Spark plugs every season. Air filters when they look dirty.

Replace the spark plug once a year or every 50 hours of run time, whichever comes first. Air filters are different—check them every few tanks of gas and swap them when they’re visibly grimy or clogged. A clean filter keeps the engine running right; a dirty one makes it run lean and hot.

An annual spark plug change is cheap insurance. A new plug costs a few bucks and takes five minutes. Ignore it and you’ll get hard starts, misfires, and eventually a dead saw.

Air filters are wear items. If you cut in dry, dusty conditions, clean or replace after every use. If it’s just occasional firewood, you can go a whole season. But don’t wait until the saw starts bogging down—by then you’ve already been running dirty.

Future You will appreciate not fighting a saw that won’t start.