Lawn Mower Won’t Start When Hot | Causes & DIY Fixes

It doesn’t matter what kind of lawnmower you own. You might have the most expensive market model, such as Honda, Briggs and Stratton, or having one a few years old. There a million other things to do besides mowing but doing those things won’t give you a great lawn.

If your lawnmower doesn’t start after it’s been running for a while, the problem may be easier to fix than you think. Although a warm mower usually means that you’ll complete the job, several environmental and mechanical conditions might make your lawn mower shut down. Some remedies have already been included in most manuals, but others require a closer look, and as always, the proper safety precautions before troubleshooting the problem. 

Therefore, let’s dig into some of the common reasons why your lawnmower won’t start once it’s warmed up and look at the possible solutions you can implement to fix it. This article will guide you through the reasons while providing you with the solutions. Note that the solutions are arranged as per the severity of the problem and should be implemented accordingly. 

Major Causes Of “Lawn Mower Won’t Start When Hot.”

Irrespective of the make and model, hot engine problems can fall on any gardener at any time. You prime up your engine most of the time, but it fails to start despite being warmed up. You do the essential inspections and accordingly check the oil level, change oil in your mower, spark plugs, air filter, and so on, but the mower still refuses to start. Starting a gasoline lawnmower is frustrating enough already. However, your patience is tested even more when the mower stops all of a sudden and refuses to restart.

Here are a few of the major causes why your lawnmower won’t start when hot

1. Engine Overheating
2. Faulty Spark Plug
3. Faulty Choke

1. Engine Overheating

This can cause severe damage, common reasons for an overheating mower: engine running lean; using a wrong plug or fuel type; air cooling fins obstructed. This is one of the primary reasons why your mower won’t start. There are several reasons why your engine overheats. At times, dry leaves can get accumulated inside the muffler, causing the engine to overheat.

The more these dry leaves accumulate inside the mower deck; they slide directly into the muffler. Similarly, if the grass is left to grow out too far, it can create clippings. As a result, particles can flow up in the mower deck and contact the muffler, clogging the engine and causing it to overheat.

The average lawnmower is not built for handling field grass. However, if you mow a field using a standard lawnmower, the dry leaves can get in the muffler and overheat your engine. Your mower engine generates a lot of heat, and therefore the heat dissipation must be equivalent to the heat generated.

If the heat dissipation isn’t enough, then it puts your mower at risk of bursting into flames. Similarly, the cooling fins attached to the mold can overheat due to holding too much heat closer to the engine. This ultimately leads to smoke coming out of the lawnmower and can result in your mower catching fire.

2. Faulty Spark Plug

Every spark plug has a small gap between two electrodes. Every time the spark jumps across this gap, it causes combustion the minute air mixes with gasoline. However, if the gap isn’t of the adequate length, then that widens the heat gap, ultimately shutting the mower down. As a result, always check the manual to see whether the two electrodes’ gap is adequate.

A frayed wire leads to an abnormal connection to be formed at the two nodes of an electric circuit, which generally results in circuit damage, explosion, or ignite a fire. When using an electric lawnmower, there are higher chances of choking inside the carburetor getting severely damaged. To manually check this, you must know where to locate the carburetor on your lawn mower though. Few of the latest lawnmower engines come equipped with a thermostatically controlled automatic choke system with a simple set-up.

The spark plug is the most likely cause of a hot starting problem and is the most straightforward problem to solve. The mower won’t start without a spark on the plug. Using a simple test mentioned below, you can quickly check your ignition system and detect whether the coil is faulty or note

3. Coil And Plug Test

For this test, the tools you need are: 

• A new spark plug
• Plug spanner
• Insulated pliers

Once you’ve gathered all the materials, follow the steps mentioned to perform a simple coil and plug test.

Hold the spark plug against the metal engine with the help of insulated pliers. Note that the spark plug must always be fully grounded when in contact with the engine.

Step 1: Replace the plug with a test plug

Step 2: Check for spark

Step 3: Get somebody to start the mower while you observe the spark.

Step 4: If there is less or NO spark, then it indicates that you have a faulty spark plug. 

Step 5: However, if you get a decent enough spark but the problem continues to persist, then your carburetor requires a thorough cleanse

Step 6: When done with the spark plug, check the plug wire for damage or chaffing.

Step 7: If the wire is intact, move on to check the bail and switch.

Step 8: Check to see if the bail lever is tight. If not, adjust it accordingly. For the mower to start, the bail lever has to pull all the way.

Step 9: The bail lever is connected to the engine that has a simple off switch. Upon releasing the lever, the engine slows down, precisely when the on-off coil switch comes into play. 

Step 10: Once everything is checked out, remove the assembly and replace the coil. 

Step 11: Remove the two bolts holding the wire connector and then remove the push on the wire connector.

