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Gas Leaking From Primer Bulb On Lawn Mower – Here’s How to Fix

by Jack Grover
Reading time: 11 min Prefer to listen?

Why is gas leaking from primer bulb on lawn mower? Well, even though there are many reasons why primer may leak gas in lawnmowers but the most common issue is the carburetor not getting enough fuel. 

Apart from that, there are a few other issues as well which are often seen, and in this very guide, we will be taking you through the most common reasons why your lawnmower primer bulb might be leaking gas. 

Let’s get started!!!

Reasons for gas leaking from primer Bulb on Lawn mower

For a quick glance, we have prepared this table; check it out. 

Carburetor not getting enough fuelCheck for the dirty oil filter, faulty fuel pump and clogged fuel line
Damaged diaphragm Replacing the diaphragm
Stuck float valve in the carbReadjust and reseat it
Damaged Gasket or O- ringReplacing gasket or O-ring.

In lawnmowers, the leaking primer bulb is one of the most common issues. If you have worked with any, you know it. And it is tough to find out the reason if you aren’t an expert. 

However, as we have mentioned before, there are many reasons why a land mower primer bulb might leak gas, and here in this section, we will be looking into all of those common reasons why primer bulb leaks gas and how you can fix it.

Low Fuel Supply in the carburetor 

The primer bulb is what transfers fuel from the tank to the carburetor. And if you see the bulb is leaking gas, it is probably because of the low fuel supply to the carburetor. Most of the time, this is the reason that causes a gas leak. 

In case you don’t know, a carburetor uses a set amount of fuel and air to create a mixture that runs the engine. So if the carburetor doesn’t get the right amount of fuel, it is obvious that it wouldn’t be able to create the mixture, leading to a gas leak on the primer bulb. 

When the carburetor can’t make the mixture or makes an imperfect mixture, that leaks gas and damages the engine pretty badly.  

Now let’s talk about the reasons why the carburetor doesn’t get the proper amount of fuel. We have pointed out the 3 most common reasons for that. 

  • When the oil filter isn’t cleaned or replaced for a long time, the dirt build-up can block the normal flow of fuel. 
  • If the oil filter doesn’t work properly, that means it is not cleaning the oil. And that will result in dirt build-up in the oil lines resulting in clogs. And that limits the oil flow to the carburetor. 
  • The fuel pump draws oil from one place to another, so the oil flow will get interrupted if that doesn’t work fine. 

Fix the problem

The fix is very easy. You just find out what is limiting the gas flow to the carburetor and then fix that. For example, if you find out the oil filter is blocked, then clean it or replace it with a new one that should do the work. 

If the oil line is clogged, unclog the line with something thin and pointy. But if you have a faulty oil pump, that’s going to cost you a bit. You might need to change the oil pump.

Damaged Diaphragm 

The diaphragm also contributes to drawing or transferring fuel from the tank to the carburetor along with the primer bulb. The diaphragm in the carburetor is a rubbery material, and the constant exposure of fuel and air causes it to rot over time. 

But there are a few things that damage the diaphragm at an early age and the most common reason is dirty oil. And when the diaphragm rots or gets damaged, it gets hard and doesn’t function at all, leading gas leak on the primer bulb. 

The main symptom of having a damaged diaphragm is that the mower will refuse to start or shut down in the middle. 

Fix the problem 

Unfortunately, once the diaphragm gets hard, you cannot get it back to its normal state. That means you will have to replace that. It is slightly expensive too. 

Stuck float valve in carburetor

Sometimes it might happen that the float-valve in the mower carburetor is stuck, which is why the primer bulb is leaking gas.

Fix the problem 

In this case, fixing is super easy. You don’t have to toil much. In the carburetor, locate two nuts, among which one is at an angled position.

Loosen that nut, but don’t remove it. And keep it like that for a few minutes to let the fuel bleed out.

Finally, when there is no fuel left to bleed, retighten the nut and tap a few times on this float chamber of the carburetor. This will just reseat the floating valve and the entire chamber.

Damaged O-ring or gasket 

An O-ring or gasket is what seals the primer bulb so that it doesn’t leak gas. And if that gets damaged, then the primer bulb leaks gas. However, if the gas leak is due to the o-ring or gasket, then it is not something to worry about since it is easy to fix. 

Fix the Problem 

A gas leak due to a worn-out gasket or O-ring is super easy to fix and pretty light on the wallet as well. These come at an affordable price, and if you have a little bit of knowledge, you can do the changing by yourself. 

Apart from all that, if your primer bulb itself gets damaged, that can also lead to a gas leak. So, in that case, you should consider replacing the primer bulb on the lawnmower.

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Frequently Asked Questions (FAQs)

Why Is My Briggs and Stratton Leaking Gas?

Even though Briggs and Stratton engines are known for their top-notch durability and reliability, every engine develops problems with time. And so do these two. There could be a lot of reasons why your engines are leaking gas, it could be the primer bulb, carburetor, oil filter, motor pump, etc.

u003cstrongu003eShould Lawnmower Primer Bulb Have a Hole in It?u003c/strongu003e

Is primer bulb good with or without a hole in it, that’s a never-ending debate. Some say having a hole in it helps the engine start easily, other says, the hole might cause the engine to floor. So it is up to the people, if you like having a hole on the bulb, so be it.

What would cause a lawnmower to leak gas?

There are a few things that might cause gas leakage, which are

How Do You Bypass a primer bulb on a lawnmower?

You can disconnect the primer bulb from the engine. Or you can remove the gas cap to pour the gas directly into the carburetor. 


We hope now you know what to do if you see gas leaking from primer bulb on lawnmower. Apart from the reasons we have mentioned, there are some other less common reasons as well.

So if you are new to lawnmowers, it would be best to find a mechanic to diagnose the problem. That might cost you a little money, but it will be worth the penny.

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