Why your ATV is Smoking, and how to Fix it

There’s nothing as fun as ripping through the mountain side on a quad, but that can go downhill in a hurry when something goes wrong with your ATV.  While ATVs tend to be very resilient machines, things do go wrong, and one of the most common causes for concern is when your quad starts smoking. It can be gut wrenching if you don’t know what is wrong.  Having had that feeling, I researched all I could to figure out what causes smoke so I would always have a good grasp on the cause.

Why do ATVs smoke? Smoke can be an indication of bad cylinders, seals, gaskets or something similar, usually accompanied by gasoline or oil burning in the engine.  The cause isn’t too hard to figure out based on the timing and color of the smoke.

When faced with a smoking four wheeler, don’t continue riding.  Routine maintenance helps prevent many smoke-related issues, but a hard crash, bad cylinders or other causes may lead to serious problems in your ATV. Fortunately, the color  and timing of the smoke coming out of your quad will help narrow down the problem so that you can find a solution and get back to the trail.

Because smoke is a good indication something needs repaired, be sure to check out our guide to the cost of most ATV repairs so you know how much it should cost and whether you should do it yourself.

What the Timing of the Smoke Tells You

If the smoke only occurs when you start your quad, but doesn’t happen during the ride, there is nothing to worry about as it is just condensation burning off.

If the smoke is excessive early in your ride, but then goes away later on, you are most likely dealing with bad piston rings or valve guides/seals. When the ATV is is warmed up, the oil burns off better, and the smoke goes away.  In this situation, it is best to do a compression test and a leak down test.  Similarly, if the smoking happens primarily when you are revving your engine, that is likely a sign of bad rings.

If the smoke is predominantly happening when you are letting off the gas, this could be a sign that rings are not hitting the adjacent walls perfectly.  This isn’t a huge issue. Now if the smoke stops when you let off the gas and starts back up when you hit the gas again, I would look at the valve seals first.

What do the Colors Mean?

The color of smoke coming out of your ATV tells you a lot about what is causing the smoke.  It won’t tell you everything, but it will tell you where you need to look and how concerned you should be.  ATV smoke usually comes in one of four colors: white, gray, blue or black.

White Smoke

White smoke is usually the best kind of smoke you can hope for.  A little white smoke when you start your ATV can be perfectly normal.  That is water vapor burning off. It is not a bad sign of anything in your engine, so long as it burns off in the first 30 seconds or so.

If the white smoke doesn’t go away after the first minute, or if your ATV starts puffing out white smoke in the middle of your ride, well that is no longer nothing to worry about.  At that point, there is a decent chance coolant is burning in the combustion chamber.

Coolant can leak into the combustion chamber to burn from a handful of problems, including a damaged radiator, damaged radiator hose, blown head gasket or a broken water pump.  The easiest way to determine if there is a problem in your radiator system is to check your coolant level. If there is a leak, the coolant will be low and you smell a sweet odor coming from it.  You should then put your ATV in neutral and rev the engine.

If you get a lot of white smoke, that is a bad sign something is wrong with the radiator system that needs to get checked out. You need to address it immediately too, as it continuing to run the quad in this condition will cause overheating that leads to more and more issues.  

I’ve been lucky to never have this in an ATV, but in college, I let a friend borrow my car. When he returned it, he mentioned that the engine had smoked a little while climbing a hill. Rather than check it out, he kept driving for several hours. By the time I got it back, the head gasket was blown and the radiator ruined. Several hundred dollars later, I gave up and junked the car.

Black Smoke

Black smoke is almost always an indication that there is something bad happening.  Black smoke is a sign that your ATV is burning gasoline. Gasoline burns in your ATV when the ratio of fuel to air is higher than usual.  This is called a rich fuel environment, and it is not good for the ATV.

Fixing a rich fuel environment could involve a number of things.  Hopefully, for your sake, it is nothing major and calls for a simple fix.  Some of the easier-to-fix causes of black smoke include the following:

