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What Causes A Lawnmower Engine To Surge?

The lawn mower engine is an internal combustion engine that is used in lawn mowers. The purpose of the engine is to power the mower blades with a spinning motion. 

The lawn mower engine is an internal combustion engine that runs on gasoline or petrol. It is used to power lawnmowers and other similar machines. 

A common type of lawnmower engines is the 4-stroke engine. The 4-stroke engines are much common than the 2-stroke engines because they produce more torque and cleaner combustion for better performance.

Engine surging is a common problem that lawn mower machines have been experiencing over the years. The most common reasons for engine surges are bad spark plugs, faulty carburetor, dirty air filter, gasket vacuum leak and governor control fault. 

Engine surges can be easily rectified by following the steps mentioned below. Today we’ll be discussing some of these causes in detail.

A lawn mower that is surging
A surging lawn mower

Some of the vital causes for a lawn mower engine to surge

  1. Bad gas
  2. Bad spark plug
  3. Dirty / faulty carburetor
  4. Dirty Air Filter
  5. Gasket vacuum leak
  6. Governor control fault

Bad gas in the tank

A lawnmower engine could surge due to bad gas, because the gas is too old or because the tank is not filled up. Gasoline can be left in the tank for about a week, but it should never be drained completely. 

A half-empty gas tank is not a problem and should not cause the lawnmower engine to surge. If your gas tank is not very full when you store it for winter, there is a risk that the gas will absorb water and become diluted. 

This might cause it to leave water droplets in the tank or cause an engine surge when you start it up at the beginning of spring. The best way to avoid this is to always keep your gas tank almost full during winter storage. 

Bad spark plug fails to burn fuel efficiently

A lawnmower engine is designed with a spark plug to provide the right amount of energy for an engine to start and run smoothly. A lawnmower engine will not function properly without a spark plug. 

The spark plug ignites the fuel and air mixture in the cylinder chamber. A bad spark plug is the cause of a lawnmower engine surging. 

This will lead to high fuel consumption as the engine will not be able to accelerate properly because it’s not getting enough power from the spark plugs. 

A bad spark plug can be caused by an improper electrode gap or worn-out electrodes that no longer conduct electricity properly. Without a proper spark plug, the lawnmower engine will misfire as it tries to turn on. 

The fuel will not be burned as efficiently as it should be, and all this can lead to a surge in engine performance. If your lawnmower engine is surging or misfiring, you might want to check the state of your spark plugs first before replacing them with new ones. 

A lot of people are reluctant to work on their own mower because they think that they might break something or make it worse. However, replacing spark plugs is an easy process that doesn’t require any special training or skillset. 

Even if you break something, the worst-case scenario would be to replace the part with a new one for a few bucks.

Faulty lawn mower carburetor can’t mix the fuel correctly

A carburetor is a device that mixes the perfect ratio of gas and air for an internal combustion engine. The purpose of the carburetor is to mix the perfect ratio of gas and air. It is designed to get the correct air/gas ratio.

If the carburetor is out of adjustment, the engine will not be able to use all its fuel mixture for combustion. If the carburetor is set up wrong, there won’t be enough fuel getting to the engine. 

Faulty lawn mower carburetor
Faulty lawn mower carburetor

This will cause the engine to surge because it has too much fuel in it. A dirty or faulty carburetor can’t mix the fuel mixture correctly. If the bowl vent valve is stuck open, it will allow fuel to flow freely through the carburetor. 

This will cause the engine to surge. If this happens, you must replace the bowl vent valve. A bad fuel filter can’t keep debris out of your engine and carburetor, which can lead to surging or lack of power.

You’ll also notice your lawn mower is running slow due to a faulty carburetor. To fix this problem, you should inspect the carburetor for any torn gaskets or dirt. You should also remove and repair any damage that was done to it if there is anything. 

Finally, you should securely tighten the carburetor after cleaning it off to avoid further issues with your car engine in the future. This process might require more expertise than replacing the gasket or tightening bolts, so be sure to consult an expert before starting this step.

Dirty air filter causes engine to run with lower output

If you have a dirty air filter, it can cause your mower to surge on startup. This is because the engine is receiving less air than it needs and starts sputtering and misfiring. 

The engine will also run with lower power output and the gas mileage will likely be reduced. When you’re cutting thick weeds or high grass, the engine may sound like it’s struggling with these tasks. 

Dirty air filter on a lawn mower
Dirty air filter on a lawn mower

The exhaust system may give off a strong gasoline smell that fills the air when you’re mowing in hot weather. A dirty air filter will make the lawn mower inefficient. 

When the air filter is dirty, it can cause internal damage to the engine. You should fix the air filter to overcome the issue.  Removing the air filter from a lawn mower is one of the easiest tasks to do. 

Start by removing the spark plug wire from the spark plug. This will prevent you from accidentally starting your lawn mower and getting injured. 

Pull out your lawn mower’s air filter and wash it with soap and water, then dry it before putting it back in. If you would like to reuse your old filter, rub some mineral spirits on it before putting it back in.

If you find that your old filter is too worn out or damaged, replace your old filter with a new one so that you can always have a clean machine for any job!

Carburetor vacuum leak symptoms

The lawnmower carburetor is designed to work with a controlled amount of air intake. A gasket vacuum leak causes the engine to surge because when not enough air enters the combustion chamber.

This throws the gasoline mixture out of balance. This unbalances the gas-to-air ratio and releases unburned hydrocarbons. This can cause irregular engine performance. 

The unbalance in the gas to air ratio will make it difficult for the engine to run smoothly.

Fixing a vacuum leak in a lawn mower engine is the best way to prevent surges. Properly routing hoses can help prevent surge due to vacuum leaks. 

When you are repairing vacuum connections always make sure that they are tight and secure. Find the location of your vacuum leak. 

When you have found it, take off the hose and inspect it for signs of wear or damage. If there is no visible damage, try fixing the connection by either tightening it or replacing the hose entirely.

Faulty governor controller

Governor control fault is one of the most common causes for this problem. The governor is a system that regulates the mean speed and controls the fuel to the engine cylinders. 

When an idle speed control motor becomes fouled by carbon buildup from gasoline residue, it will cause surges in engine power and leads to high fuel consumption. 

This will make it difficult for the governor to maintain a constant mean operating speed and may lead to shutdowns or malfunctions in other parts of the fuel system. 

The best way to fix this problem is to clean the component and repair or replace it if needed.


For any engine to run smoothly, it needs to be properly maintained. If you neglect these routine maintenance tasks, your lawn mower engine could experience problems like surging or backfiring as the Kholar engine do.

Some of the vital way to avoid these problems is by performing the necessary fixes and following certain guidelines like ensuring clean gas, good air flow and proper spark. 

We’ve discussed some of the major problems associated with surging lawn mower engines. If you still have problems performing these fixes, contact a professional repair service.

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