Weed Eater Won t Start: 6 Causes and Steps To Troubleshoot

Weed eaters are mostly powered by 2-cycle engines. And like every other machine, they develop issues after being used for a while. While some of them might be unfixable and require replacement, the majority of these issues can be resolved, sometimes even without professional help. In this article, we cover the various reasons why a weed eater won t start and how to resolve the issue.

Weed Eater Won t Start: Causes Of A Stalling Weed Eater

The engine of a weed eater is made up of several parts. A problem with some or a combination of these parts could cause the weed eater to cut off after turning it on. Below is a list of issues that could cause an engine to stall:  

1. Fuel problems
2. Faulty choke
3. Clogged fuel filter
4. Dirty air filter
5. Clogged exhaust screen
6. Carburetor issues

Now, let’s dive into each of these issues and show you how to resolve them.

1. Fuel Problems

There are two issues in this section that could cause a weed eater to stall;  the fuel level, and the fuel mixture.

Fuel Level

The weed eater stalls whenever the fuel in it is insufficient. Ensure that it has enough fuel to start and keep it running for the duration of your use. Also, whenever filling up the tank, make sure the fuel doesn’t go past the designated line to allow room for air in the tank. After topping up the tank, depress the primer bulb to prime the fuel system and make sure it’s filling up. 

Fuel Mixture

A 2-cycle engine is fueled by a precise mixture of gas and oil. The oil in the fuel lubricates the engine while running and prevents it from overheating. An incorrect fuel mixture or bad fuel can cause the weed eater to stall when started. When fuel is left in the weed eater for a long time, some of the gas evaporates leaving sludge behind that soon blocks the carburetor fuel intake port, thereby causing the engine to stall. 

To prevent this, ensure you empty your fuel tank before storing long term, or add a fuel stabilizer to increase the fuel’s shelf life and prevent it from going bad quickly. As for incorrect fuel mixtures, when it has too much oil, the engine smokes when run. Too little and it overheats. Both scenarios can cause your engine problems over time.

Another thing that can affect the quality of your fuel is the ethanol content. While it is acceptable to use a fuel mixture with up to 10% ethanol, it is better to avoid it completely. Ethanol, if left for a while, collects water, causing the mixture to separate into a gas layer and an ethanol-water layer. Also, ethanol doesn’t bond with the oil in the mixture, unlike with gas, leading to poor lubrication in the engine. 

Using commercial premixed fuels eliminates all these issues. Commercial premixed fuels are ethanol-free, have longer shelf lives, have the correct level of fuel stabilizers, and have a very precise gas-oil ratio. This makes them safer than their DIY counterparts, and they do not leave residue in the tank or engine. They are more expensive than homemade premixes though. 

If you’d rather do it yourself or can’t afford the commercial premixes, here are some of the things to note. 

• Use ethanol-free fuel for your mixture. 
• Use a synthetic or semi-synthetic oil for the mix.
• The Gas-oil ratio for most modern weed eaters is 50:1. A 40:1 mix is also acceptable. Most hand-held weed eaters work on a 40:1 mix.
• If your equipment is older(before 2002), your gas-oil mix should be 32:1. 
• To ensure a perfect mix, make use of cans with standard volumes such as a 5 liter (5000ml) or 20 liters(20,000ml) can.
• Add the measured oil to the can you are using for the mix before pouring the measured gas into it. Doing it this way mixes the oil with the gas for you. Alternatively, you can pour the oil into the measured fuel and shake the can to mix it.

2. Faulty Choke

The choke restricts the flow of air into the carburetor bringing about an enriched fuel-air mixture in the carburetor. This is necessary when cold starting the weed eater. When starting a weed eater, the choke is moved to the farthest position. The moment the engine comes on, it is returned to its rest position. 

If your choke is permanently stuck at the on position, the engine would start successfully, but then stall after some seconds as it’s no longer getting enough air. If, on the other hand, the choke is loose, vibrations from the engine might move it from the rest position to the on position or halfway, causing the engine to either stall or smoke due to incomplete combustion of the fuel-air mixture. To resolve this, replace the choke with a new one. This video explains how to go about that. 

3. Clogged Fuel Filter

The fuel filter is there to prevent debris and other foreign particles from getting into the fuel line. If you’ve been using bad fuel mixtures, there is a good chance that your fuel filter is now clogged. This reduces the amount of fuel going into the carburetor. The fuel that gets in might be enough to start the weed eater and even keep it idle. But once it’s throttled, the weed eater won t start. 

You have to clean or replace the fuel filter, before turning it on again. It’s better to just buy a new filter though as they are inexpensive. You might not be able to completely clean the filter if you go that route. To replace the fuel filter:

1. Drain the fuel tank into a clean gas can.
2. Get a piece of tire wire(or something similar) and make a hook at one end.
3. Remove the fuel cap and dip the tire wire into the fuel tank. 
4. Get the hook under the fuel line and make sure you don’t puncture it.
5. Pull up the fuel line with the tire wire till you can see the filter. You should now be able to pull out the fuel line with your hand.
6. Hold the end of the fuel line tightly and pull out the fuel filter. Make sure the fuel line doesn’t slip from your hand. 
7. Insert the filter replacement into the end of the fuel line.
8. Put the fuel filter back in and make sure it goes to the bottom. 
9. Pour back the fuel and cover the tank.

