Why Is My John Deere Engine Surging? (Answered)

To say that the Deere brand is “iconic” would be the understatement of the year… and how. The company’s stellar reputation is built on delivering capable machines that seldom let you down. Deer mowers tend to adhere to this 184-year tradition of excellence, but they are not always infallible.

John Deere engine surging is a sign of some element of the fuel delivery system either being restricted or clogged. Areas to check for a solution to the problem include: gas caps, filters, fuel lines, and spark plugs. Either regular cleanout or replacement is advised.

Today’s article focuses on an all-too-common problem: engine surging. What is it? What causes it? More importantly…what are the possible solutions? 

Well, stick around and find out.


Signs And Causes Of A John Deere Mower Engine Surging

Picture this…

It’s a lovely Saturday morning and, as usual, you bring out your trusty Deere for your weekly lawn touch-up. Only this time, the mower’s motor RPM yo-yos up and down, regardless of how hard you push the accelerator. It revs at its maximum one moment, then seemingly runs out of steam the next.

The engine doesn’t completely peter out, but this occurrence is weird…and understandably concerning. After all, these machines cost a pretty penny.

In such a scenario, chances are your lawnmower (or, more specifically, its engine) is experiencing what is known as an engine surge.

This unpredictable RPM fluctuation is the classic sign of this problem. It is an issue that can occur during acceleration or when the machine is idling. Luckily for you, it is not all that rare.

John Deere engine surging is a result of an inconsistent combustion process in the engine cylinder(s). More specifically, it is caused by inconsistent delivery of fuel and/or oxygen to the combustion chamber. The usual problems lie in the air filter, gas cap, fuel lines, or carburetor.

As you know, for an engine to fire and produce power, it needs a combination of fuel, air, and a spark from a sparkplug to produce an explosion known as combustion

To facilitate this process, a lawnmower has a fuel delivery system (fuel tank, fuel lines, fuel filters, carburetor, etc.) and an air delivery system (vents, air filters, air inlet valves, etc.). These delivery systems and your sparkplugs must be in tip-top shape and free from blockages at all times.

Therefore, if your mower is surging, there are a few ports of call.

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Clogged Air Filters Can Cause Engine Surge

First, we recommend that you inspect the air filter. As the name suggests, this component is there to protect the engine from dust and debris that may be in the air. When working normally, the filter blocks these particulates and ensures clean air is delivered to the sensitive parts of the engine.

Over time, the build-up of dust and debris slows down the rate of this clean air delivery. Eventually, air (oxygen) won’t reach the combustion chamber at all or when it’s needed, resulting in inconsistent power output.

Slow Fuel Delivery Systems And John Deere Engines

The second thing you want to inspect is your fuel delivery system.

The Gas Cap

We recommend you start with simple things like your gas tank cap. These caps typically feature a small hole on the inner side. This hole is a clever piece of engineering that facilitates the creation of backpressure in the tank. This pressure helps push fuel into the fuel lines towards the carburetor.

Unfortunately, the small size of these holes makes them susceptible to blockages from dust or oils. Always check this first before completely disassembling your fuel system.

Fuel Lines

If the cap hole is not the issue, you should move on to the fuel filter and fuel lines. The filter is prone to debris blockages, especially if you use low-octane gasoline. Naturally, blockages result in inconsistent fuel delivery…which can cause surging.

Fuel lines are narrow tubes that deliver fuel directly to the carburetor. They are typically made of plastic and they are often transparent or semi-transparent, which makes it easy to spot blockages.


Next, we have the carburetor. This vital component has the delicate role of “spoon-feeding” fuel and oxygen directly into the combustion chamber. Delicate is an apt description for the carburetor, as even the smallest bits of gunk and debris can disrupt its functioning.

The carburetor is made up of a bowl, a float, and several valves. Dirt can negatively affect a bowl’s fuel carrying capacity and the movement of the float. Dirt can also block the inlet/outlet valves (commonly known as “needle valves” due to their small sizes). Regardless of the particular disruption, engine surging may be the result.

