7 Reasons Your Weed Eater Will Not Run at Full Throttle

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Does your weed eater stop running when you set it to maximum power? Everything looks fine at the start, but when you go full throttle it just halts. You are not the only one who has experienced this with a weed eater or string trimmer so without further ado, let us look into the reasons why this happens and the solutions.

A common reason why weed eaters die at full throttle is poor combustion due to lack of air. Also, if old fuel is left in the tank for a long time, it turns into a gel-like material and clogs the spark arrestor, carburetor and filters.

Choke is Left On

If your string trimmer is flooded or trying to cold start, you set the choke on. When the choke is activated, it minimizes air flow into the carburetor. The result is a rich fuel mix, and more fuel makes it easier for the engine to ignite.

After the engine starts you have to turn the choke off. If you do not, the engine will stop working because there is too much fuel and not enough air. Both 2 and 4 stroke string trimmers need a balanced air to fuel mix to work.

The solution is simple: remember to turn off the choke. You only have to set it on if the engine is flooded or you are starting it cold. Most people turn the choke on whenever the engine fails, and it is a good option. Just make sure to shut it off when your string trimmer is running.

Old Fuel

A high quality string trimmer is only as good as its power source. The Husqvarna 128LD is a versatile all-around string trimmer, but it needs fresh fuel to work.

Fuel loses its consistency when stored for long periods and not used. Eventually the fuel transforms into a gel-like material. This substance does not burn as well as regular fuel and clogs the engine.

When you set the trimmer to full throttle, it will require more fuel. If most of the gas has turned into gel, the engine will seize up.

If you are not going to use the trimmer for several weeks or months, drain all the fuel from the tank or add fuel stabilizer. This is the best way to prevent fuel from becoming unusable.

If the tank is filled with old fuel, remove it. Clean the tank, filters, carburetor and everywhere else the substance has spread. You have to get rid of it first otherwise it will clog the fresh fuel you put in. After the engine and tank are cleaned, you can pour fresh fuel.

Wrong Fuel

Weed eaters run on regular unleaded gas. The ethanol level must be no more than 10% and rated 87 octane. A two-stroke string trimmer requires a mixture of gas and oil, while 4-stroke engines store them separately.

The most common mistake made is using the wrong ratio. Two-stroke weed eaters use a 40:1 or 50:1 fuel ratio. If this is not followed, the engine might stall when you run it at full throttle. In some cases it might not start at all.

The other potential problem is using fuel with more than 10% ethanol. Too much ethanol is not good for small engines. As long as you meet the specs given here, your weed eater will run.

You might also be wondering what happens if you mix oil and gas in a four stroke string trimmer. At the very least, the machine will not work. The worst case scenario is it damages engine parts. The same thing can happen if you try to run a 2-stroke string trimmer without mixing fuel.

Adjust the Carburetor

The carburetor is where the air and fuel mixture happens. You can also adjust the engine speed if it is not running. If you are having problems getting the weed eater to work at full throttle, try adjusting the carburetor.

The following method works for most string trimmers including the PROYAMA 42.7cc Gas Weed Wacker. But do check your owner’s manual for the adjustment options available. In modern gas string trimmers you will see adjustment screws for idle speed and mixture. Follow these steps.

  1. Shut the string trimmer engine off.
  2. Remove the air filter cover and the air filter itself.
  3. You can see the carburetor now. Look for the idle screw. Check your manual if needed.
  4. Rotate the idle mix screw clockwise until the needle makes contact with the seat. Next, rotate the screw counterclockwise by one turn and a half.
  5. Test the string trimmer. If it does not run, turn the screw again. Keep adjusting and observing until the engine works.

Some string trimmers have a high speed adjustment screw. If you have one of these, use the following steps to adjust it.

  1. Let the weed eater run for a few minutes. If you can get it to half throttle that is even better. Shut the engine when it attains operating temperature.
  2. Rotate the high speed screw clockwise until it makes contact with the seat. Then rotate the screw one and one fourth or one and a half.
  3. Turn the engine on and set it to fast or high. Rotate the high speed clockwise until the engine starts slowing. Then rotate the screw the other way until the engine slows again. Bring the screw back to the middle.
  4. With the throttle idling, set it to fast. Your string trimmer should run now. Repeat the adjustments if it still will not run.

Replace the Fuel Filter

The fuel filter keeps foreign objects and particles out of the carburetor. It ensures the fuel is clean when it reaches the engine. Dirty fuel is bad for engines and a filter plays an important role in preventing this.

If the fuel filter is dirty or damaged, you can replace it. The following method works for most string trimmers, lawn mowers and other small engines.

  1. Look for the fuel filter. Usually it is inside the fuel tank. In other cases it is on the fuel line between the pump and the tank.
  2. If the filter is in the tank, drain the fuel first. If it is on the fuel line, take out the metal clips.
  3. Once you remove the filter, wipe it clean.
  4. Install a new fuel filter.

Related. 7 Reasons Weed Eaters Will Not Start (Solved))

Clogged Spark Arrestor

The spark arrestor is the small screen on the exhaust. It serves as a spark and fire prevention mechanism on most outdoor equipment. It is an important part of any string trimmer and needs to be well maintained.

Because a spark arrestor eliminates hot exhaust particles, it can get clogged. One symptom is your string trimmer cannot run in full throttle. It takes a while before a spark arrestor gets clogged but it does happen.

If you suspect this is the case, examine it closely. Remove the screen and wipe the dirt off. You might have to use soapy water to get rid of caked debris. Dry the screen and put it back on. Replace the spark arrestor if there is damage.

Clean the Air Filter

The air filter is located above the carburetor and keeps debris out of the engine. At some point the filter is going to get clogged by debris. When this happens, air can no longer get in the engine. As explained earlier, if there is not enough air, the fuel becomes too rich and will stall.

Cleaning and replacing air filters is easy. Remove the air filter cover and take the filter out. Check the filter. Replace the filter if there is a tear or it is just too grimy. If the filter is still whole, wash it with soap and water.

Once the filter is dry, put it back on. Reattach the cover and turn the string trimmer on.