Gasoline-powered grass trimmer emitting smoke or smelling of gasoline: causes and quick fixes

The exhaust from a gasoline-powered grass trimmer is normally colorless. If blue-white or black smoke is coming out, be careful because this indicates a problem with the engine. Always refer to your grass trimmer’s user and maintenance manual; that said, in this article we’ll explain what this means and provide general guidance on how to fix it.

Why is the grass trimmer emitting white smoke?

Blue-white smoke from a grass trimmer usually indicates that oil is burning in the engine. Oil in an internal combustion engine is essential for minimizing friction between mechanical components and dissipating heat. But when does the oil burn, causing the grass trimmer to emit blue-white smoke? Here are some common scenarios:

• The grass trimmer is operating on very steep terrain.

• The grass trimmer (and therefore the engine) has been turned upside down or tilted incorrectly, for example when changing the oil or during winter storage.

• The oil reservoir is too full.

• The engine oil is not suitable.

• The engine cylinder or piston rings are worn or damaged.

• The head gasket is damaged.

Do not use the grass trimmer on slopes that are too steep: the user manual usually specifies the maximum slope angle at which you can operate it. Also, be careful how you handle the grass trimmer during maintenance, such as which way you tilt it. In the tool shed, store it so that the engine is horizontal to prevent oil or gasoline from spilling. This is always a good practice, even during extended periods of inactivity, such as winter storage. In fact, before storing the trimmer, we recommend that you drain the fuel tank and the carburetor.

With the grass trimmer on a level surface and the engine turned off and cool, check the dipstick to see if the engine oil level exceeds the maximum mark. If the level is too high, partially drain the reservoir by following the oil change instructions for your grass trimmer; for example, you could use a syringe to remove the excess oil. In addition to causing smoke, excess engine oil can dirty the spark plug: take this opportunity to check both, clean the spark plug, and replace the filter.

For specifications on the engine oil to use, consult your grass trimmer’s user manual. The same applies to knowing the steps to follow to change it properly. If you have an Efco gas-powered grass trimmer, we recommend using automotive detergent oil for 4-stroke engines, with an API Service classification of SG, SH, or higher. Generally, an oil with a viscosity grade of SAE 10W-30, such as SAE 30 oil for 4-stroke engines, is suitable for all seasons. However, if winter temperatures in your area drop well below freezing, an SAE 5W-30 viscosity grade might be more suitable.

If the engine oil is the correct type and the oil level in the reservoir is normal, the problem may involve engine components that—due to wear or damage—are allowing oil to leak into the combustion chamber. In this case, we recommend that you contact your trusted Efco service center to prevent more serious damage, such as the engine seizing up.

Why is my grass trimmer emitting black smoke?

Instead of white smoke, your grass trimmer may be emitting black smoke. This usually happens when there are carburetion issues, causing the engine to burn more fuel than air. This can occur, for example, if the air filter is very dirty or damaged, or if the carburetor needs to be adjusted.

Clean the air filter according to the instructions in the user manual, for example, by simply blowing it out with compressed air or cleaning it with a special concentrated degreaser, then rinsing and drying it with compressed air. If the filter is very dirty or damaged, replace it immediately.

To adjust the amount of fuel entering the engine’s combustion chamber, contact the technicians at your nearest Efco service center, who are also available to answer any questions or concerns you may have.

Speaking of spark plugs—which are the heart of the grass trimmer’s ignition system, as well as that of any gasoline-powered gardening tool—here’s an article on spark plug maintenance. Here, you can learn more about how the quality of oil and gasoline affects the health of your 2-stroke engine.