The carburetor is also prone to air and vacuum leaks when it is loosely attached to the engine block. This results in excess air flowing into the combustion chamber, which disrupts the delicate fuel/air mix necessary for efficient combustion. 

Even worse, a vacuum leak will negate the backpressure required to suck fuel towards the engine efficiently. Again, the fuel/air mix will be thrown out of whack.

Since many lawn mowers and tractors today are sporting Kawasaki engines, here is another article you may be interested in… Kawasaki Engine Problems: Diagnoses, Fixes, And Tips

How To Fix A Surging John Deere Lawn Tractor Engine?

Now that we’ve identified some of the problems behind a surging mower engine, let’s talk about some of the solutions you can opt for. There are two main actions you can take for any of the problems that could arise.

To fix a surging John Deere mower engine the problem must be diagnosed and then the component either cleaned out or replaced. With parts like filters and spark plugs, replacement is the best option. Oil should also be replaced on a regular basis. Carburetors can be cleaned or replaced.

Let’s take a look at some of these specifically…

Regular Service And Maintenance

The first (and highly recommended) thing to do is ensure the machine is serviced. This involves oil changes, sparkplug replacement, and air filter replacement. Foam air filters can also be cleaned using soap and water. Paper filters must be replaced.

Luckily, Deere mowers have specific service schedules that serve as a guideline for what needs to be done at specific milestones. These guides are provided by the manufacturer and are often attached to the back (or bottom) of the operator chair.

Oil Change

Oil changes are important for the smooth movement of the engine piston and other moving components. Deere usually recommends oil changes after about 50 hours of use.

Spark Plug Changing

This is usually an easy task for most John Deere machine owners. The difficulty for most will be knowing which spark plug to replace it with.

Spark plugs are not one size fits all or even one size fits most. Many brands formulate their own size and capacity of spark plug to fit their particular machines.

For more on how spark plugs work in mowers like John Deere and other major brands, I have an article that deals specifically with them. See Are All Lawn Mower Spark Plugs The Same?

Air Filter Replacement

Air filters are an important safeguard for keeping debris out of engine lines and cyclindars. These are most often an inexpensive way to cure some seemingly major problems.

Simply changing the air filter can dramatically improve the workings of a John Deere mower. These engines are built to run well and last. Yet, even these quality machines are reliant on clean air and fuel to operate.

Regular air filter replacement can stave off problems like engine surge.

To read more on mower air filters, see my article dedicated to just that… How Often Should You Change A Mower Air Filter?

Carburetor Issues

If you are certain that service isn’t the issue, you will have to look at the carburetor, which is often the prime suspect in this case. 

Most people are better off taking the mower to a repair shop. However, if you are confident, you can get in there yourself and have a look. 

If the carburetor is the problem, you must take it out, take it apart and clean it. 

We highly recommend a visit to Amazon for a carburetor cleaning kit with brushes and needles that you can use to push out gunk and debris. You should also dip the carburetor components in a carburetor cleaning agent to dissolve any particulates.

Finally, you must also inspect the bolts securing the carburetor to the engine block. Tighten any loose bolts you find to reduce air leaks and maintain vacuum pressure. Any worn-out gaskets between the carburetor, manifold, or engine must be replaced as these can facilitate leaks.

The Final Touches On Surging John Deere Engines…

Though John Deere is one of the leading names and manufacturers when it comes to quality lawn care products, even their engines as they rack up mowing hours can run into issues due to clogging or deferred maintenance.

Even with regular maintenance, sometimes parts will need to be either cleaned or replaced.

Engine surge itself is not the problem, but an annoying symptom of an underlying issue. Checking the parts surrounding the fuel delivery system is your best bet to diagnose and come up with a solution.




Mathew Booe

Mathew has worked in landscaping professionally for over 10 years. He is a grandpa and frequently interviews other experienced landscapers and lawn care experts who are also grandpas for these articles.

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