Having a weed eater that bogs down when you try to increase the throttle can be a real pain and can make weed-eating the yard a long, slow process. Now you’re not alone if your weed eater bogs down, as this has happened to me on several occasions over the years, as it will with most people who own a weed eater. So, what’s going on, and why is this happening? Well, let me go over some of the common causes and explain what the problem could be.
Weed Eater that Bogs Down (The Short Explanation)
There are several reasons why a weed eater bogs down and is unable to maintain high RPMs and full power. Here are 8 common reasons why your weed wacker might be bogging down.
- Wrong Fuel Mix
- Clogged Fuel Filter
- Split Fuel Line
- Leaking Gas Cap
- Fouled Spark Plug
- Clogged Exhaust
- Blocked Air Filter
- Dirty or Damaged Carburetor
8 Possible Reasons Why Your Weed Eater is Bogging Down
As you can see, there is a pretty long list of potential issues that could be causing your weed eater to bog down. So, let’s dig into the list and see what’s going on. I’m pretty sure that one of these issues will be why your weed eater struggles and loses power.
Wrong Fuel Mix
Typically a weed eater will have a 50:1 fuel-to-oil mixture. If you don’t get your weed eater fuel mixture right, then fuel combustion won’t happen as intended, resulting in a series of different problems. Having too much oil in your mix leads to symptoms such as additional smoke, poor performance, and excessive carbon deposits. So when you increase the throttle, the fuel mix can not burn efficiently, and you feel a loss of power, otherwise known as bogging down.
On the other hand, having too little oil in your mix isn’t going to really bog down your weed eater, but it will quickly damage your weed eater’s engine. So, getting your weed eater fuel mix right is important for more than just preventing your weed eater from bogging down.
Clogged Fuel Filter
The fuel filter is responsible for filtering out fuel imperfections and debris from the fuel in your weed-eaters gas tank. Therefore, the fuel filter becomes clogged as time goes on, and the fuel flow rate reduces. So, as you increase the throttle on your weed eater, there is a greater demand for fuel.
Now, if your fuel filter is clogged, the engine is not going to be able to receive the fuel it needs, and it will bog down or you may see that the weed eater dies when you give it gas. The simple fix for this issue is to replace the weed eater’s fuel filter.
Split Fuel Line
Another reason your weed eater bogs down could be a split in the fuel lines. If you take a close look at the line coming from your weed eater’s fuel tank, you’ll find one fuel line that draws fuel from the tank and one that returns the fuel back to the tank. Now, if the outflow fuel line is punctured in any way, then it will not have the ability to suck in air which will, in turn, alter the air/fuel mixture.
In my experience, a small puncture in the outflow fuel line won’t really be much of a problem on low RPMs as the fuel isn’t moving very fast at all, and there isn’t a great demand. However, when you increase the throttle, the fuel flow increases, and air has a much greater ability to get drawn in through the puncture.
The second fuel pipe is designed to create pressure in the fuel tank so that fuel can be forced into the carburetor. If there is a puncture in this fuel line, there won’t be any tank pressure, or at least there won’t be enough. So, if you notice any damage to either of the fuel lines, you’ll want to install replacements.
Leaking Gas Cap
To maintain pressure in your weed eater’s fuel tank, your weed eater is fitted with a gas cap with an o-ring/gasket. If this o-ring/gasket on the gas cap is damaged or missing, air will escape, and again, pressure will not force fuel to the carburetor.
So, if you run your weed eater for a minute or two, pressure should build up in the tank, which you can release by removing the gas cap. If you can’t hear the air escape once you remove the cap or fuel leaks from the gas cap, you’ll know that you don’t have a good seal, which could cause your weed eater to bog down.
Fouled Spark Plug
A number of reasons can cause an issue with your weed eaters’ spark plug. For example, you can notice issues like an old burned-out spark plug, a sooted-up spark plug from too much oil in the fuel mix, and a spark plug that can’t ignite fuel because the weed eater is not getting a spark and a flooded carburetor.
