Standing in the hot sun, jerking on the rope of a lawn mower that refuses to fire up is not the way most homeowners want to start their weekend. While many different factors can cause this problem, most of them can be avoided with regular maintenance. Not only will a properly maintained mower start easier, it will cut better, last longer and contribute less air pollution.
Most starting problems can be traced to either a fuel supply problem or an ignition problem. If the fuel tank is full, and fuel is reaching the carburetor, make sure that the spark plug is tight in its socket and the spark plug wire is properly attached. If both of those seem in order, remove the spark plug and inspect the end for deposits and wear. To avoid this issue altogether, clean the spark plug and check the gap monthly, and install a new spark plug every 100 hours, or annually.
An engine that surges or lacks power does not have the proper air-to-fuel mixture. In most cases, the problem is with the air supply, rather than the fuel supply. Check and clean your air filter if your mower displays this type of behavior. Manufacturers recommend inspecting the air filter before each use and changing it every 25 hours or annually, whichever comes first.
Change the oil in your lawn mower every 50 hours or once a year, whichever comes first. Failure to do so will not likely result in any noticeable symptoms, until the motor fails completely. The oil lubricates the moving parts of the engine and cools it at the same time. Old, dirty, contaminated oil can't do the job right and will eventually lead to catastrophic failure.
Clean the Deck
Clean the deck after each mow. Most newer lawn mowers have a handle design that allows you to rest the deck upright, offering easy access to the underside. Hose it off with a stream of water and scrape off any tough residue that remains. If you have to place the lawn mower on its side, rather than back on the handle, always orient it so that the air cleaner is on the upper side. A dirty deck won't direct the flow of cut grass correctly and will cause corrosion of the deck structure.
Sharpen the Blade
Sharpen your blade at least once per season. If you see brown, ragged tips on your grass, your blade needs sharpening. If you sharpen the blade yourself, be sure to check its balance. Place the blade on a nail in the wall. If it will rest horizontally, it is in balance. If one side of the blade consistently drops, grind or file more off that side.
At the end of the mowing season, thoroughly clean the mower. Touch up any chipped paint. Wipe exposed metal with a rust-preventing lubricant. Apply a graphite, Teflon or silicone lubricant on throttle and choke cables. Drain the gasoline from the fuel tank (following the manufacturer's safety precautions). Start the mower and allow it to run until the engine burns all the fuel in the carburetor and fuel lines. Store your mower in a dry location, if possible.