It costs a lot to repair a lawn mower, so it makes sense to repair the mower yourself if you can. Do-it-yourself lawn mower repair requires only that you know the basic parts of the mower and where they are located and be able to clean and replace some common parts. First you must diagnose the problem.
Lawn Mower is Lacking Power
Never start the new mowing season with gas left in the mower from the previous season. Check the gas, and empty the old gas. Old engine oil can cause the same problems as old gas. Check the oil and change it if necessary. Check the spark plugs, and replace them if they are old or damaged. Check that the air filter is not too dirty, and replace it if necessary. Lubricate the mower if it has not been properly oiled. Make sure the valves and piston rings are properly sealed. Check the choke, and clean it if it is clogged. Check and replace the head gasket if it is worn or blown.
Lawn Mower Vibrates or Overheats
A lawn mower will vibrate if the engine is not properly mounted. Unscrew it, straighten it out and remount it. It will also vibrate due to a bent crankshaft or a counterbalance that is not timed properly. These conditions are complicated to repair and will require that the mower be serviced. The engine could be overheated if it is making a knocking sound. Check that the flywheel and connection rod are secure. The engine also could be overheating because carbon has built up, which can be cleaned out.
Lawn Mower Dies After Starting
Make sure you have enough clean fuel if your lawn mower dies after starting. Check the muffler, and clean it if it is clogged. Check the air filter, and clean or replace it if necessary. Check the mower shut-off valve, and if it is closed, open it. The fuel tank vent might be blocked and have to be cleaned. The lawn mower might die due to a bad carburetor. Take it to be serviced or replaced.
Lawn Mower Will Not Start at All
Check that the ignition switch is turned on. A cutoff switch is on some mowers for safety, and if defective, the mower will not start. Make sure the mower has fuel in it if it will not start. If it does have fuel, the engine might be flooded. Turn off the fuel and restart the engine. After you have it started, turn on the fuel again. Try emptying the tank and then refilling it. Check the throttle setting to make sure you started the mower on the correct setting. Make sure there is no water in the tank. Make sure there is no old gas in the tank from the previous season and replace if necessary. Check that the terminal covers are not loose and are still covering the spark plugs tightly. Clean the spark plugs, and replace defective plugs.