Small Engine Maintenance: Keep Your Outdoor Power Tools Running
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Small engines on lawn mowers, trimmers, blowers, and chainsaws are mechanically simple, and most maintenance tasks take 15 to 30 minutes with basic tools. The biggest cause of small engine problems is stale fuel, followed by neglected air filters. Both are easy to prevent.
Oil Changes
Four-stroke engines (most lawn mowers, some trimmers and blowers) need oil changes. Check your owner's manual for the interval, but 25 to 50 hours of use or once per season is typical for residential equipment. You need a drain pan, the correct weight oil (usually SAE 30 or 10W-30), a funnel, and rags.
Run the engine for a few minutes to warm the oil before draining — warm oil flows out more completely. Remove the drain plug or use the oil drain tube if your mower has one. Fill with the specified amount of new oil and check the level with the dipstick. Overfilling causes as many problems as underfilling. Two-stroke engines (many chainsaws, some trimmers) mix oil with fuel and don't need separate oil changes.
Air Filters
A dirty air filter starves the engine of air, causing poor performance, hard starting, and increased fuel consumption. Check it every 25 hours of use. Paper filters get replaced — don't try to clean them. Foam filters can be washed in warm soapy water, wrung out, and re-oiled with a light coat of clean engine oil.
The air filter housing is usually held on by a single screw, wing nut, or clip on top of or beside the engine. Open it, inspect the filter, and replace or clean as needed. This takes less than five minutes and is probably the single highest-impact maintenance task for reliability. Keep a spare filter on hand so you're not making a parts-store run on mowing day.
Spark Plugs
Replace the spark plug once per season or every 100 hours. You need a spark plug socket (usually 13/16 or 3/4 inch), a ratchet, and the correct replacement plug. Check your manual for the plug number and gap specification. A spark plug gap tool sets the gap — most small engines spec 0.030 inches.
Before removing the old plug, blow debris away from the plug area with compressed air so dirt doesn't fall into the cylinder. Hand-thread the new plug to avoid cross-threading, then snug it with the socket. Don't overtighten. A worn or fouled spark plug causes hard starting, misfires, and poor fuel economy. If the old plug is oil-fouled or the electrode is heavily worn, it's overdue.
Fuel System
Stale fuel is the number one cause of small engine problems. Gasoline starts degrading after about 30 days. Ethanol-blended fuel (E10 and higher) is worse because ethanol absorbs water from the air. Use fuel stabilizer in every fill-up if your equipment sits between uses for more than a couple of weeks.
At the end of the season, either run the engine dry (let it run until it stalls from lack of fuel) or fill the tank completely with stabilized fuel. A half-empty tank with untreated fuel over winter is the recipe for a carburetor rebuild in spring. If your engine has a fuel filter, replace it annually. Inline fuel filters are cheap, and a clogged one causes starvation symptoms that mimic carburetor problems.
Seasonal Storage
Before putting equipment away for winter, do all the maintenance at once: change oil, replace or clean the air filter, replace the spark plug, treat the fuel, and clean the exterior. Scrape grass buildup from the underside of the mower deck with a putty knife — packed grass holds moisture against the deck and promotes rust.
Store equipment in a dry space, off the ground if possible. Remove the battery from battery-powered equipment and store it at room temperature at about a 50% charge. Disconnect the spark plug wire on gas equipment to prevent accidental starting. Hang string trimmers and blowers vertically to save floor space. A few hours of maintenance in the fall prevents frustration and repair bills in the spring.
Frequently Asked Questions
Can I use ethanol-free gas in my lawn mower?
Yes, and it's recommended if you can find it at a reasonable price. Ethanol-free gas doesn't absorb water, doesn't degrade as quickly, and won't damage rubber fuel system components the way ethanol-blended fuel can over time. It's especially worth using in equipment that sits between uses, like a chainsaw you only run a few times a year. It typically costs 50 cents to a dollar more per gallon.
How often should I sharpen my lawn mower blade?
Every 20 to 25 hours of mowing, or about every two to three weeks during peak season. A sharp blade cuts cleanly, producing a healthy lawn. A dull blade tears grass, leaving ragged brown tips. You can sharpen the blade with a bench grinder, a file, or a drill-mounted blade sharpener. Remove the blade first — never try to sharpen it while mounted on the mower.
My mower won't start after winter storage. What should I check first?
In order: stale fuel (drain and refill with fresh gas), spark plug (remove, inspect, replace if fouled), air filter (replace if dirty), and battery charge (on electric-start models). Stale fuel is the cause about 80 percent of the time. If those four things don't fix it, the carburetor probably needs cleaning. A carburetor rebuild kit costs about 15 dollars and the job takes about an hour.