When your lawn mower only runs with choke on, it is obviously not normal and can be an indication of an issue. The culprit in this occurrence is probably a problem with the fuel or the carburetor.

My Lawn Mower Need the Choke On to Run

Let us dive deep and discuss this topic to understand better the possible reasons why this is happening to the lawn mower and how you can fix this issue and prevent it once and for all.

Why Does Your Lawn Mower Only Run With Choke On?

Your lawn mower only runs with choke on because of a problem with the engine fuel-air mixture system, which can be caused by the carburetor, bad fuel, or air leaks. The choke compels more fuel in the combustion chamber to help the engine to turn over when cold.

A choke functions by decreasing the air supply, increasing the suction, and enhancing the air and gas mixture that goes into the engine. There are different possible reasons to consider when trying to identify why the lawn mower only runs with choke on.

There might be an underlying issue with any of the following: carburetor, air supply, and fuel. The lawn mower should be operated with the choke on for no longer than five minutes.

Allowing your lawn mower to operate with the choke on will give rise to several problems like irregularity in engine power performance and excessive consumption of fuel. This may eventually damage the engine, so to address this kind of lawn mower issue, let’s start to examine the possible causes and be prepared to fix them.

Let’s talk through these reasons one by one so you will be familiar about what to inspect and how to troubleshoot the lawn mower.

– Carburetor Problems

Clogging in the carburetor is the most usual problem that your lawn mower might be facing, which is why your mower runs only with choke on.

The carburetor can be easily clogged by rust or debris that are in the fuel because the carburetor has small jets inside with tiny holes in them to enable the gas delivery to reach the combustion chamber.

Another possibility to look at is when the carburetor gets gummed up because of occasional use. The air intake could dry out the gas in the carburetor, which results in a sticky substance, and over time, the gas that was left in stock for so long will coat the walls of your carburetor and build up.

This condition reduces the ability of your lawn mower carburetor to supply the correct ratio of air and fuel as its tiny parts cannot move properly. This would cause the lawn mower engine to only run with the choke on.

Moreover, the reason why your mower starts on choke then dies is because of debris that clogs, at least partially, the fuel passages in the carburetor. When this happens, the choke will provide the extra fuel needed to go into the engine and overcome the lack of fuel that enters through the other passages.

– Bad Fuel

Bad fuel can also cause your lawn mower to run only with the choke on. You may be using an incorrect kind of gas or old gas, especially if you haven’t used the lawn mower for a long period of time.

Reasons for Lawn Mower Only Runs With Choke On

You may also want to check whether the fuel has an excessive volume of alcohol. As every type of regular fuel is blended with at least ten percent of ethanol in the United States, it contains moisture that can cause your carburetor to rust and be gunked up.

Using the wrong fuel might also be the reason why your lawn mower, even after having a new carburetor, only runs on choke.

– Air Leaks

Air supply plays a significant role in the fuel delivery system. Many issues can be related to air supply. These issues include leaks or cracks that have developed in the carburetor areas like loose hardware or the primer bulb.

The wrong placement of the air screw of the carburetor that controls how much air mixes with the fuel, and a damaged or incorrectly set gasket are also some issues.The above issues may result in an excessive amount of air being delivered and a weak vacuum system.

This condition can cause the lawn mower to only run with the choke on. Having a dirty air filter also prevents the airflow from coming through as needed, so this condition should be attended to as well by cleaning your lawn mower’s air filter.

How Can You Fix Your Lawn Mower?

To fix your lawn mower that only runs with choke on, you can clean or change the carburetor, replace the fuel, or fix the air leaks. While there are lots of reasons why your lawn mower only runs with the choke on, here are several ways to fix it. Lawn mowers take regular gas and you should know how to refuel them properly.

Let’s begin to know each of the solutions and talk about the steps you can take to address the problem.

– Clean or Change the Carburetor

It is an important step to give your carburetor a good cleaning first before you decide to replace it to know whether it just needs a cleaning or if it truly needs replacing. By this time, you may want to observe its appearance.

If you see that it is extremely gummed up or rusted already, you may want to replace it instead of wasting your time cleaning it. Whichever you decide, you will need to detach and disassemble the carburetor first.

For cleaning, you may want to use a carb cleaner for the interior of the carburetor and jets for spraying the cleaner onto the component. However, if you see that your carburetor has plenty of gas residue, soak it for at least a couple of hours using a carburetor cleaner.

Make sure that you know how to assemble and install it again once you have finished cleaning it.

– Replace the Fuel

In the United States, regular fuel works great on large engines. Unfortunately, this is not the case on smaller engines, so make sure that your fuel does not have an excessive amount of alcohol to prevent your carburetor from deteriorating.

Opt for a lower percentage of non-alcohol blended gas, or take a shot at using a non-oxygenated or premium fuel instead. The wrong fuel might just mess with the internal combustion process of your engine.

Also, make sure that you throw away the fuel that has been sitting on your mower for more than a year. Try to observe the fuel’s color to easily identify if it has gone bad. Fuel that smells sour and has a darkened color has already gone bad and has to be thrown away.

Solution for Lawn Mower Only Runs With Choke On

Drain out all the fuel in your mower’s tank, and clean the sticky residue that is left behind before you replace it with fresh fuel. Keep in mind that you must clean the tank up before adding newer fuel, as leaving it dirty won’t solve anything.

– Fix the Air Leaks

Once you are certain that your lawn mower carburetor is having an issue with the supply of air, the first thing you can do is pinpoint the specific area where the supply of air is disrupted.

You can start to look for loose connections or any cracks, and inspect the primer bulb as well because it is made of rubber and can be brittle and get cracked as it ages. Examine the mounting gasket, and observe if something does not look right. Any edges that are bulging out or components that appear cracked or dried should be replaced.

Check the fuel cap as well, and ensure that its seal is still on and in good condition. Maintain the cleanliness of the air filter because the dirtier it is, the more issues may occur for your lawn mower. Check for gunk that has built up and is clogging the filter.

However, if you see that the appearance might be beyond cleaning, consider replacing it with a new one instead. Lastly, scan your carburetor and ensure that every piece of hardware is properly tightened and secured.

Causes of Lawn Mower Choke Issues


Though it seems difficult to determine the problem of your lawn mower that only runs with choke on, a bit of hard work, perseverance, and plenty of insights from this article will help you and your lawn mower work properly again.

  • A lawn mower that only runs with the choke on might be having problems with the carburetor, air supply, or bad fuel.
  • Maintaining a clean carburetor will make the fuel delivery system run smoothly.
  • Use high-quality fuel to extend the lawn mower’s life.
  • Make sure that there is no disruption to the air supply as it is critical to the process happening inside the lawn mower.

Here’s a thought to ponder: if you invest a good amount to buy your lawn mower, make the most out of it by providing it with the care and maintenance requirements that are essential to it. This way, you have a fully functional mower to help you maintain a well-manicured yard.

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