7 Reasons Why Your Hedge Trimmer Won’t Start

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Professional landscapers, as well as homeowners who aspire to keep their yard immaculately manicured, know that a hedge trimmer is a crucial component in their landscape maintenance arsenal. Sure, hedge trimmers keep the hedges even, but this versatile tool is also ideal for trimming small shrubbery, pruning perennials, weeding, and helping small trees retain their shape.

However, that versatility is of little use if your hedge trimmer refuses to start. There are seven likely causes of a gas-powered hedge trimmer not starting, which we’ll address below right after providing some context of how a hedge trimmer works.

The basics behind how a gas-powered hedge trimmer works

While electric hedge trimmers can be powered by an extension cord or battery, most gas-powered trimmers rely on a two-cycle engine to operate. Two-cycle engines require the gasoline to be mixed with oil for the engine to function properly. Attempting to run a two-cycle engine without a suitable gas and oil mixture will cause the engine to seize due to insufficient lubrication. The main benefit of a two-cycle engine is that it allows for a high output of torque while being relatively lightweight. Since hedge trimmers are intended to be hand-held and operated at varying angles to trim and shape hedges, small trees, and shrubbery, a two-cycle engine is ideal for this purpose.

To start the hedge trimmer engine, the ignition switch must be set to the “start” position. As the starter rope is pulled, the starter engages the drive cup on the engine’s flywheel and rotates the crankshaft. The rotating crankshaft connects to a piston which moves up and down within the cylinder and the ignition process begins. The flywheel has permanent magnets built into it and as it rotates past the ignition coil, a magnetic field is created. This magnetic field induces electricity, allowing the ignition coil to send voltage to the spark plug. As the piston travels down the cylinder, it exposes an intake port and pumps fuel, oil, and air into the cylinder. As the piston travels back up the cylinder, a vacuum is created and gas, oil, and air is drawn through the carburetor into the crankcase. When the piston reaches the top of the cylinder, the spark plug ignites the compressed fuel and air mixture which forces the piston back down, exposing an exhaust port where the spent fuel exits. A split-second later, the intake port is exposed again, fresh fuel is drawn in, and the process is repeated with every revolution of the crankshaft.

The exhaust from the hedge trimmer engine travels through a muffler and a spark arrestor. The muffler reduces engine noise while the arrestor prevents burning carbon deposits from exiting the engine and causing injury or potentially starting a fire if the surrounding grass is dry. Two-cycle engines typically have a choke, primer bulb, or both, to assist with starting, especially when the engine is cold. The choke will temporarily restrict airflow through the carburetor so more fuel can enter the cylinder. Likewise, when the primer bulb is pressed, it will draw additional fuel through the carburetor which enters the cylinder before the engine is started.

When the operator squeezes the throttle trigger, the engine will increase speed from idle to run and the clutch will engage the clutch drum with its drive gear. The clutch drum drive gear engages the blade drive gear and the blades begin to oscillate. The action of the blades moving back and forth allows the trimmer to cut through small branches on bushes and hedges.

Hedge trimmer not starting? 7 probable causes

When troubleshooting why your hedge trimmer is not starting, here are the seven most likely causes you should investigate:

  1. Defective spark plug – Due to carbon build-up or a weakened electrode, a spark plug will degrade over time and be unable to ignite the compressed fuel and air inside the engine’s combustion chamber to start the hedge trimmer. You can use an ignition tester to help determine the strength of the spark plug, but it’s probably easier to simply replace the spark plug with a new one, something we recommend doing annually.
  2. Restricted carburetor  –  Old or bad fuel can leave a gummy residue inside the carburetor creating a restriction. This will prevent the proper ratio of fuel and air from entering the cylinder which can cause the engine to have trouble starting. You should always make sure you keep fresh fuel in the tank and avoid using fuel that contains more than 10% ethanol. We also recommend using a fuel stabilizer to help preserve its quality. If you’re concerned about getting that gas/oil balance right for the trimmer’s two-cycle engine, you can use a pre-mixed fuel and oil product like TRUFUEL 50:1 Mix to fill the tank. You can try cleaning the carburetor ports with a dedicated carburetor cleaner, or WD-40, to clear out the restriction, but if the clog is particularly bad, you may need to purchase a new carburetor.
  3. Clogged fuel filter – Old or bad fuel can also create clog in the fuel filter which can prevent the trimmer from starting as well. A clogged fuel filter is difficult to clean; however, they are relatively inexpensive and fairly easy to replace.
  4. Damaged recoil spring or pulley – If the starter’s recoil spring or pulley is damaged, the rope won’t be able to recoil onto the pulley, which will result in the trimmer engine not starting. Many recoil springs and pulleys can be replaced individually, but it may be easier to replace the entire recoil starter assembly.
  5. Malfunctioning recoil starter – The recoil starter itself could be malfunctioning and unable to engage with the trimmer engine crankshaft. Again, the starter assembly can be replaced to resolve the issue.
  6. Clogged spark arrestor – This small screen located near or on the muffler, which is designed to prevent sparks from spitting out of the engine, can become clogged with soot after numerous hours of use. This can interfere with the engine starting. While you can try cleaning the arrestor with a wire brush, replacing the arrestor with a new one may be more effective.
  7. Dirty air filter – A dirty air filter may prevent the hedge trimmer from starting as well by restricting the air coming into the carburetor. As with the spark plug, the air filter should be replaced annually or whenever it is visibly soiled.

Genuine OEM hedge trimmer parts direct from Repair Clinic

When replacing a part to repair your hedge trimmer or the trimmer’s engine, you want to make sure you’re purchasing a genuine OEM part, not a cheap knock-off, to keep the equipment running optimally. This is why Repair Clinic.com is your best source for replacement parts. Repair Clinic carries only genuine manufacturer components from the top names in outdoor power equipment, including Craftsman, Cub Cadet, Dolmar, Echo, Homelite, Husqvarna, Kawasaki, MTD, and Poulan. You can find the right part for your hedge trimmer by entering the trimmer’s full model number in the Repair Clinic website search bar, then use the navigation filters to narrow the resulting part list down to identify the specific part you’re looking for.

As your repair partner, Repair Clinic provides even more support by offering an extensive “Repair Help” library filled with thousands of free videos, articles, schematics, and diagrams. This wealth of material will assist you in troubleshooting any problem you may be experiencing with your outdoor power equipment, home appliance, or heating and cooling system, as well as show you, step-by-step, how to replace a defective component.

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