You’ve been putting off trimming those tree limbs for long enough, but now that you’ve found the motivation to tackle the job you discover your gas-powered chainsaw won’t fire up. You’ve filled the tank with fuel and pressed the primer bulb repeatedly, but no matter how many times you pull the starter rope the chainsaw just won’t start. As you might have guessed, there is more than one reason why your chainsaw engine refuses to turnover and we’ll get to those right after a brief review of how a gas-powered chainsaw operates.
How a gas-powered chainsaw operates
While there are electric chainsaws on the market powered by an extension cord or battery, most landscaping professionals and dedicated DIYers rely on the more heavy-duty gas-powered models.
Gas-powered chainsaws utilize a two-cycle engine to operate
Most gas-powered chainsaws 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 a chainsaw is a piece of hand-held equipment designed to be held at different angles to saw through tree limbs and firewood, a two-cycle engine is ideal for this application.
How a gas-powered chainsaw starts up
To start the chainsaw 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.
Clutch flyweights extend outward to rotate a gear to drive the chain
The crankshaft of the chainsaw’s engine extends out the side of the crankcase and connects to a centrifugal clutch. At idle speed, the engine will run but not fast enough to engage the chain. When the throttle trigger is pressed, the engine accelerates, causing the clutch flyweights to extend outward and begin to rotate a drive gear attached to the chain.
The chain runs in a track on a bar
The chain rides in a track on a bar. As the clutch rotates, it also operates a pump to supply chain oil to the bar. This specially formulated chain oil is thick and designed to stick to the bar and chain, so be aware that standard engine oil should never be used as a substitute. The oiler hole (where the chain oil excretes from) should always be kept clear of debris to ensure proper lubrication; otherwise, the bar, chain, or engine could become damaged.
5 probable causes of a gas-powered chainsaw not starting
Now that you know how a gas-powered chainsaw operates, you’ll be more successful at troubleshooting why the chainsaw won’t start. Here are the top five most probable causes Repair Clinic recommends you investigate:
- 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 chainsaw. 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.
- 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 chainsaw’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.
- Clogged fuel filter – Old or bad fuel can also create a clog in the fuel filter which can prevent the chainsaw from starting as well. A clogged fuel filter is difficult to clean; however, they are relatively inexpensive and fairly easy to replace.
- 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 chainsaw engine not starting. Many recoil springs and pulleys can be replaced individually, but it may be easier to replace the entire recoil starter.
- Malfunctioning recoil starter – The recoil starter itself could be malfunctioning and unable to engage with the chainsaw engine crankshaft. Again, you can replace the recoil starter with a new one to resolve the issue.
The chainsaw repair help you’ve been looking for
Searching for more chainsaw repair info and troubleshooting tips? Check out the Repair Clinic website’s “Videos & Articles” section for the chainsaw repair help you’ve been looking for. You’ll find equipment schematics, step-by-step guides, and detailed procedural videos, including one showing you how to install new oil pump kit components on a Craftsman Chainsaw (Model 358350982), or the right way to replace the on-off switch on a Homelite Chainsaw (Model UT10584).
Whatever repair you need to perform on your chainsaw, Repair Clinic recommends using only original equipment manufacturer (OEM) parts to ensure the chainsaw is fixed right the first time. To find all the genuine OEM parts that match your particular chainsaw, enter the equipment’s full model number in the Repair Clinic search bar. This will result in a list of all compatible parts which you can then refine by using the “Part Category” navigation filter (examples: “Engine”, “Chain & Bar”) and “Part Title” filter (examples: “Flywheel”, “Chain Tensioner”). With a warehouse filled with lawn and garden equipment, appliance, and HVAC replacement parts, plus repair help guidance throughout its website, Repair Clinic considers itself a trusted year-round repair partner.