Flooded Lawnmower Lets Show You How To Fix It Yourself Fast.

What Causes Flooded Lawnmower and How To Fix It?

Flooded Lawn Mower

You’ve got a flooded lawnmower and need to fix it. We know how frustrating that can be, so we created this article to help you out. It’s full of tips and tricks for fixing your machine when your Lawn Mower Starts Then Dies or it won’t start or is flooding.

flooded lawnmowerIt’s a weekend and your day for mowing your grass has finally arrived. You have prepared everything – trash bags for the cut grass, a rake for gathering up the cut grass and a pitcher of cold water. You took out your old, reliable lawn mower from the garage and tried to start the engine. It won’t start. You turn the gas supply on, give it some choke and tug the pull start  rope repeatedly and the engine still won’t start. And after minutes of excruciating rope pulling, you smell gasoline coming out from the carburetor. Well, my friend, you now have a flooded lawnmower on your hands.   

A flooded lawnmower can be a problem for many beginners who own their first grass-cutting machines. But for more experienced homeowners with lawns, this is just a very common problem among lawn mowers.  

Today, we are giving tips on how to tell if your lawnmower is flooded, what causes a lawn mower to flood, and how to start a flooded lawnmower. And for those who are not familiar with the effect of a flooded lawnmower on a spark plug, we’re here to answer the question that many people are asking us – can flooding engine ruin spark plugs. 

How a lawn mower gets flooded is an excess of fuel in the carburetor that goes to the spark plug. This can affect its performance. Spark plugs play the most important role in the combustion of fuel to air mixture to get the engine up and running. 

How to Tell if Your Lawnmower is Flooded

how to start a flooded lawnmower There are three basic signs to tell if your lawnmower is flooded. Nonetheless, you must remember that flooding in a lawn mower begins with  the carburetor which supplies the fuel into the ignition chamber. 

✔️ First, it experiences hard starting. Even if you tug its start cord repeatedly the engine just won’t give in and start. And sometimes if the engine starts, white smoke may come out from the exhaust indicating a rich mixture which means the gas entering the combustion chamber is more than the combustion chamber can handle . Compared to the amount of air that’s entering the chamber. In this event, the engine may usually sputter or constantly die and this can also be called flooding of the engine. 

flooded lawnmower
✔️ The second sign of a flooded and it  is the fuel will leak out over the top of the carburetor or will run out of the throttle shaft or from the vent tube. So how could fuel overflow in a carburetor? The most common cause of this is the float needle valve inside the carburetor that controls the inflow of the fuel gets stuck. lawnmower is obvious

what causes a lawn mower to flood ✔️ The third symptom of a flooded lawnmower is the noticeable strong smell of gasoline. Once the gasoline leaks out due to the overflowing fuel in the carburetor, the strong odor of gas will emanate right from the carburetor. Especially if you continue to pull the starter cord and the engine won’t start then you smell the characteristic smell of gas, this means the fuel is filling up the carburetor beyond its optimum capacity.

So what causes the carburetor to overflow with fuel? First, let us tell you how the carburetors on lawn mowers work in a short explanation.

The carburetor is the part of an engine where the fuel and air mixture happens. The fuel from the tank enters the carburetor through the fuel supply inlet and then the fuel will go to the carburetor’s reservoir or bowl. Once the bowl is filled with fuel, the float valve will rise up and will push the jet needle up, sealing the tube of the fuel supply inlet so that no fuel will flow in.  

But once the fuel in the reservoir is reduced, the float will go down again and will release the needle so a new supply of fuel can come in.       

How does flooding in the carburetor happen? There are few reasons but the common ones are the following: 

↗️ The carburetor float gets jammed up due to its age or due to dirt that may have been trapped inside the carburetor and not allowing the plastic float to float so no sealing of the fuel supply inlet can happen.  

↗️ Some dirt may have been trapped into the mouth of the fuel supply inlet and the jet needle cannot fully seal the opening and allows the fuel to continuously flow into the carburetor’s fuel bowl.   

↗️ The tip of the jet needle which is normally made of rubber has worn out so gas can continue to come in even though the jet needle is seated its proper place.

↗️These scenarios are how the flooding of the carburetor can happen which is different from engine flooding.

