhaust.

Luckily he had water available and was able to put out the fire before it spread. The dealer wanted to solve the issue by adding more heat-chields.

He rather chose the option of installing an aftermarket exhaust, allowing for much better airflow. The glowing exhaust disappeared immediately.

Reason 7: Bad thermostat

This is probably not the most common reason to why your exhaust is glowing, but if you are experiencing heat-issues it’s always a good thing to make sure the thermostat is functioning as it should.

A properly functioning thermostat will open at a given temperature, allowing coolant to flow through the radiators in the cooling system.

These things, however, are prone to fail because of corrosion or other various reasons. Luckily they are cheap and easy to replace. So when in doubt, you don’t waste by installing a new one, even if it is not the cause of your issues.

Thermostat.

The coolant does not cool the exhaust directly, but it keeps the overall engine temperature low. When the system is not functioning properly, you will get a higher engine temp, resulting in a bigger chance for a glowing red hot exhaust system.

To test the thermostat, you simply disassemble it and bring it over to your kitchen. Its best to do this job when you are home alone and don’t risk having to explain yourself to a skeptic spouse.

Put the thermostat in a casserole with clean water and heat it until it boils — no stirring necessary. You should be able to see clearly when the thermostat opens, usually just before the water starts boiling.

If you have the specs for your thermostat, you can use a thermometer to see if it opens at the correct temperature.

If nothing happens, it is bad and needs replacing.

Reason 8: Something disturbing intake airflow

Check if something is obstructing free airflow through the airbox. Also, have a look at the intake boots and inspect for any cracks or loose clamps that could give you an air leak.

The rubber boot between the carburetor and the cylinder is also prone to cracking when it starts aging. If it’s cracked, it’s best to replace it.

A temporary fix I’ve used with good results is putting some Tec7 Multibond in the crack until I could get a hold of a replacement. Do not ride the bike until the sealant has healed completely.

Reason 9: Weak or intermittent spark

If the spark is too weak or if it’s intermittent you won’t burn all the fuel, and you get incomplete combustion If the unburned fuel does not ignite until it enters the exhaust a red-hot exhaust is to be expected.

Reason 10: Glowing in the winter

When temperatures are low, the air will be more dense, causing the ATV running in a more lean state.

If the bike was already running a bit on the lean side in the summer, using it in the winter may be what tips the scale for it to be running too lean.

Fuel-injected bikes should not have this issue as they automatically compensate for different operating temperatures. But if your bike is equipped with a traditional carburetor, it may be worth looking into.

If this is the case, you may need to re-jet the bike. An alternative to having to change jetting between summer and winter conditions is to set it up to run a bit rich in the summer.

This should ideally allow the quad to run fine all year round.

Reason 11: Wrong type of spark plugs installed

Using the wrong type of spark plug may have your engine running hotter than it’s supposed to.

Different spark plugs operate at different temperatures, so it’s crucial to get the right ones according to your bike specs.

You will find the correct numbers in your owners manual.

Reason 12: Bike running too rich

This one is almost a non-issue nowadays when we have fixed jettings.

But back in the days when we had adjustable main jets, you could possibly mess up the adjustments so bad that unburned fuel was sent down into the muffler where it would continue to burn.

In this case, your muffler would glow like the sun on a hot summers evening