How to Unflood a String Trimmer

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It's easy to unflood a string trimmer.
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Before a string trimmer will start, gas has to be supplied to the carburetor, and manufacturers provide one of two ways to do this. The most common is a choke, which is a lever that partially closes the carburetor to provide a richer fuel mixture than the engine needs while it's running. The other way is a priming bubble, which squirts fuel directly into the carburetor each time you press it.

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If your string trimmer has a weak spark or the fuel is old, it may not start when you pull the cord the first few times, and it's tempting to keep the choke on or continue pushing the priming bulb until the carburetor has too much fuel. When you flood the engine this way, the spark plug can get partially immersed in fuel and fail to spark. There's an easy way out of this dilemma.

How to Unflood a String Trimmer

If you flood your car's engine, you often have no recourse but to wait 10 or 20 minutes for the gas to drain from the carburetor before the engine will start, but that isn't necessary with a string trimmer. A simple procedure should get the engine going without any delay at all.

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Step 1: Open the Choke

Set the choke to the "off" position. On some models, this position is labeled "run," or it may be denoted by a single vertical line as opposed to two vertical lines for the "choke" position. If your model has a priming bulb, you don't have to worry about the choke but just remember not to press the priming bulb.

Step 2: Hold In the Throttle

Depress the throttle all the way as if you were operating the trimmer at full speed.

Step 3: Quickly Pull the Cord Several Times

Continue holding in the throttle while you pull the starting cord repeatedly several times. Eventually, the motor will sputter, and if you keep pulling, it will eventually turn over. When it does, ease off the throttle until the engine is running smoothly.

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Why This Works

When you open the choke and depress the throttle, the engine will draw a small amount of gas from the carburetor and combustion chamber each time you pull the cord. While this gas doesn't get burned, it does get expelled through the exhaust. Eventually, the ratio of gas to air in the carburetor becomes lean enough for the spark to ignite it.

To make this process even faster, you can increase the air circulation in the carburetor by removing the air filter. Just remember to replace it as soon as the engine turns over, and the trimmer is operating normally.

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Keep Your Trimmer in Shape

If you're experiencing frequent problems starting your trimmer, simple maintenance can get it back in shape:

  • Replace the spark plug.​ Spark plugs eventually corrode, or the terminals get covered with carbon. You can clean a spark plug, but plugs are inexpensive, so it's better to replace it.
  • Clean or replace the air filter.​ Filters are also inexpensive and easy to replace, but giving your air filter a good cleaning with soap and water also usually does the trick.
  • Adjust the carburetor.​ Follow the manufacturer's instructions for adjusting the carburetor screws, particularly the idle and low speed adjustment screws.

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Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker.com.