What Causes a Lawn Mower to Flood and Fixing the Problem

A flooded lawnmower would not simply happen on its own without something causing it and sometimes it’s you who can cause the issues while it could be the lack of maintenance on your part. So what causes a lawn mower to flood, here are the most common causes and the best solutions you could try:   

Over choking.

how to start a flooded lawnmower  You left the “choke” fully engaged while pulling the cord many times when starting the engine and the ignition chamber became flooded with gas. Don’t forget that when the choke is open, more gas will flow from the carburetor more than what the engine needs to start and leaving the choke fully open while the engine has already started, will cause flooding.   


 Shut off the choke as soon as the engine starts and continue running. Some experts also recommend that whenever flooding occurs in the carburetor, leaving the machine for 15 minutes will let the accumulated gas dissipate and drain from the carburetor and from the ignition chamber. But if you don’t want to wait that long, you can repeatedly pull the  start cord to quickly dissipate the excess fuel then remove the air filter and clean it so that there is a clearer passage of air into the carburetor which will help in evaporating the trapped gas.  

Removing the spark plug will also help in ventilating the combustion chamber then recap the spark plug again after 5 minutes. While the air filter is removed, start the mower with the choke turned off.  If it starts, turn it off and put the air filter back then restart the engine.   

Lawn mower with a tank full of gas.

how to start a flooded lawnmower An engine full of gas that has been stored in the garage for a long time can make excess  gas seep into the carburetor and cause a flooded lawnmower. 


 Drain out the old fuel and remove the spark plug to see if its chamber is also flooded with gas. Keep the gas tank open and let all the remaining gas in the tank and spark plug chamber disperses. This will take around 15 to 20 minutes. Put a good amount of gasoline into the Lank and screw the spark plug back in. 

Clogged air filter.

If the air filter is clogged, it won’t take the right amount of air needed for the right air-fuel mixture. So while the gas is supplied in the carburetor, the flow of air is insufficient thus no successful combustion can occur inside the combustion chamber and flooding happens.  


flooded lawnmowerRemove the air filter. If this is dirty, clean, or better yet replace it. Squirt a little bit of starting fluid on the air intake port. Start the engine while the choke is in the off position. Once the engine starts, the excess fuel in the carburetor can easily burn out and you may see white smoke billowing for a few seconds. Once smoke is gone, turn off the machine and put back the air filter. 

Defective spark plug.

can flooding engine ruin spark plugs Check the spark plug if it is rusted or dirty, there could be spark misses during starting which allows the fuel mixture to fill the piston chamber and then go back to the carburetor. This is one of the reasons for a flooded lawnmower.


 Let the machine settle for about 15 minutes and while waiting, check if there’s gasoline in the spark plug seat, wipe this off and let the rest disperse into the air. After 15 minutes, recap the spark plug and start the engine. Change the spark plug altogether if it experiences spark misses again.

Blocked carburetor injector.

how to tell if your lawnmower is flooded When the carburetor’s fuel injector is blocked due to dirt or sludge, this will trap the gas that is inside the carburetor. And as more gas gets pumped in, your machine will become flooded.


The only thing to fix this is to disassemble the carburetor and clean its tubing and chamber with a carburetor cleaner. 

Stuck or worn float valve.

What Causes Flooded Lawnmower Another concern you must check is the float valve in the carburetor that could be worn out or has got stuck. When the carburetor gets old, this happens as the float valve begins to deteriorate. Or if the gasoline is left inside the carburetor for a long time and it begins to gum it up, this can make the float valve stuck. Remember that the float valve is what pushes the needle valve that stops the inflow of gasoline. 


There are repair kits you can buy to replace the removable parts of carburetors. Clean the inside of the carburetor before replacing these parts, or replace the carburetor if it’s worn out  to make sure a flooded lawnmower is no longer an issue.  

How to restart lawnmower when flooded, (  The quickest way ) you have to do some xtra measures and most of the time these steps would work. All you need is a spark plug wrench, dry cloth, screwdriver, and starter fluid. So here’s what you should do – 

How to Start a Flooded a Lawn Mower

If you’re a beginner in dealing with carburetor issues such as flooding, you may feel stressed out because you won’t know what to do about how to start a flooded lawn mower. However, there are quick fixes.

✔️ If you see the symptoms of a flooded lawn mower such as fuel leaks and the smell of gasoline coming from the carburetor, close the valve that delivers fuel to the carburetor to stop the flow. Pull the start cord as many times as you can until the fuel that’s left in the carburetor is vented out. During this time, the engine may start. Then open the valve and observe for any leaks. 

