Hedge Trimmer: Won't Start

Your hedge trimmer has a switch that turns off the flow of power in the ignition coil to stop the engine from running. To check operation of the switch, remove the cover on the engine and locate the ignition module. Disconnect the 2 smaller wires to check switch operation. To do this, use an ohmmeter and turn the switch off and on. If you see the ohmmeter change, then the switch is in proper working condition. If it reads the same (no change), then the switch is malfunctioning and will need to be replaced.

A proper air/fuel mixture is essential for combustion in a two-stroke engine. The carburetor is designed to perform this task, and a damaged or clogged carb will prevent the engine from starting properly. To inspect and clean the carburetor, you will first need to locate it underneath the air filter. Next you can remove the air cleaner cap and look for any obstructions in the way that could block air flow, and starve the engine of oxygen. Unscrew the carburetor bolts and remove the fuel lines, then unhook the throttle cable from the carburetor linkage and pull the carburetor off. Clean the carburetor with carburetor cleaner and use a soft-bristled brush on the inside to remove any heavily gummed up deposits. At this point you should check the bowl for corrosion. If you notice corrosion, a new carburetor is required. You will also want to check that fuel is present at the fuel line entering the carburetor. Once you’ve either replaced or cleaned the carburetor, you can re-attach it to the engine. If the problem persists, you consider out directions for rebuilding carburetor under the “Carburetor Kit” section on this page.

The fuel filter is located inside the tank and prevents debris from entering the carburetor and engine, causing damage. You can remove the fuel filter but using a hook and pulling it out of the fuel tank, check to see if it is clogged as this can stop the flow of fuel to the engine. A visual inspection should tell you if there is a blockage, but you can also attempt to blow through it to check for a clog as well.

The spark plug creates the spark that ignites the fuel mixture. If the plug is worn or heavily damaged it will create a weak spark or no spark at all, which can prevent your trimmer from starting. Remove the spark plug and check for oily build up, heavy deposits, breakage, erosion, molting or any other fowling. A normal spark plug should be brown or light grey. If it is damaged, it will need to be replaced before your machine works at peak performance. Spark plugs should be replaced once per year as part of normal maintenance.

A carburetor kit contains the elements required to disassemble and rebuild your carburetor. It will not cause any problems directly, but installing a new carb kit is a great way to restore your carburetor to new condition, and keep your engine running smoothly. Fuel that sits for a long period of time, especially when it is mixed with oil, tends to gum up the inside of a carburetor. To install a new carb kit, simple remove the carburetor as explained in our section or the carburetor. Disassemble the entire carburetor, laying all the parts out on a table and making note of where they came from. Taking pictures along the way with a digital camera or cell phone is a great way to remember where the parts came from and how to reassemble them when the time comes. At this point, you can clean the entire carburetor housing with a carburetor cleaner and a soft-bristled brush. Be sure to clean all the gummed-up surfaces. Once you have reassembled the carburetor, just re-install it as described in the carburetor section. You will next need to set the low and high idle screws by turning them all the way till they shut off then back off 2 turns. Start the trimmer and let it warm up for about a minute, at which time you can begin to adjust the carb.

The purpose of the fuel lines is to deliver fuel from the fuel tank to the carburetor where it is mixed with air for combustion. If the fuel lines are badly clogged or cracked, the engine of your hedge trimmer may not start. To determine if the fuel lines are the issue, first pull the fuel line off the carburetor gently, using a twisting motion, and check that fuel is present. If no fuel is present then remove fuel lines to check for a blockage. Some models may require you to remove a rubber grommet on the side of the tank first where the fuel line connects. At this point, blow through the lines to see if they are blocked. If you notice a crack in the lines, they will need to be replaced. However, a clog may be able to be cleaned, allowing you to avoid replacement altogether.

The ignition module or ignition coil creates the electrical current that provides the spark plug with power to ignite the air/fuel mixture. To check the ignition coil and determine if it is working properly or not, first remove the housing and locate the ignition module. Follow the spark plug wire to the coil and disconnect the 2 smaller wires to check switch operation. You will need to use an oh meter to check the coil. Turn the switch off and on, if you see the ohmmeter change then the switch is good. You will also need to check the spark plug for a spark. To do this you can either use a spark plug tester or remove the spark plug and ground it on the end on the engine block. Then pull the starter rope to look for a spark. If there is no spark then remove the bolts holding the module in place and replace with the new module. Next you will need to set the gap between the module and the magnets on the flywheel. You will need a feeler gauge for this, and you will also need to know the manufacturer’s specifications for your machine. When this is completed, tighten the bolts down and hook your wires back up.