White smoke from the tailpipe looks serious, but usually, it’s a simple problem, easily fixed.
Top 4 reasons for white smoke from an air-cooled ATV include:
- Too much oil
- Wrong oil type
- Contaminated gas
By the end of this post, you’ll understand the root causes of white smoke from an air-cooled ATV and what you can do to fix them.
1 Too Much Oil
Mixing gas and oil is mission-critical to a two-stroke engine. As you know, a two-stroke doesn’t have a sump filled with oil; instead, the engine depends on the two-cycle oil to lubricate and cool the moving parts.
Without the oil, the engine would seize solid within minutes. Too little oil in the gas mix risks seizure also. Being over-generous with the oil is bad too. It causes the motor to run lean, and a lean engine runs fast and hot.
In addition, excess oil accumulates in the crankcase and is eventually burnt in the combustion chamber, where it causes a ton of white smoke. If your bike is a two-stroke, its carburetor is calibrated (jetted) to burn oil and fuel to a specified ratio, for example, 32:1. Deviating from this very precise ratio can cause your engine to run lean or rich. Both will shorten the life of your engine.
If your bike is a four-stroke simply overfilling with oil is the more usual cause of white smoke and is easily fixed, drain off the excess oil. Most single cylinder ATVs will take approx. 2.5 US qts of oil.
2 Wrong Oil Type
Using the wrong type of oil is a common mistake. Regular engine oil is too heavy for burning in a two-stroke engine and will produce plooms of white smoke. Engine oil won’t protect your engine either. It doesn’t thoroughly mix with gas, and your engine will be damaged by friction and heat. Even a short period of operation could cause damage.
Using the wrong grade oil in a four-stroke engine may cause some bikes issues. Running a bike on a very light fully synthetic may cause excessive oil consumption. Best to check your owner manual for the oil type recommended, despite what lots of folks say all oil is not the same.
You will need to be mindful of operating in extreme temperatures.
If you live and play in sub-zero temps, you may need to use thinner oil which as you know flows more easily in cold temps. See chart.
Common oil grades include – 5W30, 10W30, 10W40, 15W40, 20W40, 20W50.
3 Contaminated Gas
Bad gas will cause any engine to act up. Regular gas goes stale after three months and blended behind to go off in as little as one month under certain conditions.
Fuels with higher alcohol content generally aren’t good for two-stroke engines. Ethanol blended fuels like E15 burn hotter, and heat is the enemy of any motor. 87 octane regular gas is preferred.
Blended gas is bad open to atmosphere fuel systems and a gas stabilizer should be used to help keep the gas fresh and to protect the fuel system from gumming, a common winter storage issue.
You’ll find the gas stabilizer I recommend here on the ATV parts page.
Riding through water will cause steam on the exhaust, and if the airbox gets a drink, the engine will ingest it and turn it into steam. So, if you’ve been playing in the water, check that airbox, its drain, and air filter.
Drain the carburetor gas bowl too.
Accidentally and unknowingly filling the gas tank with diesel, white spirits, thinners, or I’ve even had to drain wine/vinegar from a gas tank. Accidents happen, especially when gas refill cans aren’t clearly marked.
If you suspect gas contamination, you’ll need to drain the tank, carburetor bowl, and fit a new inline filter.
Those from a warmer climate may not be familiar with white smoke at startup. It’s part of motoring life in colder climates. The exhaust pipe gases create condensation as it meets the cold ambient air. As the engine warms up, the white smoke increases in opacity and reduces in quantity.
If this sounds like your symptom, you’ve got nothing to worry about.
Other Possible Causes
Here’s a list of other possible causes of white smoke in a four-stroke motor, some are serious, and some and relatively easy to fix.
Oil stem valve seals – These oil seals live at the top of the engine on the valve stem. They allow for cylinder head lubrication, however, when they age they become brittle and allow oil to sneak into the engine, especially noticeable by increased smoke on initial startup.
Cylinder head gasket – graphite material between the engine block and cylinder head. Its job is to seal the combustion chamber and help keep crankcase oil separate from the combustion chamber.
Worn cylinder rings – Worn rings are possible too. This does require an engine strip down to fix and while in there it usually makes sense to take care of a few other jobs like vale reseating, oil stem vale seals, head gasket, etc.
A leak-down test is excellent at detecting a cylinder compression issue.
You’ll find the tools I recommend including head gasket test kit here on the ATV tools page and you’ll find common spare parts here on the ATV parts page.
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John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.