4. Dirty Air Filter

In the carburetor of a weed eater, fuel is mixed with air before being sent to the engine to ensure complete combustion of the fuel. Like the fuel, the air going into the carburetor is filtered for particles with an air filter. Should the air filter get too clogged, the engine either begins to sputter and cuts off or it smokes when running, just like when you have a bad choke. 

To clean your air filter when clogged, follow the following steps.

1. Turn on the choke to prevent dust and other particles from entering the carburetor. 
2. Unscrew the filter cover and take out the filter element. 
3. Brush the filter element to remove the dust on the surface. 
4. Dip into warm, soapy water for a few minutes.
5. Clean the inside of the filter cover using compressed air.
6. Use an engine degreaser/cleaner to clean the area around the carburetor
7. Take out the filter element and let it dry naturally, then replace and cover with the filter cover.

5. Clogged Exhaust Screen

Another part of the weed eater that can get clogged is the exhaust. The primary function of an exhaust is to take out waste gas from the engine of the weed eater. This is to ensure that the engine operates in a smoke-free environment. At the mouth of the exhaust is a spark arrestor screen. The spark arrestor screen is a steel mesh that prevents large combustible particles from flying out of the engine. 

When a weed eater is used with a fuel mixture that has too much oil, it causes the engine to smoke. Over time, the smoke clogs the spark arrestor screen preventing it from properly letting out waste smoke from the engine. This causes the engine not to function properly, or stall. A faulty choke also causes the engine to smoke due to incomplete combustion and could block the spark arrestor screen as well. 

Cleaning or replacing a spark arrestor isn’t as easy as an air or fuel filter. To clean the spark arrestor you would need a propane torch and a plier. 

1. Unscrew the plastic muffler guard.
2. Unscrew the exhaust port cover. You should now be able to see the spark arrestor.
3. Take out the spark arrestor and hold it with a plier.
4. Light the propane torch and use it to clean the spark arrestor by directing the flame continuously at it. 
5. Do this till you can see through the spark arrestor.
6. Wait for it to cool down then place it back in its position.
7. Screw on the exhaust port cover and the muffler guard.

6. Carburetor Issues

If you’ve tried all the above steps and your weed eater won t star, then it’s time you looked into the carburetor. The carburetor determines the appropriate fuel-air ratio necessary for combustion in the engine. It also regulates the idle and full throttle speed of the weed eater. There are four things in a carburetor that could cause a weed eater to stall; the fuel mixture regulators(idle and full throttle), clogged carburetor, worn out fuel pump diaphragm, and rigid/worn out metering diaphragm.

The Fuel Mixture Regulators

The fuel mixture regulators are two screws usually located behind the air filter. They are used to control the engine speed by regulating the supply of fuel to the engine when it’s idling and when it is fully throttled. If the engine cuts off while idling or fully throttled, and you have tried the preceding steps, try adjusting the fuel mixture regulators. 

The screws used to adjust the fuel mixture being supplied are labeled ‘L’ or ‘Lo’ to adjust the idle speed, and ‘H’ or ‘Hi’ to adjust the speed at full throttle. To adjust the ‘H’ screw: 

1. Start the weed eater and rev it fully by holding the throttle down. 
2. Turn the screw clockwise till the engine speed is at its fastest.
3. Now turn the screw counterclockwise till the engine speed begins to drop
4. Then turn the screw counterclockwise till the engine speed just begins to rise. Leave it there.

For the ‘L’ screw:

1. Start the weed eater, but leave it idling this time.
2. Turn the screw counterclockwise till the engine is idling at its fastest.
3. Now turn it counterclockwise till the engine speed begins to drop. Leave it there.

NB: If you are unable to locate the screws, consult your manual, or go online and search for the location of the screws for your brand. 

Clogged carburetor

If you have been running your engine on bad fuel, it is likely to have clogged your carburetor. You can clean this by spraying the carburetor with a degreaser after taking it apart to get rid of all the sludge and dirt in it. This video does a good job of explaining this process. If after doing this, the engine still stalls, move on to the next step.

Fuel Pump Diaphragm

The fuel pump diaphragm helps regulate the fuel in the fuel-air mixture. It is a piece of plastic with two free-moving flaps facing inward. If the diaphragm gets deformed or worn out, it would need to be replaced. 

Metering Diaphragm

The metering diaphragm also controls the fuel going into the engine. It has a cotton-like texture and it’s supposed to be flexible. If the metering diaphragm is rigid, it would be unable to perform its function properly and therefore need to be replaced.  

This article shows how to replace both the fuel pump diaphragm and the metering diaphragm. 

Maintenance Tips

There are a bunch of things that would make it hard for a weed eater to stay running and they can all be easily prevented. If your weed eater fails on you, any of the above-listed steps should be followed but to generally maintain and increase the lifespan of your gardening tool, you should:

• Clean the weed eater with a damp towel after use to prevent rust or buildup of dirt.
• Before storing for a long time, empty the tank of fuel to prevent it from going bad and clogging the carburetor.
• If you are going to store the weed eater with fuel in it, make sure it’s ethanol-free and contains a fuel stabilizer. 
• Take note of the following as well before storing at the end of each season:
  • Ensure the air and fuel filters are free of impurities. 
  • Make sure the carburetor works fine.
  • Check the exhaust and make sure it isn’t clogged.
• Finally, if you’re going to premix your fuel, make sure to renew it monthly.