Whether you have an old mower that hasn't been used in a long time or just received a hand-me-down, you are guaranteed to encounter times when it won't start. Lawn mowers that have been maintained but not used for a long period have a higher chance of starting than those that are long-neglected. Many mowers suffer from fuel problems or old spark plugs, both of which are inexpensive and easy to fix.
Remove old grass that has been caked around the blade and underneath the mower by scraping it with a wooden stick or screwdriver. Spray the mower blade shaft with WD-40 to lubricate it for better movement.
Install a new spark plug as it is an inexpensive maintenance step. Remove the old spark plug by unscrewing it from the mower with a wrench. Spray a half spray (approximately one second) of starting fluid into the spark plug hole. Screw a new spark plug in the mower with your hand and tighten with a wrench.
Verify the gas level in the mowers tank by looking inside the tank and gently moving the mower to see if there is fluid inside. Empty the gas and add fresh if it is older than three months. Drain the gas into a container and take it to a waste recycling center. An engine that starts but stalls out is a symptom of old gasoline.
Set the lawn mower throttle to choke and pull the starter cable. You may need to pull the cable several times to get the mower to start. The choke location varies depending on the manufacturer of the lawn mower. Some mowers have a choke on the handle bar while others are located near the engine. The choke is a lever that controls the amount of air entering the carburetor.
Stop trying to start the mower if the engine becomes flooded of gas. Let the mower rest for at least 15 minutes to allow the gas to evaporate. A gas flooded engine will not start and you will smell a strong scent of unburned gas. Try to start the mower with the choke set to off after the rest period.
Remove the spark plug and spray a half spray (approximately one second) of starter fluid into the spark plug hole if the mower still doesn't start. If the mower begins to run but chokes out, the carburetor may be clogged.
Remove the air filter to see if it is dirty. Try starting the mower with the air filter off. Replace the air filter if it starts while it is removed.
Look into the carburetor while attempting to start the mower with the air filter off if the mower still does not start. The float is stuck if gas spurts out of the carburetor. The float is under the carburetor and can be accessed by removing the float nut and dropping the bowl covering down. Verify the float moves up and down easily. The mower requires repair if the float does not move freely. Wear protective eye gear to prevent gas from getting into the eyes accidentally.
Make a decision as to whether it is worth fixing the old lawn mower that won't start. An electrical or carburetor problem may not be worth fixing. Consult a professional on the cost of repair and evaluate if a new mower is more economical than fixing an older one.