✔️ If there is still a gas leak, take off the carburetor and check its parts including the needle valve, the float valve and other small parts that are causing the overflow and check everything is clean. It could be the float valve or needle valve. Spray carb cleaner on all parts of the carburetor including the openings then assemble and reattach the carburetor. If it is still leaking, you might have to replace the carburetor with a new one.

✔️ Check the spark plug by unscrewing  it from its seat using a plug wrench. Usually, fuel and oil gets deposited on the spark plugs electrodes preventing the flow of electricity coming from the engine. So the best thing to do is unplug the spark plug, clean out its seat by inserting a clean white cloth to absorb the oil and fuel mixture.

✔️ Wipe the spark plug’s terminal and side electrode with the clean rag and make sure the electrode is not corroded or wet with gas and oil. If it is corroded, insert sandpaper in the electrode gap and eliminate the corrosion.

Can Flooding Engine Ruin Spark Plugs

What Causes Flooded Lawnmower and How To Fix It?Since we mentioned the spark plug which plays a major role in the burning of fuel, we should also understand more about it and how it can be affected in the case of a flooded lawn mower. So let’s answer the question – can flooding engine ruin spark plugs. 

Basically, when there is an excess of fuel or flooding in the engine this normally soaks the spark plug making it incapable of producing the right amount of spark to start up the engine.  But in most cases, when a spark plug is soaked, you need to replace it because eventually, this will show some signs of issues which can be any of the following: 

✔️ Knocking or pinging or rattling noises because of misfire. The sound may come from the pistons that rattle because of a misfire and the lack of combustion on the engine. 

✔️ Hard starting. A flooded lawnmower with a fuel soaked  spark plug will usually become hard to start  and if it starts, there will be a great reduction in the engine’s performance. 

✔️ Reduced acceleration. Due to the lack of electricity because of a problematic spark plug, acceleration can be noticeably reduced. 

Rough idling. This means that during idle or when the lawn mower is stationary, the engine can shake or rattle because the combustion in the engine’s cylinder is not constant. 

flooded lawn mowerWhat happens when you have a case of a flooded lawnmower and also a flooded spark plug, once the end or the terminal of the spark plug gets overly wet because the gasoline has entered the cylinder, the fuel can foul up the plug and will cause problems such as the ones we mentioned above.      

On the other hand, it doesn’t always mean that you have to replace the spark plug once it gets excessively wet with fuel. You may still want to clean it, dry it. Then try the spark plug again. Sometimes you only need to wait until the fuel on it evaporates for it to work again. 

Unflood a Flooded Lawnmower in a Conventional Way

flooded lawn mower Pull out the spark plug cap and using your spark plug wrench, unscrew the plug. 

✔️ Check the terminals if they are wet with gas and clean out the gas from the spark plug seat using a screwdriver wrapped in cloth. 

✔️ Spray the terminal (both end and top terminal) with alcohol-based starter fluid. If you don’t have this liquid, use the cloth to clean out the terminals.

✔️ Without the spark plug, crank the cord about five times to force air into the carburetor to dissipate the accumulated gasoline. 

✔️ Put back the spark plug, turn the choke to “off” and pull the cord again to start. Normally, the engine will sputter. Crank the engine more until the engine starts. 

✔️ If the engine doesn’t start, turn the choke on and crank again. Once the engine starts, quickly switch off the choke, turn off the engine and start the engine once more. 

✔️ Crank the engine and if there is no response, take off the air filter completely and crank . If the engine starts and sputters, this means the air filter is dirty or worn out and must be replaced with a new one. 

Important Tips to Remember

Usually, the best tips we can give you to avoid a flooded lawnmower is by taking out the spark plug and air filter and replacing them to ensure they won’t fail. An efficient air filter will protect your carburetor’s air intake more efficiently saving you more money from future repairs. 

Starting fluid can also be of great help especially during winter or if you have a flooded lawnmower. It is used generally for internal combustion engines and sprayed into the carburetor or near the air filter or on the spark plug and can act as a starting fuel. 

Because it contains highly volatile liquid it can also aid in disintegrating dirt that accumulates on parts where combustion happens. However, this is also highly flammable so be aware of your surroundings when you use it. 

As a last note, to avoid further problems, it is very important that you maintain your lawn mower. By keeping the mower clean, you can prevent problems from popping up especially when you need your mower most. Use an engine cleaner when cleaning your engine


The next time you have a case of a flooded lawnmower, don’t worry much about it. Just follow our tips here and these could guide in solving the issue. The only thing that you must be aware of is when your lawn mower’s engine already shows signs of ageing,  you may need help from a professional.