Now these issues can vary depending on the specific conditions. A fouled spark plug could be the reason why your weed eater is fine one minute and then starts to struggle all of a sudden. The easiest way to check is to remove the spark plug and inspect its condition.
Clogged Exhaust
One thing that tends to get overlooked when it comes to a bogged-down weed eater is the spark arrestor in the exhaust pipe. Why is this? Well, probably because not many people know they even exist. So what is a spark arrestor? Well, it’s a small mesh attached to the exhaust pipe. Exhaust gases have to pass through the spark arrestor before they exit the muffler. The spark arrestor’s main job is to extinguish any sparks from the engine before they have a chance of hitting the ground and potentially causing a fire.
After a while, all of the carbon from the combustion process and any unburned oil passing through the spark arrestor begin to clog the mesh. When this happens, your weed eater cannot expel the exhaust, which will bog it down. So, you will either need to clean or replace the spark arrestor to restore the airflow through your weed whacker’s engine.
Blocked Air Filter
Next on the list of potential reasons for a bogged-down weed eater is a blocked air filter. Similar to the effects of having a blocked spark arrestor, a blocked air filter will also disrupt the airflow in the engine and reduce your string trimmer’s ability to properly operate.
So, as you increase the throttle on your string trimmer, there is an increased need for air in the carburetor to mix with the fuel. So if your air filter is clogged, the air will not enter the carburetor, reducing combustion. When you have significant build-up on your air filter, you’ll likely start to notice your weed eater starts then dies very quickly, or just won’t start at all.
So, all you need to do is remove and inspect the air filter. Typically, you will find that the air filter is either blocked with debris or oil. Therefore you’ll need to see if you can clean the air filter or if it needs to be replaced.
Dirty or Damaged Carburetor
Finally, the carburetor on your weed wacker can suffer a number of different issues that can all lead to your weed eater bogging down (it can also be responsible for issues like a weed eater that will only run with the choke on). This can happen in different ways, such as a dirty carburetor blocked with fuel residue and debris to components failing. What this does is prevent the fuel and air from mixing correctly, block the fuel, or allow air into the carburetor when it shouldn’t.
There are a few ways you can approach repairing our weed-whackers carburetor. You can clean the carburetor, install a carburetor service kit, or completely replace the carburetor. Now depending on your confidence with fixing small engines, you may just opt for replacing the carburetor. Now this isn’t the cheapest option, but it will eliminate any carburetor issues.
How to Fix a Weed Wacker that Bogs Down (8 Possible Solutions)
Now let’s take a look at the different fixes to stop your weed eater from bogging down. I’ve included all the steps and tools that you will need for each repair, so you should be back up and running in no time at all.
Using the Right Fuel Mixture
Getting the right fuel mixture is just a case of knowing what the correct mix should be and being as accurate as possible when it comes to mixing. First, you’ll want to confirm the mixture you should be using in your user manual. Typically, most new or recent weed eaters use a 50:1 mix.
Therefore, you could opt for using a premix product such as a Stihl Moto Mix 50:1 2-cycle fuel mix, or you can mix the fuel/oil yourself. Now the easiest way to mix your own fuel is to use an oil container that matches the size of your gas can.
For example, if you have a 2.5-gallon gas can, you can use an oil like a Stihl 6.4 fl oz 2-cycle oil. Using oil containers that are specific to the size of your gas will eliminate any need to measure out the oil and will avoid ratio mistakes.
Finally, you can use a measuring container to measure out the volume of oil accurately and add it to your can, followed by adding the fuel. Now this method is more prone to mistakes, but if you take your time and know your ratios and volumes, you will be fine.
Replacing a Fuel Filter
To replace a weed eater fuel filter, you’ll need first to remove the filter from the fuel tank while it’s attached to the fuel line. Once you have it out of the tank, you can carefully pull the fuel line from the filter. Then attach your new fuel filter to the fuel line. Finally, drop the new filter into the fuel tank, and you are done. This quick and easy fix can make a world of difference.