Using this simple test will quickly help you determine whether you have a faulty spark plug or note. Remember that the spark plugs come in a variety of lengths and heat ranges. Fitting the wrong plug into your mower can often be the reason why your mower isn’t starting when hot. Therefore, it is always a good idea to check whether the spark plug is compatible with your mower or not. 

Always have a spare spark plug handy as it allows you for easy and quick troubleshooting by simply replacing the existing spark plug with the spare one. A spark plug fouled with carbon from long hours of mowing also can fail to spark. Replace a spark plug that is damaged. 

4. Faulty Choke

When using an electric lawnmower, there are higher chances of choking inside the carburetor getting severely damaged. However, if the lawnmower is used in such a condition, the choke remains closed even when the engine starts. It floods the engine. A flooded engine ultimately means less heat dissipation and more overheating, resulting in a fire outbreak. Similarly, if the mower solenoid goes wrong, it can lead to engine overheating as well.

The choke is designed in such a way that it opens up every time the engine starts. However, in case of a malfunction, the choke fails to open and sticks to the engine causing the machine to be flooded. This happens because the closed choke doesn’t allow enough air to enter the engine. The easiest solution to this is removing the air filter and duly cleaning the air filter.

However, these problems mainly arise with those automatic chokes which are prone to overheating. In such cases, go ahead and replace the carburetor if you have an automatic choke. A choke can malfunction if the carburetor supplies too much fuel to the cylinder or the gasket. If you try to restart your engine when hot, the engine gets flooded, and the spark plug keeps your engine from starting. 

Here are some valuable tips that can help you determine whether your choke is functional or defunct

• If your lawnmower engine has a primary bulb-type choke and smokes when you try to restart it, it means that your carburetor needs to clean or replace
• If you have an auto choke, there won’t be a choke lever. In this case, you will have to auto choke. Check your choke plate when the engine is hot. An open choke plate means your choke is good to go. However, a closed choke plate means that your carburetor needs to be cleaned or replaced.
• The choke should permanently be CLOSED when starting a cool engine.
• Always see to it that the choke plate is closed when you start a cold engine. 
• If not, check for binding or fault with the thermostat choke control unit – fitted against the muffler.

Minor Causes “Lawn Mower Won’t Restart When Hot.”

1. Air Leaks

An air leak causes an engine to absorb too much of the outside air. This results in the engine not dissipating the heat generated by the mower and eventually shutting down. Unless the engine can dissipate the heat, it won’t start.

You will be able to start the engine once it cools down, but this problem will keep occurring over and over. A simple solution is to remove the plastic shroud at the top of the mower and to shut down the engine. Once the cover is off, you can clean the engine with compressed air, clean out the fins and the shroud’s underside. 

2. Low Oil Level

In any combustion engine, oil is used both as a coolant as well as a lubricate. However, whenever the oil level dips, it causes the engine temperature to rise. Similarly, it causes the heat dissipation to decrease, which is why the engine overheats, and your mower won’t restart when hot. The oil keeps the engine components such as coils and plugs well lubricated because they can function efficiently. However, if the adequate amount of oil does not reach these coils and spark plugs, they cease to function, causing the engine to overheat. 

3. Problematic Compression

Whenever the mower doesn’t start or restart, it is generally because of a mechanical problem. A problematic compression could be one of the reasons why your mower won’t start. Detecting a faulty or poor compression is easy. Whenever your mower’s starter rope begins to move around more quickly than it did before, then it means that your mower may be suffering from poor compression.

An overheated engine could worsen this situation. The only smart thing to do here is to contact a small-engine repair person at the earliest. NEVER try to do repairs whenever there is an internal engine problem.

While it sure is fixable and if your lawn mower is still giving you headaches despite trying all these fixes, getting professional help might be your last resort. In case you decide to scrap it, my guides would help you research for better models –

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The Bottom Line

We hope our article could walk you through every possible reason why your lawnmower won’t restart when hot, along with the possible solutions you can apply to get it started. Remember that these are some of the most common causes why your mower isn’t starting. Always read the safety manual before you get to fixing your mower.

Do NOT forget to wear the right safety outfit when working with a lawnmower. If there are issues with your internal engine, contact a qualified maintenance specialist immediately and do not try to solve the problem yourself. 

There may be issues with the cylinders and intake gasket that can cause a faulty compression. Replacing a cylinder or intake gasket is not at all expensive. However, if the problem lies deeper into the engine, it is not economically feasible to repair. To ensure whether your mower has a mechanical fault, you can take the compression test by using a compression test gauge. You can buy a compression test gauge from the following link:

Remember that your engine won’t restart most of the time when hot because your mower may be old. If you have a mower you’ve been using for over ten years and face this problem, it is best to get a new mower without any second thoughts.