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When a chainsaw won’t start, the cause can range from fuel issues to ignition faults or internal damage. Whether it’s a new chainsaw failing to fire or a well-used saw showing signs of wear, working through a step-by-step diagnostic process can help isolate the problem and restore function. This guide walks through a full inspection sequence—from basic fuel checks to deeper engine diagnostics—to help get your chainsaw back up and running.
Begin With the Fuel System
Start by mixing a fresh batch of fuel at the correct 25:1 ratio. Improper fuel mixtures or stale fuel are among the most common reasons chainsaws fail to start. Unscrew the fuel cap and inspect the fuel inside the tank. While there, examine the fuel filter for any clogs or debris that might be restricting flow.
Follow up by checking the fuel hose. Look for any signs of kinks, wear, or cracks. A damaged or blocked hose can prevent fuel from reaching the engine, so it’s important to ensure the line is clear and pliable.
Check the Air Intake
Next, remove the air filter cover and take out the air filter. Ensure the internal chamber is free of dust or blockages, and confirm again that there are no kinks in the connected hoses. A clean, unobstructed air path is essential for proper combustion.
Also, inspect the choke lever to verify it’s operating correctly. Check that the butterfly valve inside the carburetor is moving freely and not stuck in either the open or closed position.
Inspect the Spark Plug and Ignition
Remove the spark plug from the engine and inspect it for signs of wear. Measure the gap between the electrodes, which should be set to 0.7mm. If the gap is incorrect, it can lead to misfiring or a complete failure to ignite.
While the plug is removed, it’s also a good time to remove the sprocket cover and turn the sprocket by hand. This test helps identify if the clutch springs are seized or broken, which would prevent rotation.
To test for spark, connect the spark plug back into the ignition lead and make sure it’s seated firmly. Hold the spark plug electrode near a metal surface on the cylinder and pull the starter cord. A visible spark should jump across the electrodes.
If no spark is visible, disconnect the on/off switch and try again. Still no spark? The ignition coil may be faulty and should be examined next.
Test and Reset the Ignition Coil
To access the ignition coil, remove the necessary external cover. Check the condition of the on/off earth wire and confirm it is connected securely. Then disconnect the spark plug lead and remove the remaining cover to expose the coil and flywheel.
Measure the gap between the flywheel and the ignition coil magnet. This gap should be exactly 0.3mm. If an adjustment is needed, back off the mounting screws to widen the gap. Insert a 0.3mm spacer—such as a business card of equivalent thickness—into the gap, then retighten the screws with the spacer still in place. Remove the spacer once the screws are secure.
Once adjusted, refit the ignition cover and then the recoil cover.
Bypass the Carburetor
With the ignition system reset, add a small amount of premixed fuel directly into the cylinder—approximately one teaspoon. This bypasses the carburetor and feeds fuel directly into the combustion chamber.
Refit the spark plug, ensuring it is tight and properly seated. Pull the starter cord several times. If the engine fires, it confirms that spark and compression are present, and the problem likely lies within the carburetor.
Examine the Exhaust and Internal Components
If the saw still does not start, remove the exhaust. Check inside the muffler for any carbon buildup that may be restricting flow. Also inspect the cylinder for signs of scoring or carbon deposits. Turn the engine over a few times to assist with visual inspection and detect any abnormalities in piston movement.
Reset Carburetor Mixture Screws
Locate the carburetor mixture screws on the side of the saw. Turn each screw clockwise until it stops to reset the settings. Then back each screw off by one and a half turns. This returns the carburetor to its basic factory setting, which is suitable for diagnostic testing. At this point, idle settings do not need to be changed.
Test Compression
If the saw still fails to start after resetting the carburetor, conduct a compression test. Use a cable tie or similar tool to hold the throttle open. Then pull the starter cord approximately five times while observing the pressure gauge.
Normal operating compression should be between 91 and 110 psi. If compression falls outside this range, there may be deeper mechanical issues inside the engine.
When Further Diagnostics Are Needed
If none of the above steps resolve the issue, more advanced disassembly may be required. Internal air leaks caused by worn gaskets or faulty crank seals could be affecting performance. In these cases, the chainsaw will need to be stripped down for inspection of the bottom-end components.
By following this complete checklist, users can identify the most common causes of chainsaw failure—ranging from simple fuel mix problems to more complex ignition and compression faults. Each step builds upon the last, helping isolate the issue systematically without guesswork.