Tools & Parts to Replace a Fuel Filter
- Small Hook
- Replacement Fuel Filter
Replacing Fuel Lines
Fuel line setups on weed eaters vary from manufacturer to manufacturer, so there isn’t one repair that suits every model. Therefore, in my example, I’ll use a Stilh FS-90. Now, the FS-90 has two small fuel lines connected between the fuel tank and the carburetor. So, all you need to do is remove the old lines and install new ones.
All you have to do to replace the fuel lines is push them into place, so you won’t need any special tools. You just need the right size and length of replacement fuel lines. So, pull the old fuel lines off of your weed eater and replace them with your new lines. Just make sure that you attach the new lines in the right order.
Whenever I make this repair, I replace one line at a time so that I don’t get the connections mixed up.
Tools & Parts to Replace a Fuel Lines
- Replacement Fuel Line
Replacing a Fuel Cap
Again this is a super simple repair, and you don’t need anything special. All you need is a replacement gas cap. So, unscrew the old gas cap and screw on a new one. Because gas caps aren’t universal, you need to make sure that you get the right replacement cap for your string trimmer. If you don’t and try to use the wrong gas cap, you could run into the same problems you are trying to avoid.
Tools & Parts to Replace a Gas Cap
- Replacement Gas Cap (Weed Eater Specific)
Replacing a Spark Plug
When it comes to replacing a spark plug, the most important thing is to make sure that you use the right replacement plug. Even though lots of spark plugs are the same size and thread, they are actually very different. So, either check your user manual or take a look at the reference on the side of the existing spark plug.
Once you have the replacement spark plug in hand, remove the old plug and install the replacement using a spark plug wrench. Also, be careful not to over-tighten the new spark plug, as they are pretty delicate. The last thing you want to do is snap the new spark plug in half.
Tools & Parts to Replace a Spark Plug
- Replacement Spark Plug (Engine Specific)
- Plug Wrench
Replacing a Spark Arrestor
Now spark arrestors come in all shapes and sizes and can differ between brands and models. Some are flat pieces of mesh that screw to the side of a muffler, and some are like a spark plug, as in you screw them into the muffler.
So, all you need to do is remove the old spark arrestor and install a new one. You may need to use a screwdriver or a socket wrench to remove the old arrestor and secure the replacement. Typically this is a very simple repair that you can complete in just a few minutes as long as you have the right tools and replacement parts.
Tools & Parts to Replace a Spark Arrestor
- Replacement Spark Arrestor (Weed Easter Specific)
- Screwdriver
- Socket Wrench
Replacing an Air Filter
So if you have already inspected your weed eater’s air filter, you will have removed the air filter cover and the actual air filter. Now, if you need to install a replacement, all you have to do is install a new filter and place the air filter cover back on.
Now the only extra step I would add is to wipe off any oil residue inside the air filter housing. This will prevent your new air filter from getting contaminated from day one. Again this is a repair that should only take a few minutes and should only cost a couple of bucks.
Tools & Parts to Replace a Weed Eater Air Filter
- Replacement Air Filter (Engine specific)
- Screwdriver
- Shop Rag
Replacing a Weed Eater Carburetor
If you choose to go the route of completely replacing your weed eater’s carburetor, then this is going to be a more lengthy process. But as long as you take your time, you should be fine. So, here are the steps you will need to follow to install a new weed eater carburetor successfully.
- Disconnect the cable from the spark plug
- Drain the fuel tank
- Disconnect the fuel lines from the carburetor
- Remove the air filter cover
- Remove the air filter
- Remove the screws attaching the air filter housing and carburetor to the engine
- Lift the air filter housing and carburetor off of the weed eater
- Disconnect the throttle cable from the carburetor
- Connect the new carburetor to the throttle cable
- Place the new carburetor onto the engine, including all the required gaskets
- Place the air filter housing onto the carburetor
- Install the mounting screws
- Connect the fuel lines
- Connect the spark plug
- Fill the tank with gas
Tools & Parts to Install a New Weed Eater Carburetor
- Replacement Carburetor (Engine Specific)
- Screwdriver
- Socket Wrench Set
- Needle Nose Pliers
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