Ideally, when heading out to the yard with the mower, you only have to start the lawn mower once, and off you go. But, unfortunately, there are moments when you’ll find yourself having to repeatedly strike up the engine because the lawn mower sputters and dies. If you’re lucky, you’ll manage to keep the engine running, but it will keep on sputtering, making cutting the yard hard work. So, let’s take a look at what could be going on here.
Fixing a Lawn Mower That’s Sputtering (The Short Answer)
The sputtering of a lawn mower’s engine is a sign that there isn’t enough fuel making its way to the cylinder head for ignition. There are several engine components in the fuel’s path that play a vital role in getting the gasoline from the fuel tank to the combustion chamber. A problem with any of these components can cause the engine to sputter.
6 Possible Reasons Why Your Mower is Sputtering
Instead of struggling with your lawn mower sputtering, here are six different parts of your mower’s engine that are more than likely causing you the issue. Let’s take a closer look at what these parts are and how you can diagnose if they are the root of the problem.
- Fuel Filter
- Fuel Line
- Fuel Pump
- Carburetor
- Gas Cap
- Bad Gas
Lawn Mower Sputtering Caused by the Fuel Filter
Fuel filters are serviceable parts that need to be changed every so often. They filter imperfections and debris out of the fuel and prevent damaging material from reaching the more delicate parts of the engine. As a result, they become clogged and reduce the flow of fuel. Even if you keep trash out of the fuel tank, you will not be able to keep the imperfections out.
So, locate the fuel filter on your lawn mower and check how it looks. Ride-on lawn mowers, like John Deere’s and Husqvarna’s, usually have transparent filters making it easy to see if they have discolored. But smaller walk-behind mowers, like Toro’s and Troy Bilt’s, have fuel filters that you can’t see into. This means all you can do is replace it.
So, if it’s been a while since you have replaced the fuel filter, or you never have, then I’d recommend you swap it out. This is something I do at least once every year.
Fuel Lines Making your Lawn Mower Sputter While Running
Fuel lines are like the arteries of a lawn mower. They carry the gas between the different components of the fuel system. If they become clogged with debris or fuel gum, then they narrow and reduce the flow of fuel. As a result, you’ll need to disconnect the lines and either clean them or swap them out.
So, remove your fuel lines and see if there are any blockages. I find the best way to do this is to remove one end of the fuel line (furthest end from the fuel tank) and check to see if the fuel flows through it. If you only get a drip through the line, then you’ll know there is a problem.
Lawn Mower Sputters and Dies Due to the Fuel Pump
Fuel pumps are a little more difficult to diagnose. They rely on a small diaphragm and pressure created by the engine that only works while the engine is turning over or running. So, you’ll need to inspect how the fuel flows through the pump.
To do this, remove the outflow fuel line from the fuel pump and turn over the engine. There should be an unimpeded flow of fuel that flows with consistency. If the flow is random or slow, you could have found the cause of why your lawn mower sputters but runs. Just be sure to have a container to catch the gas.
Carburetor Leading to a Sputtering Lawn Mower
To check if the carburetor is the reason why your lawn mower sputters while running, you’ll need to pull it apart and see if it is operating correctly.
Inside the carburetor there are several components that work together to turn liquid gasoline into a vapor. Parts such as the jet and float can become clogged and jammed, causing an issue with the flow of fuel and vaporizing process.
So, you’ll need to grab your tools and remove the carb from the lawn mower. Once you have the carb off the lawn mower, you’ll want to inspect the jet. In my experience, the most common issue with carburetors is a blocked jet.
Lawn Mower Sputters but Runs Because of the Gas Cap
The gas cap keeps fuel in the tank and trash out, and it also plays a part in regulating the pressure in the tank. To do this, the gas cap has a vent that can become blocked or obstructed.
As a result, a gas cap that is not venting will create a vacuum and prevent the gas from flowing through the fuel system. So, remove your gas cap and take a look at the vent. If you can see that it is blocked or obstructed, say from some kind of damage or dirt, you’ll know that the cause of the lawn mower sputtering could be due to a vacuum in the tank.
Bad Gas Results in a Sputtering Lawn Mower
Bad gas can cause a number of issues with your lawn mower, including sputtering. As gasoline goes bad, it forms a varnish – a sticky gum-like substance. As the bad gas flows through the fuel system, it damages the components and creates blockages. The bad gas that reaches the cylinder head for combustion cannot ignite the same as good, fresh gas. The result is a sputtering lawn mower.
The easiest way to check if your fuel has gone bad is to carry out a visual inspection. If you remove some fuel from the lawn mower and compare it to fresh gas, you will hopefully find that it is the same color. If the gas in the lawn mower turns out to be a darker brown or yellow color, then you’ll have discovered there’s bad gas that will need to be removed.
