Lawn Mower Is Not Starting - Common Causes & Fixes -

Lawn Mower Is Not Starting

Common Causes & Fixes

lawn mower is not starting

Lawn Mower is not Starting​

gas lawn mower won't startYou really have to look at your lawnmower if it’s not starting normally as it used to. If your lawn mower is not starting, this can be caused by many factors. Hard starting is one of the most common problems that we can encounter with our lawn mowers and sometimes even your  lawn mower starts then dies  in the middle of your lawn mowing job this also spells trouble. 

In this blog, we are going to discuss the most common causes of why a lawn mower does not start. Why a gas lawn mower won’t start that easily usually during the cold season.  The surrounding temperature can also play a big part not only in the performance of the engine but also with its starting process. On the other hand, there are also some typical causes why hard starting occurs.

5 Common Causes Why a Lawn Mower Does Not Start & Best Solutions

Lawn mower is hard to start –
Bad Gas in the Tank

gas lawn mower won't startYou know what they say about the fuel “old gas is bad gas”, that is basically true because gasoline can only be best 30 days after it is produced. So if gas in the tank of the lawnmowers is full during the off-season months, this can produce slime-like sediment and  once these get into the pipes can produce blockages, especially in the carburetor. When this happens, the movable parts of the carburetor may malfunction. The float valve and the needle valve which are responsible for controlling the flow of fuel pumped into the combustion chamber can get stuck. So sediment from old gas can ultimately block the fuel system and can also result in leaks on the carburetor due to flooding. 


If your problem is your lawnmower is hard to start or ultimately the lawnmower is not starting at all, this could mean that the dirt in the old gas is causing the blockages. Insufficient distribution of gas to the carburetor, flooding in the carburetor, and the improper mixture of air which can result in hard starting, engine stalling, and sputtering are some of the symptoms of blockage due to bad gas.  


lawn mower is hard to startWhen it comes to preventing future trouble, prevention is also better than cure. So if you don’t want the gas to form sludge during the off-season while it’s in your lawnmower’s tank, use a fuel stabilizer . Fuel stabilizer products can provide protective layers to the fuel while it can prevent the evaporation of gasoline and also stops it from producing sediment. These products can make the gas last longer while maintaining its quality. Remember that gasoline can only be good for about 30 days so beyond that, it can get stale slowly without stabilizers. However, if you don’t want to use a stabilizer, drain all the gas from the tank before storage for the winter and keep your lawnmower in a dry shaded place. 

There are two ways to drain out the gas from a lawn mower but make sure before you do these you should disengage the spark plug first. The first is by tilting the machine on the opposite side of the air filter to prevent it from getting saturated with gas. Remove the gas tank cap and tip the gas to a container. Second, use a hand siphon which is much safer and quicker. You only need to insert the first tube of the siphon into the tank down to the bottom and let the other tube hang into the container then pump the tool 3 or 4 times and the gas will automatically flow out through the hose.  

After draining all the gas out, keep the machine in your garage and when you’re about to use it, don’t forget to mix the gas with a fuel stabilizer and follow the right gas-stabilizer ratio written on the product’s label. Learn How to Winterize a Lawn Mower here

Bad Spark Plug  

lawn mower is hard to startThe spark plugs are like the igniters of lawnmowers. They produce the spark to ignite the fuel and air mixture inside the combustion chamber so that the pistons move and power up the engine. So if you have a bad or an old spark plug, most likely your gas lawn mower won’t start or the lawnmower starts then dies. 


Several signs could tell you if your lawnmower’s spark plug is bad. The first sign that you will notice is hard starting. Second, the lawnmower will start after much pulling then will die before it runs. And lastly, the engine may stall while running. To check the condition of the spark plug, undo it from its seat and check. Turn it anti clockwise to undo it ,but be careful not to cross thread it when reinstalling.  You may see some corrosion or carbon deposits or even oil and gas on its terminal. If this is the case, a replacement would be necessary. 


If the spark plug is still looking good but you see some dirt deposits on its electrode and terminal, wipe the dirt off with a clean rag including the seat of the spark plug. Make sure the electrode which is the top coil that produces the spark is completely cleaned out. Then insert fine sandpaper between the side electrode (hooked wire) and the center electrode and slowly sand them until you see the dirt cleared out. 

If you have a gap tool, measure the distance between the side and the center electrode and it should be at least .033 inches or 0.08 cm. Remember that too wide a gap, the electricity can not jump between the electrodes. And with a too narrow gap, the electrodes would not produce the spark. Spark plugs are designed for about 25 hours of use or longer for branded ones.

