How to Troubleshoot Issues With Your Lawnmower

Lawn mower in garden
Jan Hakan Dahlstrom / Getty Images

Gas-powered lawnmowers are great when they run, but they can cause a good deal of frustration when they do not. There are many different components working together within any lawnmower, and figuring out which one is causing the problem is not always the easiest task. To aid in your efforts, we have compiled a list of common problems lawnmowers experience and ways you can troubleshoot to start your mowing season off without a hitch.

The Engine Will Not Crank

If your engine will not crank at all, the cause is probably simple.

Check for Safety Features

Typically, no crank at all comes down to an engaged safety feature on the mower. On riding mowers, check to ensure the blade is disengaged, the parking brake is engaged, and make sure you are seated on the mower when attempting to start, as many models feature contact points under the seat as an added safety measure. On push mowers, ensure the safety lever is fully depressed. Safety features vary from model to model, and you should adjust this process according to your manual.

Test the Battery

If the mower has a battery, this is the next thing you should check. Use a battery charger with a tester, or a multimeter, to ensure the battery is functional. If it is, ensure the battery is fully charged and that the terminals are clean and have a good, tight connection with the black, negative cable attached to the negative terminal and the red, positive cable attached to the positive terminal. If the mower still will not start, check all fuses and wires to ensure there are no bare, loose, or pinched wires. Replace blown fuses with properly rated automotive fuses.

Warning

Before servicing a lawnmower, it is recommended that you remove the spark plug to avoid accidental ignition.

The Engine Cranks But Does Not Start

Examine the Fuel System

If the mower has a good, strong crank and still will not start, begin by examining the fuel system. First, make sure the mower has gas. If the mower has not been used recently, it is not a bad idea to replace any existing gas with fresh gas. If the mower has gas, there may be a reason that it is not reaching the spark plug. Ensure all fuel lines and filters are clean and replace if damaged or clogged. If your mower has a fuel shutoff valve, make sure this is in the on position. Lastly, ensure the priming bulb is pumped to draw gasoline into the carburetor.

Fix the Choke

Lawnmowers feature chokes that can be adjusted to help the mower start and run. The choke controls the air to fuel ratio. Your manual will give insight into how to start your specific mower, including the proper position for the throttle and choke. If you do not have the manual or otherwise cannot find this position, start by placing each at the halfway mark and adjust as you attempt to start. If you still are not seeing results, remove the air filter and replace if dirty.

Don't Forget the Spark Plug

If all else fails, the next step is to check your spark plug. Start by removing the spark plug and inspecting it. If the spark plug is wet, this is a good indication that fuel is reaching it. If it is dry, fuel likely is not properly cycling. Ensure the gap at the end of the plug is clear and test the spark plug using a spark plug tester. Replace if you do not see a spark. When replacing the plug, carefully screw it into place to avoid cross-threading.

The Engine Runs for a Second, Then Dies

Consider the Carburetor

Carburetor issues are a common reason lawnmowers and other small engine tools will run for a few seconds, but ultimately die. As lawnmowers age, the carburetor moves a lot of air and fuel. This wear and tear can wreak havoc on the microscopic components, leading to clogging that restricts the engine's air and fuel.

While carburetors can be cleaned and rebuilt, many lawnmowers have available replacement carburetors that are prebuilt and ready to go. Carburetors are complex and, if you do not have much mechanical experience, it may be a good idea to leave this job to a professional. Other reasons a mower might stall after running are dirty air and fuel filters or fuel lines.

What Is a Carburetor?

A carburetor is a device that combines air and fuel inside of an internal combustion engine. It features tiny holes and components that can easily become dirty and clogged and often requires maintenance or replacement.

The Engine Is Smoking

Check Oil Levels

If you see smoke rising from your lawnmower, it is likely a result of too much oil being added. Remove any excess oil, ensuring the oil level is adequate before starting. This could also be a result of oil getting into places it should not, which could be due to worn or damaged parts.

Test the Compression

Ensure the mower has proper compression by using a compression tester and comparing it to the specific engine's specs. If you do not have this specialty tool, visually inspect to the best of your ability. Ensure that the oil dipstick is properly seated, the dipstick tube is not damaged, and inspect the valve cover for leaks. If you suspect the engine is losing compression, it likely should be taken to a professional for repair.

Mower Vibrates and Shakes When Running

Inspect the Large Components

If your lawnmower runs but vibrates and shakes, this is likely due to damaged or worn components.

Warning

Heavy vibration or shaking of a running lawnmower is a good sign of a potentially dangerous issue. Loose nuts, bolts, or components can dislodge and cause serious injury. Don't operate a lawnmower in this condition. If the problem can't be identified and repaired, have the mower professionally serviced.

Inspect all blades, pulleys, and spindles for wear and damage, and replace them if necessary. Belts should be inspected on a regular basis, especially after long storage periods such as the winter season. Ensure all mounting bolts are tight and grease points are properly greased.

Tip

If your mower struggles or even stalls while mowing, adjust the height of your deck. Thick and tall grass can put a heavy load on small engines. If the grass is too tall, too thick, or even too wet, adjust to full height, then make multiple passes, lowering the deck as you go.