If your lawn mower keeps stalling, it could be down to a problem with the fuel pump. Also, stalling and sputtering are two telltale signs your fuel pump is on its way out. For example, if the fuel pump is damaged and it can’t get enough fuel to the carburetor, then you’re definitely going to notice a problem with your mower’s engine.
If you’ve got an engine that won’t start, then it could be a sign of a totally dead fuel pump. So, if you’re experiencing symptoms like these, then let me help you diagnose if the fuel pump is not working and then go over how to carry out the necessary repairs. Let’s take a look at the diagnosis first.
How to Tell If My Lawn Mower Fuel Pump is Bad? (The Short Answer)
Disconnect the outflow fuel line from the fuel pump that goes to the carburetor, then start your lawn mower engine. There should be enough fuel in the fuel line and the carburetor to allow the engine to run for about a minute. While the engine is running, check that there is a strong and continuous flow of gasoline from the outflow of the fuel pump.
What May Have Caused Your Mower’s Fuel Pump to Stop Working?
If your lawn mower doesn’t have a strong and continuous fuel flow from the fuel pump once it is disconnected and with the engine running, you’ll need to run a few inspections. Before swapping out the fuel pump, you’ll need to check a few components that could restrict fuel flow. Let’s take a look.
Clogged Fuel Tank Outlet
Inside the gas tank, you’ll find the fuel outlet. Unfortunately, it is very common for this outlet to get blocked up with debris like old grass clippings. So, pop off the gas cap and take a quick look.
Blocked Fuel Lines
The fuel lines could be the next item in the fuel system causing the issue. These can also get blocked up with debris that makes its way into the gas tank through the outlet. So, you’ll need to remove the fuel line and check if they are blocked.
The way to do this is to disconnect the fuel lines and see if gas flows through them with the aid of gravity. You can poke a wire through the fuel line if that doesn’t work. I find that a piece of electrical wire works well to push and blockage out of the lines once they are removed from my lawn mower.
Clogged Fuel Filter
The next item to check is the fuel filter. If the fuel filter is doing its job properly, then it should be collecting anything that makes its way through the fuel system and stopping it from entering the fuel pump and the carburetor. But the more debris it collects, the harder it will be for the fuel to pass through the fuel system. So, check the fuel filter and see if it is either clogged or very discolored. Usually, as a filter gets older and collects impurities, it starts to look dirty.
An Issue with the Incoming Pressure
A fuel pump works by receiving pressure from the engine via the crankcase through a rubber hose. If you look at your lawn mower, you’ll probably find a cover labeled OHV (Over Head Valve). Coming out of this cover, you’ll find a rubber hose that looks like a fuel line that connects to the fuel pump. This is where the air pressure travels to the pump to work the diaphragm.
So, before tackling the fuel pump, make sure that this hose is correctly connected and isn’t damaged. If you find a split in the pipe or that it’s not connected to the engine or the fuel pump correctly, you could be losing pressure causing the fuel pump to not work.
A Problem with the Fuel Pump
If you have checked all of the components that lead to the fuel pump and everything is working as it should, then it’s time to take a look at the fuel pump itself. There are a few things in the fuel pump that can go wrong and could need to be replaced. Let’s go over what these are.
A Closer Look at the Fuel Pump
Ok, now that you have confirmed that nothing else in the fuel system is causing the pump to act up, it’s time to go over some of the common problems with the fuel pump itself. So next, I will review some of the issues and the signs indicating your lawn mower fuel pump needs to be fixed.
Junk in the Fuel Pump
A common problem with lawn mower fuel pumps is that junk works its way into the pump and stops the diaphragm from working. Usually, the fuel filter will catch all the junk like grass clippings or other debris, but sometimes some dirt can work its way into the pump and create a problem.
A Worn or Damaged Diaphragm
Inside your fuel pump, there is a small rubber diaphragm activated by the incoming pressure from the crankcase. Now, this small piece of rubber has to continuously move back and forth while the engine is running to feed gasoline. You can imagine that this little rubber diaphragm will only last so long before it either hardens due to the constant contact with the gas or splits from the continuous movement. Either way, once it is damaged, it will no longer work efficiently or work at all.
Damage to the fuel Pump Housing
So the fuel pump is an airtight component on your lawn mower. This means that if it’s cracked or damaged in any way, air could escape and affect the pressure from the OHV. Usually, the fuel pump is tucked out of the way, so it’s pretty well protected, but if you are like me and a bit clumsy sometimes, you can easily damage the pump. So, if there is a noticeable air or fuel leak in the fuel pump, you’ll need to order a lawn mower fuel pump replacement.
