5 Things to Check if Your Weed Eater Isn’t Running Correctly

We’ve all been there—pulling and pulling on the string of the weed eater, only to be greeted with nothing but confusion and frustration. If your weed eater isn't starting or running correctly, there are five common culprits often causing the issue.

Below, we will walk you through the five things you need to check, and potentially save you a trip to the repair shop.

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1. Spark Plug

Shop Spark Plugs

Starting with the most common and easiest fix: the spark plug. Small engines like those on weed eaters depend heavily on the spark plug to ignite the fuel. Over time, the spark plug can become dirty or worn out, leading to problems starting the machine.

Use a spark plug wrench to remove the plug from the engine. Once removed, examine the tip closely—if you see corrosion or soot buildup, you've likely found the problem. To fix this, simply install a fresh spark plug which are inexpensive and can be found at any hardware store, your local John Deere dealer, or using the link above. They’re typically marked on the side with the correct type for your machine, so be sure to carefully read the instruction manual for your machine to locate the type you need. To install, screw in the new plug, tighten it up, replace the cap, and give your weed eater another try.

2. Carburetor Adjustment

If the spark plug checks out and the weed eater still isn’t running smoothly, the carburetor adjustment may be to blame.

Most weed eaters have three small adjustment screws located around the fuel push button. These are usually marked with letters like "L," "H," and "LA" for low, high, and idle settings. Adjusting these screws controls the amount of fuel and air that enters the carburetor at different speeds. However, the correct adjustments vary depending on the brand and model of your weed eater. You’ll need to refer to the operator’s manual to see which direction to turn the screws and by how much. After making your adjustments, try starting the weed eater again and see if it runs more smoothly.

3. Spark Arrestor Screen

If your weed eater still won’t start or runs poorly, move on to check the spark arrestor screen on the muffler.

The muffler is a small metal component on the side of the engine where the exhaust exits. Inside, there’s a screen designed to catch any sparks or materials before they leave the engine—this prevents potential fire hazards. Over time, this screen can become clogged with carbon and debris, preventing the engine from breathing properly. A clogged screen can cause the weed eater to run poorly or not start at all. The screen is usually held in place by a single screw or clamp and can easily be removed and cleaned with a wire brush or solvent, or replaced if necessary. Once cleaned and reinstalled, test your weed eater to see if the issue is resolved.

4. Rewind Starter

If the weed eater still isn’t operating effectively, the next thing to check is the rewind starter—the pull cord mechanism that turns the engine over. You should feel a smooth pull with good recoil when using the pull cord. If the cord is difficult to pull or has lost its tension, the rewind starter may be faulty.

In many cases, replacing the rewind starter is an easy fix. You can purchase a new one and simply unbolt the old starter from the engine, then attach the new one in its place. If you’re more mechanically inclined, you can also try disassembling the rewind starter to inspect for any issues like a tangled or misaligned cord. Either way, fixing this issue should restore proper functionality to your pull cord.

5. Internal Shaft

Now, let’s say you’ve gotten the weed eater to run, but when you pull the trigger, the head doesn’t spin as it should. This is a more complex issue involving the internal shaft connecting the engine to the head of the weed eater.

To inspect this, disassemble the body of the weed eater by removing the head and checking the shaft that runs from the engine down to the cutting head. You can pull the shaft out or push it in to ensure it’s still in one piece and properly seated. Sometimes the shaft can become loose, either at the head or where it connects to the engine. If this is the case, simply reseat the shaft, reassemble the head, and test the weed eater again. If the head still isn’t spinning, you may need to replace the internal shaft entirely.

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By checking these five common trouble spots—your spark plug, carburetor, spark arrestor screen, rewind starter, and internal shaft—you’ll likely be able to troubleshoot most issues with your weed eater. With a little effort, you can often get things up and running again without too much hassle, potentially saving both time and money.