Troubleshooting Common Malfunctions in Hedge Trimmers

Like virtually any other power tool, hedge trimmers also have their share of malfunctions and issues related to engine performance, etc.

For those of you who don’t possess even the most basic technical knowledge, identifying the issue with your hedge trimmer and fixing it can be a frustrating affair.

But don’t lose hope – this guide will provide you with the fundamentals of hedge trimmer troubleshooting.

Common malfunctioning issues

The most common problems pertaining to hedge trimmers not working include: not starting properly, running rough and starting then abruptly stopping.

I will examine each issue and explain what techniques you can apply to troubleshoot them.

Hedge trimmer won’t start

Defective spark plugs are often a major reason why hedge trimmers won’t start. If this is happening to you, I recommend inspecting the device’s spark plug to see if it is wearing out or has been damaged. If so, you will have no other choice but to replace it.

In order to know if a spark plug is faulty, determine that with a spark plug tester. If there is a strong spark between the tester’s terminals when the engine is cranking, the spark plug is working fine. On the other hand, if there is no spark, purchase a new one.

Another common factor in a hedge trimmer not starting is a clogged carburetor. This happens when fuel is left inside the engine for an extended period of time. This fuel becomes stagnant – and thick and clogs up the carburetor. Thus, you must regularly clean your hedge trimmer’s carburetor.

If you cannot do this, you should replace the carburetor or rebuild it yourself if you have the ability to.

Your hedge trimmer runs rough

The same culprit that is often to blame for hedge trimmers not starting properly is also commonly the cause of these machines running rough. Yes, I’m talking about a clogged carburetor. Another issue that causes running rough is a clogged fuel filter.

This is also caused by leaving old fuel in the hedge trimmer for too long. It becomes very sticky and thus clogs up the fuel filter, which in turn gives the engine plenty of grief.

Troubleshooting tips for this situation include draining the old fuel from the fuel tank and replacing the fuel filter.

Hedge trimmer starts then abruptly stalls

Again, a clogged carburetor is a common cause of an engine starting fine then abruptly stalling or stopping after a few seconds.

While I suggest using troubleshooting techniques listed above to fix this issue, you can also purchase a carburetor repair kit. This kit provides the essential tools you need for fixing your defective carburetor.

Additionally, a clogged arrestor screen can also cause the engine to start then stop. This part of the hedge trimmer is a small screen designed to prevent the engine from giving off sparks.

What commonly happens is that the arrestor becomes clogged with soot over long periods if not cleaned regularly. If your screen arrestor is clogged, remove it and use a wire brush to clean it well. If this doesn’t work, the best advice I can give you is either replace the spark arrestor or take your hedge trimmer to a dealer where a professional technician will fix it for you.

Blades not turning

Another common malfunction in hedge trimmers are when the blades don’t turn properly. If the blades are not moving, your clutch may be damaged or simply in need of tensioning.

The clutch is attached to the crankshaft. The two work together to start rotation once a certain level of revolving speed has been reached. Unless you have a considerable amount of knowledge in this area, fixing a broken clutch isn’t really practical.

Replace it instead. In order to remove a broken clutch from your hedge trimmer, you need to disassemble the engine shrouds in order to gain access.

Depending on the brand and model of hedge trimmer you own, you should remove the spark plug, and place rope into the combustion chamber to prevent the piston from moving while the clutch is being removed. If you are unsure if you are this procedure properly, refer to the user manual for step-by-step instructions.

To sharpen the blades, place the hedge trimmer in a vise on a surface with the blades facing up. Use a rotary tool with a sharpening pad on the end to grind the edges of the blades. Do this for five – ten minutes.

Once that is over, place lubricating spray on the edges of the blades before taking the hedge trimmer from the vice.

If you need more instructions for sharpening your blades, check out this article I wrote.

A word about the gearbox of a hedge trimmer

The gearbox is located near the bottom of the engine, where the blades are directly attached. The gearbox works by allowing gear reduction, which transfers rotational motion back and forth to enable the blades to operate correctly.

When a hedge trimmer’s gearbox doesn’t work right, it’s often because of stripped gears that are wearing out or the jamming of blades.

The hedge trimmer runs but will not cut

Although not wholly common, this issue is still a bane for hedge trimmer operators. You’re probably wondering what exactly causes a hedge trimmer to run but not cut hedges and shrubs.

When debris such as heavy volumes of grass or twigs get caught between the cutters and become built up over time, they get clogged.

Has this ever happened to you? You plan to spend a nice fall or spring day trimming your hedges and then, all of a sudden, you’re left frustrated, not knowing what to do?

In this case, turn off the trimmer and clean out every bit of debris you find inside. Afterward, use a damp cloth to clean the blades and grease the cutters with a light oil. If this fails to work, you may need to get the cutters fixed.

Motor overheating

One thing your motor absolutely detests is when you shove the hedge trimmer into heavy brush. This causes the motor to have a shortage of airflow.

When that happens, it becomes overheated. The only troubleshooting technique you can apply in this case is to shut off the trimmer and allow it to cool down before going back at whatever job you were doing.


I hope that you will find these troubleshooting techniques useful. Remember, if you are not comfortable or do not have the mechanical knowledge to fix an engine, motor, etc. I highly advise you to hire a professional to get it done.

Peter Toth

Hi! I'm Peter, the owner of BackyardGadget. Working around the house has always been a big part of my life. I've created this site to share my experience, and to help people choose the right tools for the job. Thank you for stopping by!

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