Clogged Carburetor

why won’t my lawnmower startAnother cause of why a lawn mower is not starting is due to clogged  carburetor as we have discussed above. How a carburetor can be clogged up from old gasoline’s sediments. Usually, what makes your gas cloudy is the ethanol it contains. Like we have said  gas shelf life is about 30 days and the ethanol it contains not only can produce sediment and blockages  but can also corrode soft metals. 

If the carburetor becomes flooded with gas because  the needle valve is partially blocked, the carburetor would not be able to produce the proper air-fuel mixture and the combustion in the combustion chamber may go haywire.  


You can see some signs of a flooded carburetor such as the smell of gasoline and see drips coming out from the carburetor while the smoke that will come out of the exhaust can be white smoke which tells you that your engine is having a richer mixture of gas than air. The engine may also sputter or stall.   


The best thing to do when a lawn mower does not start because its carburetor gets clogged is to drain out all the gas from the tank and disconnect it. Take the carb off your mower. Clean everything inside it including the small parts like the needle valve and the float valve including the inlet and outlet hoses where the fuel comes in and out.  

Use a carb cleaner to dissolve soft blockage inside of the carburetor and check also the nut that’s holding the carburetor cup found at the bottom of the carburetor. This nut also has a hole in it that regulates the air pressure inside the carburetor. 

Dirty Fuel Filter

People also ask us why a lawnmower is not starting when it has fresh gas and a new spark plug installed? So we asked them this question: did they check the fuel filter?  Yes, the fuel filter is one of the most overlooked parts of an engine but its main function is to filter the gas from the gas tank and it’s located along the fuel line or under the fuel tank of your lawn mower. If this filter gets clogged  with dirt from bad gas sediment, this can explain why a gas lawn mower won’t start. 


The most common symptoms of a clogged fuel filter can be sputtering of the engine when starting, hard starting, constant idling of the engine, lack of acceleration, or the lawn mower does not start even with strong and repeated pulling.  


The lawn mower’s fuel filters are made of 2 types: metallic and paper/nylon filters. For the metallic ones, you need to disengage them from the fuel line, drain the fuel from them and spray with carp cleaner thoroughly. Once the carb cleaner dries, blow on one end to eject any sediments that are inside it. But if the filter still looks dirty, replace it with a new one. With the paper/nylon filters, these are disposable so once they are clogged badly, you have to replace them.   

Dirty Air Filter

The use of air filters on lawn mowers is very essential because it cleans out the air that goes inside the combustion chamber to the engine. It traps dirt, debris, and other particles and prevents the engine from getting damaged. All lawnmowers need clean air to cool their system, especially gas-driven lawnmowers for their fuel combustion that is required to power the engines. Without the air filter, extreme damage to the engine can happen. 

Three main types of lawn mower air filters are: the foam filters, paper air filters, and dual filters that have paper and foam components. 


Because there will be a decrease of airflow to the engine due to a dirty or clogged air filter, the signs can include hard starting, engine stalling, sputtering, loss of power, and increased fuel consumption. There could also be black smoke that will come out from the exhaust. 


Air filters are generally easy to detach from their holders thus easy to know when they are clogged or damaged. To clean air filters, the foam types even if they get soaked with oil and debris can be cleaned under running water then apply detergent soap, lather them up by squeezing them, then rinse under running water again. But if the foam is worn out, better replace it.

With the dual and paper type air filters, once they get soaked with carbon and grease, better replace them altogether. But if only dry dust is clogging them , try brushing the dirt with a dry paintbrush or blow the dirt using an air compressor.  

Failing Starter Solenoid

lawn mower is hard to startMost of us don’t know what a starter solenoid is and its function on lawnmowers. A starter solenoid is a small magnetic device shaped like a small cylinder and found inside the starter motor. You will know that this is the solenoid when you see two red thick wires that connect to the battery and the other wire to the starter motor. Its function is to send current to the starter motor once you switch on the ignition on a riding lawn mower. So whenever you turn the key on the riding lawnmower’s ignition and there’s the clicking sound, that’s the starter solenoid doing its job. 


If you hear the click and the lawn mower is not starting, there could be a problem with the solenoid itself and it’s losing its connection and cannot send current to the starter motor. 


The best way to answer the question – why won’t my lawnmower start when I hear a clicking sound with my riding lawnmower but nothing happens, that issue could be a starter solenoid problem. And by replacing this part could solve the problem of your lawnmower not starting. This part could be expensive but it would cost you more if you take your machine to a repair shop. If you can,ask a mechanic friend about the problem with your riding lawnmower and if he tells you it’s a solenoid problem then you could buy this part and install it yourself. This will save you money on repairs.    

Now that you have learned some things about why a lawn mower is not starting, the next time your machine doesn’t want to start, just try some of our suggestions first before you take it to the repair shop.