How to Replace a Lawn Mower Fuel Pump (Step By Step)
Unfortunately, lawn mower fuel pumps are usually sealed units and can’t be repaired. So if there is a crack or you suspect a problem with the diaphragm, you’ll need to replace the entire fuel pump. Thankfully a replacement vacuum fuel pump is inexpensive and easy to get your hands on. It should run around $10-$20 and can be found online or at your local lawn mower store.
So, once you have your new pump, it’s time to go over the steps you’ll need to follow to successfully repair. So, let’s look at how you can replace your lawn mower fuel pump that’s not working.
Steps to Replace a Lawn Mower Fuel Pump
- Switch Off the Fuel
- Remove the Fuel IN Line
- Remove the Fuel OUT Line
- Remove the Vacuum IN Line
- Remove the Fuel Pump Mounting Bolts
- Remove the Old Fuel Pump
- Mount the New Fuel Pump
- Install the Mounting Bolts
- Connect the Vacuum Line
- Connect the Fuel IN Line
- Connect the Fuel OUT Line
- Switch the Fuel On
- Test Your Lawn Mower
Switch Off the Fuel
The first job is to switch off the fuel on your lawn mower. This can be done using the fuel cut-off valve if your lawn mower has one. If your lawn mower doesn’t have a cut-off valve, you can use a fuel line clamp on the fuel line anywhere between the fuel tank and the fuel pump. This will stop gasoline from leaking from the gas tank once the fuel lines are removed.
Remove the Fuel IN Line
The next step is to remove the fuel line that connects to the fuel pump on the IN connection. This is the fuel line that comes from the fuel filter. So, take a pair of pliers and pinch the spring clip that holds the fuel line tight to the fuel pump, then slide the clip a few inches down the fuel line.
Remove the Fuel OUT Line
Now, use your pliers to slide the spring clip on the outflow pipe a few inches down the pipe. This is the pipe that connects the fuel pump to the carburetor.
Remove the Vacuum IN Line
The final clip to move is the clip on the line between the OHV and the fuel pump. Again, use your pliers and move the clip an inch or two down the line and out of the way.
Remove the Fuel Pump Mounting Bolts
Usually, a fuel pump is held to the lawn mower engine with two bolts. So, grab a socket wrench, remove these two bolts, and set them aside for later.
Remove the Old Fuel Pump
Once all the pipes and bolts are removed, the old fuel pump should just lift off the lawn mower. So, once you have it free from your lawn mower, you can throw it in the trash.
Mount the New Fuel Pump
Now, it’s time to install the new fuel pump. So, place your new fuel pump onto your lawn mower’s engine. The fuel pump can be installed in two ways. One is right, and one is wrong. To do it right, note where the fuel pump connections are facing. You want the outlet to face the carburetor, the inlet to face the fuel filter, and the vacuum line to face in the right direction to connect the hose from the OHV.
Install the Mounting Bolts
Once you have the new fuel pump positioned on your lawn mower correctly, you can go ahead and install the two bolts that you previously removed. Now there isn’t any specific torque setting that you need to reinstall the two bolts but just be careful not to do them up too tight. I learned this the hard way. I over-tightened the bolt and cracked my new fuel filter before finishing the repair. Luckily they are not too expensive.
Connect the Vacuum Line, Fuel In Line & Fuel Out Line
The next step is reconnecting the three hoses you removed from the old fuel pumps. So, slide each hose onto the new fuel pump as far as they go, then reposition the three spring clips using your pliers.
Switch the Fuel On & Test Your Lawn Mower
The last thing to do is switch the fuel back on by either turning the fuel cut-off valve back on or removing the fuel line clamp, then fire up your lawn mower. Because you have been working on the fuel system, the system is out of air. So, you’ll probably have to turn the key a few times to get the engine started.
Be patient when bleeding the fuel system, but rest assured the lawn mower will take care of the process without you needing to do anything extra.
Tools & Parts Needed if Your Lawn Mower Fuel Pump is Not Working
- Fuel Line Clamp
- Pliers
- Socket Wrench Set
- Replacement Fuel Pump
How to Extend the Life of Your New Fuel Pump
The only thing you can really do to extend the life of your lawn mower’s fuel pump is to make sure you regularly swap out your fuel filter and keep an eye on your fuel lines. In addition, you want to make sure that the fuel getting to the fuel pump is always nice and clean. This means keeping junk out of the fuel tanks and carrying out regular maintenance.
Oh, and try not to let anything come into contact with the fuel pump. Clumsy me backed into a tree branch and cracked the fuel pump. Thankfully, my mower was back up and mowing after $15 and thirty minutes of my time.
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