Kohler Engine Runs Rough When Hot-Causes and Fixes

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If your Kohler engine runs rough when it gets hot or sputters when engaged at full throttle, it can be quite annoying as it will definitely slow you down, especially if you have a lot of mowing to do.

In this article, I share the common reasons your Kohler engine suddenly runs rough when hot and practical steps you can follow to diagnose and fix these problems.

Reasons Why Your Kohler Engine Runs Rough When Hot

Your Kohler engine may run rough when it gets hot for the following reasons:

  • Old fuel/water in the fuel tank
  • Clogged fuel filter
  • Choke set in the wrong position
  • Dirty carburetor
  • Bad/dirty spark plug
  • Ground speed is too fast

Tools You Need For The Job

Some helpful tools you need to have close by before troubleshooting and disassembling your lawn mower’s engine include:

  1. Work gloves
  2. Screwdriver
  3. A clean rag
  4. Wire brush
  5. Socket wrench
  6. Pliers
  7. Empty fuel can

Kohler Engine Runs Rough When Hot: Possible Causes and Fixes

1. Old Gas Or Water In The Gas Tank

The first thing you want to check if your Kohler engine is running rough is the fuel tank to see if water hasn’t mixed with the oil. It might also be that the gas in your tank is too old.

The oil in your lawn mower might start to break down and lose its main qualities as soon as 30 days after purchase. Most fuels contain ethanol, an environmentally friendly substance that is added to fuel to make it more efficient by enhancing its octane rating.

Ethanol normally attracts moisture from the air. As the gas components break down with time, it leaves behind a sticky residue which can cause problems in the fuel system over time. Your lawn mower may run rough due to fuel restrictions caused by this.

Additionally, the presence of water in the fuel system can make the engine run rough when hot. This may occur if the lawnmower is left outside in a heavy downpour.


  • Drain out the old fuel into a container or fuel can using a siphon
  • Fill the fuel tank with new fuel if water or impurities are found in the fuel

2. Clogged Fuel Filter


Another thing you want to check is the fuel filter. The fuel filter prevents dirt and other contaminants from getting into the fuel system. It strains the fuel as it exits the tank. 

When the fuel filter is clogged or the fuel is too unclean, the filter may block or limit the flow of fuel. This limited fuel supply can dehydrate the engine, causing your Kohler engine to run roughly when it is hot.


Replace the clogged fuel filter with a new one.

3. Choke set in the wrong position

A wrongly positioned choke can also be the culprit. Check to see that the choke of your lawn mower might be set in the right position if it runs rough when hot.

The choke limits airflow to allow more fuel into the combustion chamber when the engine is being started up. Once the engine has warmed up, the choke needs to be changed(opened) so that fuel and air can mix and drive the engine.

Your Kohler engine will run rough or cease to work properly if the choke is not set properly once it has warmed up. This is because it is not receiving enough airflow.


Open the choke completely after the lawn mower engine starts running to allow airflow into the engine.

4. Dirty Carburetor


The next thing you want to check if your Kohler engine still runs rough when hot after examining the choke is the condition of your carburetor. 

The fuel pathways in the carburetor might clog up with deposits from old fuel and engine dirt, which can cause the small engine parts to stick and stop functioning as intended. 

This could make the engine run rough by preventing the proper amount of fuel and air from reaching the engine.


Clean the carburetor. You can do this yourself if you have technical skills or visit a small engine repair shop to get it done.

5. Bad/Dirty Spark Plug


A spark plug that is unclean and covered in carbon buildup or oil may also cause your Kohler engine to start running rough and experience sporadic operating issues.

When the electrode is burned, the plug is fractured, or the tip is particularly dark in color, your spark plug needs to be replaced. 

Ensure the spark plug gap is accurate and the spark plug wire is firmly fastened to prevent your lawn mower from running rough when it gets hot.


Remove the spark plug and swap it out for a new one with the aid of a socket wrench.

6.  Ground Speed Is Too Fast

Not adjusting the speed of your lawn mower according to your mowing conditions could be the reason your Kohler engine runs rough when hot.

You should adjust your mowing speed depending on the condition of the land you are working on to avoid overworking your Kohler engine.

Cutting dense or tall grass requires a slower ground speed than cutting thin and sparsely covered lawns, to prevent overtaxing the engine.


Reduce the mowing speed of the lawn mower when cutting tall and thick grass.

Kohler Engine Sputters At Full Throttle: Causes And Fixes

If your Kohler engine sputters at full throttle, it might be because of one or more of the following:

  • Old fuel residue
  • Clogged/dirty air filters
  • Damaged fuel cap vent
  • Dirty carburetor
  • Water in the fuel tank or fuel line

1. Old Fuel Residues

Fuel that has spent over 30 days in your lawn mower can be dangerous to the engine. It evaporates over time leaving behind sticky impurities that can affect the engine performance.

These impurities can clog different parts of the engine and cause your Kohler engine to sputter when set at full throttle.


Pour out the content of the fuel tank and replace it with new fuel.

2. Clogged/Dirty Air Filters

One of the most prevalent causes of lawn mower sputtering is dirty air filters.

The fuel supply to the combustion chamber of your Kohler engine may get obstructed by dirt in the openings leading from the carburetor and fuel filter.

The engine gets dehydrated at full throttle due to insufficient fuel getting into the engine as a result of this.


  • The clogged air filter should be replaced with a new one
  • Change your air filter at least once every year to prevent reoccurrence 

3. Damaged Fuel Cap Vent

The fuel cap vent allows air into the fuel system for proper combustion of fuel in the engine.

Too much or too little air can be allowed to enter your fuel tank if the fuel cap vent is not working properly. This results in a vapor lock which can cause your Kohler engine to sputter at full throttle.


Replace the fuel cap if it is bent or obstructed.

4. Dirty Engine Carburetor 

Deposits from old fuel, by-products of hydrocarbons, and fuel combustion can block different functional parts of the carburetor. These obstructions can cause your Kohler engine to sputter at full throttle.


  • Clean the carburetor using a carburetor cleaner spray
  • Replace the carburetor or take it to a small engine repair shop if the damage is severe

5. Water In The Fuel Tank Or Fuel Line

Your Kohler engine cannot fully ignite correctly when there is water present in the fuel tank. Water in the engine leads to compression issues which affect the performance of your Kohler engine. 

Take off the cover and search for water in the gas tank. If there is a separation of liquids (water and fuel), it is most likely the reason your lawn mower sputters at full throttle.


Drain out the old fuel and replace it with a new one. 


The reason your lawn mower runs rough when hot could be a clogged air filter, dirty carburetor, old fuel residues, dirty/faulty spark plug, etc.

Follow the recommended fixes in this article to solve these issues. If the problem persists, take it to a nearby small engine repairer who can examine the engine.