After many hours of use, chainsaw motors often lose power and run slower. Owners frequently compensate by adjusting idle settings on the machine's carburetor, but changing idle speed or mixture doesn't fix the trouble. Ordinary maintenance usually puts the chainsaw back in good working order. Even a chainsaw that barely spins the chain may need nothing more than a thorough cleaning of critical filters.
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Chainsaws come equipped with a metal spark-arresting grid mounted over the outlet of the saw's muffler. This metal screen captures any burning carbon particles that blast out of the saw's exhaust, preventing accidental fires in the working area. Carbon in the exhaust gradually fills the pores of the screen and prevents exhaust gases from venting. A chainsaw with a clogged screen might start normally but barely run, showing no power and stalling when given extra gas. After all parts of the exhaust cool, remove the screen and thoroughly clean the spark arrester with a brass wire brush. Reinstall the spark arrester before using the chainsaw.
A dirty air filter at the other end of the system could also cause lost power. If the chainsaw loses power and produces thick exhaust fumes, the air filter probably needs cleaning. Removing the filter cover and air filter usually requires nothing more than a screwdriver. Air filters clog with spilled oil as well as with sawdust. Many filters have two layers, a sponge outer filter and a fine mesh inner filter, and each needs a thorough cleaning. A soft brush or a jet of compressed air clears the largest debris. For oil removal, wash the filters in a solvent approved by the saw's manufacturer.
If cleaning the air filter and exhaust port doesn't restore normal operation, check the chainsaw's spark plug. A spark plug in good working order shows a cylindrical metal electrode at the base of the plug with a clean gap between the electrode and a curved metal bar. If the plug shows no erosion or pitting and only small amounts of gray combustion products, the plug should work properly. Eroded parts or black, oily deposits mark a plug that needs replacing. Clogged filters or incorrect carburetor settings could cause carbon buildup on plugs. Adding too much oil to the fuel mix could also foul spark plugs.
Chain and Bar
Even a chainsaw with a motor in good working order can't power a dull chain. If a chainsaw stalls while cutting, the chain or bar may need work. As saw chains dull, the saw produces fine sawdust instead of shavings. This wood dust clogs the oil ports that lubricate the saw bar. Without enough oil reaching the bar and chain, friction increases. The chain could freeze up or break. Replace or sharpen saw chains as soon as cutting efficiency drops. Running a saw with a dull chain and an overheating bar could ruin the chain, the bar and the chainsaw motor.