Why Is My Lawnmower Starting & Then Going off in a Couple Seconds?

Check the Gas

• The supply of fuel is critical for the mower to start and stay running, so always make sure the mower has a full tank of fresh gas before starting it. Bad gas, or old gas, when used in your mower, sticks to the hoses and walls of the fuel system, eventually choking the fuel supply off. Bad gas accounts for a majority of start-up problems. Gas left in a mower over a long period, more than 30 days, will also break down and clog the fuel system. Properly dispose of old, unused fuel in the tank and your container and start with fresh gas.

Check the Oil

• Oil supplies the crankcase and piston with the lubrication needed to keep them moving fast and hot. Without a full supply of oil, the mower will quickly start heating up. Many modern mowers operate with a safety shutoff switch that will shut the mower down before serious damage occurs. Remove the oil dipstick and check the supply of oil in the crankcase. If it reads low, add more oil according to the manufacturer's recommendations for your brand and model, because they vary.

Clean the Air Filter

• A dirty air filter will also cause the mower to shut off after a few seconds of operation. As the mower starts running, it needs to start burning a greater amount of fuel. To consume this fuel, a greater amount of air is also necessary to properly dilute the fuel to its highest combustion level. If air can't flow through the filter, the increase of fuel will cause the mower to shut off. Remove the foam element inside the air filter box and clean it according to your mower's manufacturer's specifications.

Check the Fuel System

• Mowers operate in dirty conditions, and the entire engine needs to stay clean inside to keep working. Any particulate matter, such as dust or grass clippings, can't enter the fuel or air system without causing problems such as this. When the fuel cap gets removed for a refill, always wipe the cap, threads on the tank and the area around the tank with a rag. This will prevent debris from falling into the tank and getting trapped in the fuel system. If problems continue, allow a professional to service the rest of the fuel system.