Riding Lawn Mower Won’t Start? How to Fix

A riding lawn mower employs mechanisms that are quite simple to understand and work with. When it doesn’t start, finding the reason behind it isn’t that hard. With an understanding of the parts of the lawn mower and some time on your end, it’ll be up and running in no time.

Your riding lawn mower won’t start due to lack of fuel, the gas valve being off, choke fault, plug issues, battery issues, air filter issues and many others. While some require simple changes in settings, others require the replacement of the faulty parts.

Whether your mower cranks but doesn’t start or is completely silent when you try to start it, we have a list of the causes and their respective solutions. At times, you may have gone through all the startup items for the mower yet it still doesn’t start.

Why a Riding Lawn Mower Won’t Start

Here are reasons why a riding lawn mower won’t start and how to fix

1. Little to no fuel

An easy one to start with, your mower’s engine needs fuel to start and run. A lack of it means that the engine won’t start and, even when it does, it’ll likely shut down after a short while. Check the fuel gauge and if it indicates a low reading then that’s probably the cause.

Solution

For fuel, the solution is to refill the tank then crank the engine for a while before starting it again. However, how fast you fix this will depend on the kind of fuel your lawn mower use.

If you don’t have fuel in the mower, you’d be okay if it’s gasoline (petrol) or ethanol. For this type of fuel, a simple refill will do the trick. If it’s diesel and you tried to start it without fuel, however, you’ll have to clear the fuel lines of air before starting the engine again.

2. Stale fuel

Even when the lawn mower has enough fuel, it might be stale. Stale fuel is that which has stayed in the tank or container for about a month for ethanol-based, and about 3 months for other fuels. The fuel absorbs water from the air reducing its ability to combust properly.

Solution

If the fuel is stale, you should drain the gas from the lawn mower tank and replace it with fresh fuel.

If you’ll not be using the mower for a month or longer, either use up all the fuel or add a fuel stabilizer into the tank. Fuel stabilizers reduce the likelihood of the fuel absorbing water from the air.

3. Low oil levels

Oil serves both as a lubricant and a coolant for mowers. Without it in enough amounts, running the engine increases the chance of damaging the engine. For this reason, mowers and most other machines come with an oil gauge which prevents the running of the engine whenever the level of oil drops below a certain amount.

For this issue, wait for the engine to cool down so that the oil can settle then check for the level of oil in the engine using a dip stick.

Solution

Top up the engine oil up to the stated level before restarting the engine. Ideally, engine oil should be changed on regular basis as recommended in the owner’s manual. Draining of used oil from your mower is done before adding a new one.

4. Closed gas valve

Some lawn mowers have gas valves controlling the flow of fuel to the carburetor. Before starting the engine, the valve needs to be open to allow the flow of fuel first to the carburetor then to the combustion chamber.

Solution

Open the fuel valve by moving the lever to the OPEN setting the start the engine. Also inspect of there is any dirt or clogging that is preventing flow of fuel in an open valve.

5. Clogged air filter

Air filters, found on most combustion engines, filter the air before it mixes up with the fuel for combustion. They capture particles of different types and sizes and with time, clog up with the dirt. This reduces the amount of air reaching the combustion chamber.

Solution

Remove and clean the lawn mower air filter using a soft brush. If parts of the filter are worn out or broken, you should replace them or the whole filter.

6. Low battery

If the mower has an electric starter, it needs a battery with enough power to provide a spark to the spark plug. If the spark provided is too weak, the engine will crank weakly but won’t start up. If you use a pull cord to start the mower, this won’t matter as you don’t need power in the battery for that.

Solution

Charge the lawn mower battery using a different source then start the engine, or jump-start the mower with another battery.

7. Disconnected plug wire

The plug wire delivers electric power to the spark plug to enable the sparking for the starting and running of the engine. If the wire is disconnected, you won’t get a start. This usually occurs as a result of the engine vibrations as the wire is simply pushed into the side of the engine.

Solution

Simply push the spark plug wire back into the side of the engine to get a firmer connection.

8. Lock out features

Most engines including vehicles, generators, tractors and mowers have some safety features only known to the owner. These keep the engine from starting if in the wrong hands. If you’re unfamiliar with these features on your mower, ask the manufacturer or someone who used it before.

Solution

Change the lock out features to allow the engine to start.

9. Choke in the wrong setting

Whether your mower has a manual or automatic choke, if it’s not in the right setting, it’ll not start. It’s usually a lever on the side of the mower.

Solution

Move the choke to the FULL setting then start the engine again.

10. Spark plug problems

The spark plug delivers a spark to the combustion chamber to ignite the mixture of air and fuel. The spark plug is quite sensitive to the conditions inside the combustion chamber and won’t spark correctly if they’re not right. Some of the issues include:

  • Black and sooty plug: This is usually due to too much engine oil or a blown plug.
  • Wet plug: There’s too much fuel reaching the combustion chamber to spark properly.
  • Dry plug: Too little fuel in the combustion chamber. It can be due to a closed fuel valve or closed choke.
  • Wrong plug thread: The plug is either too tight or too loose.

Solution

If the plug is blown, replace it with a similar one. For too much or too little fuel in the combustion chamber, adjust accordingly. Use the correct plug thread as indicated in the mower’s manual.

11. Faulty control modules

Control modules are a set of relays and resistors that execute the commands from the sensors in your mower. They’re quite sensitive to moisture especially if the mower is usually left in the rain or in other wet conditions. Some mowers don’t have these modules and rely entirely on the ignition switch.

Solution

This one will need the input of an expert on the electronics of your mower. You can find one locally or call for one from the mower’s manufacturer.

12. Faulty ignition coil

The ignition coil is what creates the spark that ignites the air/fuel mixture in the combustion chamber. Given the hot conditions above the piston, coils have a high level of failure.

Solution

A faulty ignition coil can only be fixed by replacing it with a similar kind.

13. Malfunctioning carburetor

The carburetor has the role of mixing fuel with air then delivering it to the combustion chamber for ignition. Any malfunction from this part of the engine means that the whole combustion process is tampered with. You should have it checked occasionally to ensure it’s integrity.

Solution

If one part of the carburetor is missing or broken, you can have it replaced. If the whole carburetor is faulty, replace the whole unit. Sometimes a solution can be found in cleaning the lawn mower’s carburetor to remove dirty causing a clog.

14. Faulty ignition switch

The ignition switch is used on mowers that don’t rely entirely on a pull cord to start. It has terminals which can corrode making it faulty. It can also be an issue with the switch itself in that it doesn’t complete the circuit delivered to it.

Solution

Check the input, output and physical appearance of the switch. A digital volt meter can also help with this process. Fix the faulty parts and if it’s the switch itself at fault, replace it.

15. Faulty alternator

If you find yourself with a discharged battery even after running the engine for a while, it means that the battery isn’t charging accordingly. The charging is the role of the alternator and not charging means the latter is faulty.

Solution

While the engine is still running, check the DC voltage of the battery. If it reads less than 13 volts, the alternator is faulty and you need to replace it.

Final Thought

You need a working lawn mower to keep your lawns neat. Like any other machine, we cannot rule out chances of problems that will impair proper functioning of your mower. Fortunately, a faulty lawn mower can be inspected and be fixed as explained in this guide.

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