  • A leaking fuel injector.  This is a really easy fix.  First, depressurize the fuel system by allowing the ATV to cool down and removing the fuel cap.  Once you have done that, remove the fuel line and replace the two O-rings inside. Turn the electricity on to your ATV (but don’t actually start the ATV cause it could go boom) and check to see if there is any leaking in the fuel pump.  If that didn’t work, then you’ll have to replace the fuel injector
  • A leaking carb float needle or seat.  This can happen when gasoline is left sitting for too long in the carburetor.  Oil that smells of gasoline is a sign of gas contamination from a faulty float valve. Luckily, this is a pretty easy and cheap fix.  To inspect a float needle, remove the pivot pin and float. Often the needle will come out with the float. Check the float to see if any fuel has worked its way inside the plastic float bodies. Replace the floats if they have fuel in them.  If that means nothing to you, a simple google search will reveal the process.
  • Clean or replace the air filter.  This is the best-case scenario. Air filters in an ATV get crazy dirty, much worse than on your car or truck  You are riding in dirt, dust, mud, water and so forth. That filter needs to be cleaned and/or replaced often As it clogs up, your ATV will lose power and it can also result in some black smoke.  If you have a paper filter, just knock off all the gunk you can until it looks mostly clean. If you can’t get it cleanish or if there are tears in it, then it’s time to get a new filter.  If you have a foam filter, soak it in some cleaning solution and gently remove all the gunk.  After that, let it dry, oil it up, then let it rest for a couple hours before hitting the trails.
  • Improper valve clearance.  This is a pretty common cause of black smoke that is discernible due to the noise you can hear coming off your cylinder heads.  All that bumping and shaking during a ride can mess with the valve clearance on your ATV. Use a feeler gauge to check for the clearance level, and get it fixed if it is off.

If it isn’t being caused by one of the above issues, you are likely looking at something more complicated.  The causes of black smoke you are hoping to avoid include the following:

  • Faulty fuel injector/carburetor.  The easiest way to test for a bad fuel injector is to check the temperature of your engine cylinders while the ATV is running.  If one or more cylinder is running hotter than the others, that is a pretty good indicator you will need to repair or replace your fuel injector.
  • Engine block overheating  If you don’t handle this quickly, you will likely end up needing to rebuild your whole engine.  More likely than not, an overheating engine is caused by the radiator system. Usually, this causes blue smoke (see below), but once in a while, it can appear to be black smoke.
  • Faulty controller  While you may think there is a problem with the fuel injector, it may actually be the controller that has the problem.  

Blue (or Blue/Gray) Smoke

Whereas black smoke means you are burning gasoline, blue smoke means you have burning oil. This may not be a big deal if you have a 2-stroke quad since such engines normally emit a blue/gray smoke. If you have a 4-stroke quad with blue smoke, or your 2-stroke is putting off an excessive amount of blue smoke, then you have a problem.  The more rapidly your ATV is burning through oil, the more confident you can be this is your problem Most likely, it is one of the following

  • Bad seals.  Burning oil usually is a result of damaged or faulty seals.  The seals are designed to prevent oil from leaking into the valves where air and gasoline enter the engine’s cylinders, combust and power your ATV.  When the seals malfunction, oil gets in with the air and gasoline, leading to blue/gray smoke emitting your exhaust. Unless you know what you are doing, spend the few hundred dollars and have a mechanic handle this for you.
  • Bad oil.  Even if your seals are in decent condition, oil may get through if you are using bad oil.  API SG/JASO MA motorcycle/atv oils have additives that greatly increase the oil’s “film strength” (vs car oils) which helps to seal rings.
  • Bad spark plug.  This is an easy fix, but you want to make sure the piston rings aren’t bad too.  If the rings are bad, they will ruin the new spark plug in no time.
  • Worn or damaged piston rings.  Bad rings were discussed above in the timing section.  If you suspect this is the issue, you should run a compression test  First run the test dry and then wet. If the dry test produces higher readings, then your rings are probably worn.  You should replace the rings. To really be sure, you should replace the piston, hone it in, have the head milled as needed, and replace the valve seals and gaskets.  This will set you back a few hundred dollars, but it should vastly improve the health of your engine and get rid of the smoke if this is the source. You should also make sure to keep good, fresh oil in your quad, as old and dirty oil leads to friction that wears the rings more quickly.

If you think you have a ring problem and don’t want to go through with all the repairs, you may get lucky if the rings are just stuck rather than bad.  If you can free the stuck ring, you may just find your smoke problem fixed. Try some Marvel Mystery Oil and see if works.

Excessive clearance between the valve stem and the valve guide.  While this is more often associated with black smoke, it can lead to conditions where you have blue smoke.  Luckily, it is an easy fix.  Use a feeler gauge to check for the clearance level, and get it fixed if it is off.

Brent Huntley

Brent Huntley is the owner of ATV Man and is responsible for almost all the material on the website. He also runs photographyandtravel.com and loves to travel and ride ATVs with his family. When he isn't playing, his day job consists of owning Huntley Law.

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