How to Fix a Lawn Mower That Sputters
So, if you have been through the six potential causes for your lawn mower sputtering and found that you have a problem, then you’re going to have to carry out a fix. Here’s what you can do to solve the issue.
Replacing a Fuel Filter
The first thing you’re going to have to do to replace your fuel filter is to get a new filter specific to your lawn mower. Getting the wrong filter can cause flow and performance issues like sputtering of the engine.
So, once you have your new filter, you’ll need to remove the fuel line clips and fuel lines from the old filter. A pair of pliers should work fine for this. Next, take your new filter and attach the fuel lines and replace the clips. During the installation, make sure that you install the new filter in the correct orientation. You’ll find an arrow on the side of the filter showing you the direction of the fuel flow.
Tools & Parts
- New Fuel Filter
- Pliers
Installing New Fuel Lines
Installing replacement fuel lines is pretty much the same as replacing a fuel filter. This time, you need to remove both ends of the fuel lines and make sure you remove all the lines. You‘ll find fuel lines located between the fuel tank and fuel filter, the fuel filter and the fuel pump, then between the fuel pump and the carburetor. This can vary between mowers.
Then, follow the same process of removing the lines from the fuel system components, including the clips using your pliers. Next, cut a length of new fuel lines to match the original lines and install them on the mower and replace the clips.
Tools & Parts
- New Fuel Lines
- Pliers
- Cutters
Replacing a Fuel Pump
Fuel pumps come in all shapes and sizes, so there isn’t one set of instructions for all types. But as a general guide, you need to remove the connecting lines and then remove the defective pump.
So, located on the pump are a number of lines. The fuel inflow, the fuel outflow, and in some cases, an air pipe from the overhead valve. As long as you install the pipes in the same locations on the new pump, you shouldn’t have any problems. Again, you’ll need your pliers to remove the lines and a small socket set or wrench set to remove the pump mounting bolts.
Once you have the old pump removed, you can mount the new pump and connect the various lines.
Tools & Parts
- New Fuel Pump
- Pliers
- Socket Wrench or Wrench Set
Replacing the Carburetor
If you are familiar with engines, then you’ll probably be comfortable pulling apart a carburetor. But for those of you that may not be so comfortable with this type of job, you can simply replace the carburetor. A new carburetor isn’t that expensive and should run you for less than fifty bucks. Again, there isn’t one set of instructions to replace a carburetor, so I’ll give you an overview of the general steps included.
First, you’ll need to remove the air filter and locate the mounting bolts/screws for the carburetor. Then, use the appropriate tools and remove the mounting bolts/screws, and set them to one side.
Next, take a pair of needle-nosed pliers and remove the connecting bars/pins from the throttle control and the governor. These connections are usually small metal bars/pins slotted through small holes in the carb. Once these are removed, the carburetor should be completely free of the engine.
Next, connect the accelerator and governor connections to your new carburetor. Then install the pair of gaskets that should have come with your new carburetor. One pair goes between the carb and the engine, and the other goes between the carb and the air filter. To make this stage easier, I like to use a little gasket sealer to hold the gaskets in place when installing a new carb.
So, position the gasket, carb, second gasket, then the air filter housing on the engine and install the fixing bolts/screws. This is where you need 4 hands. Once this is done, install the air filter and air filter cover, then reconnect the throttle and governor link, and you are done.
Tools & Parts
- New Carburetor
- Socket Wrench Set
- Screwdriver
- Needle Nose Pliers
- Gasket Seale
Cleaning a Gas Cap Blockage
A blocked gas cap can cause you a world of trouble, but thankfully they only take a few seconds to fix. Well, as long as it’s not damaged.
So, take a small wire or pin and poke it through the vent in the cap. That is all you need to do. If you happen to find a problem with the cap, like some damage, I’d suggest that you head out and pick up a replacement. If you happen to see a universal gas cap, make sure that it’s the right one for your mower.
Tools & Parts
- Wire or Pin
Removing Bad Gas
To remove bad gas from your lawn mower, you’ll need to get hold of either a fuel siphon or a fuel transfer pump. The basic principle to remove the bad gas is to remove it without having to use it. The last thing you want to do is continue to use the mower with the bad gas and increase the damage to the components of the fuel system.
So, the process is to either pump or siphon out the gas. If you don’t have these tools, you can remove one of the fuel lines, preferably the line between the fuel tank and the fuel filter, and drain the tank. Either way, just be careful when handling gasoline and take the necessary precautions.
Tools & Parts
- Siphon or Pump
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