Lawn mowers, whether electric or gas, can have many problems. Whether the mower doesn't start, has problems running or doesn't cut well, it's important to find the cause. There are a range of solutions that can be simple fixes to many of the problems with lawn mowers.
If the motor doesn't turn over at all, check the fuel, oil or electrical connections. If the motor tries to start but fails, look for clogs in the carburetor or air filter and make sure the electrical connections (such as the spark plug wire or power cord) are secure. Adjust the choke or throttle if the motor sputters. Check the mower blade to ensure nothing is blocking or catching it, such as excess grass or debris. If the motor backfires or sparks, replace the spark plug or solenoid that holds the initial charge to start the mower. Change the battery if nothing else is causing the problem.
If the mower starts and then stops suddenly, look for debris caught in the motor housing and check to see if the power cord came unplugged. Check the fuel or battery if the motor loses power and stops. If the mower bogs down or the motor stalls, the grass is too high or too thick for the mower; back up the mower and try mowing more slowly at a higher blade setting.
If the grass is showing jagged rough edges after mowing, check the blade for sharpness. You'll also see jagged edges if the grass is too wet. Finding clumps of grass indicates the mower is cutting too fast or the grass is wet. Uneven grass heights means the mower deck or blade is uneven; tighten the blade or adjust the height of the mower deck to be even in both front and back. Grass is not discharging properly is a sign of a clogged shoot or debris stuck around the blade. Loud noise followed by the motor stopping means the blade and rod has been damaged and needs replacing.
Seeing dark smoke from the motor is a sign of burning oil. Seeing light smoke from the motor is a sign of burning gas or water in the fuel/oil or a short in the electrical connections. Stop the motor immediately if you see either type of smoke. Rough sounding motors indicate old fuel or oil; replace the fluids and clean the carburetor and air filter. Replace the muffler should the motor sound extremely loud. If the starter cord sticks or pulls hard, check for debris in the top of motor housing. If the cord fails to move or hangs after pulling, it needs to be rewound.
If the motor housing moves while pulling the starter cable, check the bolts holding it to the mower deck; re-drill the bolt holes or replace the deck. If the deck shakes or shimmies, tighten the bolts or replace the deck. Tighten the wheels regularly because the bolts holding them work loose, causing uneven mowing.
Dark fuel or oil can clog the motor with buildup and debris; change the fuel and oil regularly. Drain the oil and fuel before storing the lawn mower for winter to avoid the liquid from gumming up the motor. If the spark plug fires but the motor doesn't start, you could have a clogged carburetor or air filter that is not allowing fuel to reach the motor. If the exterior of the motor housing is burnt, it may be covered with a coat of fuel or oil. Tipping the mower to the side where the oil or fuel fill holes are may cause leaks in liquid.