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What Causes a Stihl Weed Trimmer to Smoke?

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If your Stihl weed trimmer starts to smoke, you should stop the engine immediately, because it could be caused by a problem that could do permanent damage. The problem is often more benign, but it’s better to err on the side of caution. Smoking can be caused by an overly rich fuel mixture or the presence of oil in the combustion chamber. On the more serious side, your engine may be seizing because it doesn’t have enough oil.

Poor Combustion

When the fuel/air mixture in the combustion chamber is too rich, the engine doesn’t run as hot as it should, and some of the fuel burns incompletely. This produces thick, black smoke that leaves deposits on the spark arrestor screen as the engine emits it. This can happen if you forget to completely turn off the choke after starting the engine, and it can also happen if the fuel is old. Stihl manufactures trimmers with two- and four-cycle engines, and both require a fuel/oil mixture. Both types of engines smoke if you add too much oil.

Getting Rid of Black Smoke

Improving combustion may be as simple as turning off the choke, but if you suspect a problem with the fuel, it’s best to drain it and refill the tank with fresh fuel mixed with the proper amount of oil. Stihl trimmer engines use a 50-to-1 fuel/oil mixture. If you aren’t sure how to mix the fuel, Stihl sells pre-mixed fuel in 1-quart cans. Be sure to clean the spark arrestor, which is a screen inserted between the muffler and exhaust port. If it’s dirty, it will continue to produce smoke even if the engine is running clean.

Grayish or White Smoke

Unlike black smoke, grayish or white smoke can be a sign of a serious problem. The engine produces it because it’s running too hot, and the reason is usually insufficient lubrication. Instead of putting too much oil in the gas, you may have put too little, or you may be using fuel that contains too much ethanol. If you stop the engine immediately when you see this type of smoke, you may be able to avert a catastrophic engine seizure, which isn’t repairable. Let the engine cool and change the fuel, using fuel with no more than 10 percent ethanol and adding the proper amount of oil.

Tune-Up the Trimmer

Stihl trimmers come from the factory with a standard carburetor setting that optimizes the fuel/air ratio. This setting may cause the engine to smoke at higher altitudes, because the air pressure is lower and the fuel mixture therefore richer. You can make the mixture leaner by adjusting the carburetor with a screwdriver. Another simple tune-up procedure that should reduce the output of black smoke is to clean or replace the spark plug. The plug electrodes are probably coated with soot, which can cause it to misfire or produce a weaker spark, both of which adversely affect combustion.

What Causes a Stihl Weed Trimmer to Smoke?. If your Stihl weed trimmer starts to smoke, you should stop the engine immediately, because it could be caused by a problem that could do permanent damage. The problem is often more benign, but it’s better to err on the side of caution. Smoking can be caused by an overly …

My weed wacker is smoking. is it because i put to much gas or to much oil?

I know I put more gas in the tank. I did use 2 stroke oil but I am not sure of the ratio. Please help.

The engine seemed to be stressed.

6 Answers

If the smoke is coming out through the muffler, you added too much oil. If it’s coming off the engine, you may have spilled oil on the motor, and it’s burning it off.

Check the manual, or the plaque on the engine, or the dealer’s website. My weed whacker uses fuel mixed at either 32-1 or 40-1. I don’t know for sure, but I marked it on the cap. The leaf blower or snowblower use the other mix. So I have 2 gas cans, with separate mixtures, and the amount of oil to use per gallon clearly written on them. You may want to do the same. If you can’t find it for sure, then use 32-1. A richer mix will smoke a bit more, but it will lubricate the engine. And a little too much oil will just foul the plugs – which is probably why yours sounds stressed, I think. Too little may cause the engine to burn itself up.

If the smoke is white the carburetor is letting too much gas flow and it needs adjustment, but if the smoke is blue then you put too much oil in the gas. If that is the case then drain the gas from the weedeater, buy a small bottle of 2 stroke oil that has a 40:1 ratio and mix with 1 gallon of fresh gas, fill the weedeater and start it. it might take a while for it to stop smoking. If you read the bottle it will have all the info you need.

if the smoke is blue to much oil

SOUNDS LIKE THERE IS TOO MUCH OIL IN THE GAS.

I know I put more gas in the tank…I did use 2 stroke oil but I am not sure of the ratio. Please help. The engine seemed to be stressed.