Smoking Weed Wacker: 6 Causes and Fixes

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When it comes to a smoking weed wacker, there could be a few different causes. You can diagnose the issue by the color of the smoke. Weed eaters can produce smoke that is blue, black, or white. 

Some common reasons for smoking weed wackers are: improper fuel to oil mixture, exhaust buildup, engine not running at the proper temperature, and malfunctioning mechanical components. Most of these causes are easy to fix by draining the fuel and remixing the gas to oil ratio. 

We’re going to look at the different smoke emissions, what they mean, and how to fix it. By the time we’re done, you should easily self-diagnose and repair your smoking weed wacker. Let’s get wacky.

What Is a Weed Wacker?

Photo 15393494 | © Temistocle Lucarelli |

A weed wacker, technically labeled as a string trimmer, is a handheld lawn care device. This type of machine is used to trim weeds and areas of the yard that can’t be reached with a lawnmower. Weed wackers use a rotating string to cut grass instead of blades.

They usually have a two-stroke gas-powered engine. Adding gas into a weed eater isn’t the same as filling up your car. Two-stroke engines require you to premix gasoline and motor oil in the proper ratio, rather than adding gas and oil separately, as you do in a vehicle.

Some weed wackers can have a four-stroke engine, which does not require the oil and gas to be mixed together. These types of weed eaters produce less pollution. 

Mixing the oil and gas improperly is the most common cause of smoking weed wackers, and it’s usually a simple fix. But continuing to run the machine with the improper mixture can cause damage to your engine. 

Let’s look at some common smoking issues that you can experience with your weed wacker and how to fix them. 

Weed Wacker Emitting Blue Smoke

If your weed eater is putting out blue smoke emissions while running, it may be a sign that you’ve added too much oil to the gasoline. 

When the gas-to-oil mixture isn’t balanced, oil can get into the combustion chamber. As the oil burns, it pours out of the exhaust as blue smoke. You might also notice oil dripping out.

Continuing to run a weed eater with too much oil in the fuel mixture can lead to engine damage. You should immediately cut off the motor if you notice smoke that is turning blue. 

How to Fix

To fix a weed wacker that’s smoking blue, the first thing to do is turn the engine off. Next, you’ll need to drain the current mixture and refill with the proper oil to gas ratio. 

There are specific recommendations for different motor types, so check with the manufacturer for your exact needs. Most newer two-stroke models need a 50:1 ratio of gas to oil. Older models might require a 40:1 or 32:1 mixture. 

Be careful not to spill any of the mixtures on the ground while draining. Gas and oil can seep through the soil and contaminate the land and any nearby water. Plus, it’s illegal in most places. 

Weed Wacker Putting Off Black Smoke

A weed wacker that’s emitting thick black smoke can be a sign of a few different problems. Most of these issues can be resolved quickly without causing permanent damage to your motor.


If you’re noticing black smoke coming from your weed eater, the first thing to consider is your choke. The smoke could be a sign that you forgot to turn the choke entirely off after starting your engine.

If this is the case, the smoke should stop once you turn the choke off. Check to ensure there isn’t any smoke residue clogging the spark arrestor screen, which is located between the muffler and exhaust port, before continuing to use your weed eater.

Bad Gas

If you see black smoke and it’s the first time you’ve used your weed eater after a long time being put away, it’s most likely caused by old fuel. Drain your tank and refill with fresh, properly mixed fuel.

It’s best not to leave gasoline in a tank longer than thirty days, or you risk oxidation, which can corrode and clog your engine. The gas can also thicken, which will cause poor fuel economy (how much use you get per gallon). 

Poor Combustion

Poor combustion can also cause black smoke coming from your weed eater. In this case, the engine isn’t getting the proper balance of air and fuel, so it doesn’t run as hot as it’s supposed to. This causes the fuel to burn improperly, resulting in thick black smoke. 

To diagnose poor combustion, look for smoke residue buildup on the spark arrestor screen. You’ll need to clean this area to improve the air circulation so the fuel can burn off properly. 

Weed Wacker With Gray White Smoke

If your weed wacker is putting off gray-white smoke, you could be dealing with a significant issue. You must stop running the engine immediately upon noticing white smoke. Failure to do so can cause engine seizure. 

If you live in a higher altitude area, your problem could be something as simple as a malfunction with the automatically adjusting carburetor. If you’re lucky, making a simple adjustment to the carb with a screwdriver will fix it. 

Typically, white smoke is a sign that your engine isn’t getting enough lubrication, so it’s running hotter than it should. This issue is a result of not having enough oil in your fuel mixture. Or it could be that your gas has too much ethanol. 

How to Fix

To fix a problem with your gas, allow your engine to cool before draining the fuel. Then, replace with fresh gas, using an ethanol content of less than 10%. 

Always follow the manufacturer’s recommendations on proper gas to oil mixture. This will vary depending on whether you’re using a two-stroke or four-stroke engine and the engine’s age.

If you’re wary of mixing gas and oil, you can find appropriately portioned oil designed for two-stroke engines. All you do is add one bottle to one gallon of gasoline. Be sure you never use automotive oil in your weed eater, which can damage the motor. 

To achieve a 50:1 ratio of gas to oil, you would need one gallon of gas and a 2.6-ounce bottle of oil. For a 40:1 mixture, you’ll need one gallon of gas and 3.2 ounces of oil. 

You should also check the spark plug, which can become dirty or destroyed by a buildup of the smoke. Dirty spark plugs can lead to misfiring or weaker power. If you notice smoke deposits, clean or replace the plug.

Final Thoughts

Weed wackers are a great tool to keep weeds under control and hard to reach areas of your yard. But you do need to know how to mix gas and oil to ensure proper performance properly. Failure to provide the appropriate ratio can cause a smoking weed wacker that could end up causing damage to the motor. 

We’ve covered all the common reasons why a weed wacker would start smoking, including the different colored smokes and what they mean. We’ve also given you simple fixes that would rectify the situation so your weed wacker will resume its normal proper functioning. 

Remember that if your weed wacker is smoking, it’s best to fix the problem right away. Black smoke is typically not a sign of something severe; on the other hand, white smoke can be a severe problem.

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