Lawn Mower Surging - Best Home Gear (2022)

Is your Lawn Mower Surging up and down every time you use it? If so, you’ve come to the right place! Today, we’ll share 6 simple steps that you can inspect and repair your lawn mower engine surging.

We probably agree that mowing your lawn is a real chore – and that’s when your gas-powered lawnmower is running well!

Unfortunately, small engines don’t always perform as well as we hope for; like when your lawn mower revs up and down.

This mower engine problem is due to one-of-three engine requirements not working properly:

Lawn Mower Engine – Performance Requirements”

  1. Fresh Gasoline (fuel)
  2. Fresh Air (oxygen)
  3. Good Spark (spark plug)

To make sure each of the above 3 requirements Is working properly – Look at the Six (6) potential problems below – that can cause Lawn Mower Engine Surges:

Six (6) Problems That Cause Lawn Mower Surging – And How To Repair:

1) Bad Fuel

The number one cause of mower engine surge is using gasoline that is old or contaminated – perhaps by water condensation, usually as a result of leaving gas in the mower over the winter.

(Video) How To FIX A SURGING ENGINE On A Lawn Mower, Pressure Washer, etc.

Many homeowners forget or choose not to drain the gas from their mower’s tank at the end of each season. At the start of a new season, they either add fresh gas to the old gas or try to start the mower engine using the old gas.

The quality of gasoline deteriorates quickly over time. For this reason, buy only enough gas you can use within 30 days. When your lawnmower sits idle over the winter with a half-empty gas tank – condensation builds up inside the gas tank and mixes that water (condensation) with the gas.

If the lawnmower does happen to start – it will not run properly with old or diluted gas in the tank. If your lawnmower surges up and down – you can repair it as follows:

How To Repair Bad Fuel in Lawnmower

  • Drain old gas from the tank. Use a siphon if you have one – and save spills on the engine and floor.
  • Add fuel stabilizer to the gas tank (manufacturers recommended mix ratio) and top with a full tank of gas.
  • Run the engine for 2 minutes to circulate the fresh gas. Check for mower engine surging.

Tip: Briggs & Stratton recommends only using gas for small engines with no more than 10% Ethanol, and that has a minimum 87 Octane rating. This is one way to keep your Briggs & Stratton engine surging issue, from happening.

Briggs & Stratton Video Best Fuel For Lawn Mower Engine:

Alternative Fuel: “Pre-Mixed” Lawnmower Gas:

You can also choose to use “Canned (or Boutique) Fuel” for 2-Cycle small engines, discussed here at Popular Mechanics.

It may sound weird – but canned fuel for mowers does provide 3 important benefits to your lawnmower engine vs. typical gas pump fuel.

(Video) How To Fix A Surging Engine on a Lawn Mower, Generator, Pressure Washer & More

  • Canned fuel contains Gas – but No Ethanol (Ethanol is a grain-based by-product) is used to make petroleum fuels more affordable, and actually does more damage than good to engines.
  • Canned fuel has a High 94 Octane rating – Provides superior engine performance
  • Canned fuel includes Stabilizer to protect engines

We recommend VP Small Engine Fuels at Amazon – as the best choice of canned fuel available online.

2) Dirty Lawn Mower Air Filter

Lawn Mower Surging - Best Home Gear (1)

If you find that your Briggs & Stratton mower engine revs up and down (surges), it may be likely that your lawnmower air filter is dirty.

As noted previously, mower engines require air (oxygen) mixed with fuel, then spark, to ignite the mixture and run the lawnmower engine.

If your air filter is dirty – it’s like forcing your lawnmower engine to “suck air through a straw” – and nothing runs efficiently under those conditions.

How To Repair Dirty Lawnmower Air Filter

  • Remove the lawnmower air filter
  • If your lawnmower has a “Foam” type reusable air filter, follow instructions to wash, dry, and reuse the lawnmower filter.
  • If your lawnmower has a “Paper” type (disposable) air filter – simply replace the air filter with a new one to match your lawnmower air filter requirements.

If You Need To Replace a lawn mower air filter – You can use the links below for the most popular brands. Be sure to verify specifications that the air filter you select matches your existing filter:

3) “Clogged” Lawnmower Gas Cap

Lawn Mower Surging - Best Home Gear (2)

Most people are unaware that the fuel tank “cap” has a small hole on the top, which allows air to enter the gas tank and create back pressure. This air pressure helps deliver fuel to the carburetor and run correctly.

Sometimes, when a lawnmower surges up and down it’s because the gas cap hole is clogged with dirt or debris. Not to sound too redundant; lawnmower engines need a steady flow of fuel delivered from the gas tank to the carburetor to perform as designed. Use 2 steps below to make sure the gas cap is not clogged:

(Video) Riding Mower Engine Surging - Easy & Inexpensive Fix!

How To Repair Clogged Lawnmower Gas Cap

  • Inspect the Fuel Cap for a clogged hole.
  • Use a small piece of wire or compressed air to clean any obstruction in the hole.

4) Vacuum Line Leak

Lawn Mower Surging - Best Home Gear (3)

The lawnmower carburetor is designed to operate with a controlled amount of air intake. If you have leaks in your air intake – the carburetor and therefore the engine – will not run smoothly. Try these 5 steps which require minimum tools, to inspect your lawnmower for vacuum leaks:

How To Repair Lawnmower Vacuum Leak

  • Inspect vacuum hoses leading from the air filter to the carburetor.
  • Check vacuum hoses for cracks, holes, or loose hose clamps, and fix or replace as needed.
  • Check the condition of the Carburetor Gasket – Replace if needed.
  • Tighten carburetor (4 bolts)
  • Tighten engine manifold bolts to ensure a tight vacuum seal.

5) “Bad” Lawnmower Spark Plug

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Without a proper spark delivered from the lawnmower engine spark plug, the engine will not run correctly. If you’re not sure How to tell if a lawn mower spark plug is bad, check out this article from Best Home Gear.

We recommend the following 4 steps to inspect and repair a bad spark plug:

How To Repair a Bad Lawnmower Spark Plug

  • Disconnect the spark plug wire
  • Carefully remove the spark plug
  • Inspect the spark plug for any cracks or a worn-out electrode.
  • We recommend you replace the spark plug with a new spark plug – use the same size recommended by the manufacturer.

6) Dirty Carburetor

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The role of the carburetor is to mix the perfect ratio of gas and air. It does so, with tiny jets and passages designed to get the correct air/gas ratio to the spark plug. Sometimes the jets can get clogged with dirt or debris or corrosion which can also be caused by using old gas.

Therefore, fixing a surging lawnmower engine can be just a matter of cleaning the carburetor.

In short: The main carburetor jet supplies gas to the engine during the engine’s full throttle. When that main jet gets blocked the engine stalls, as no fuel is being delivered.

As soon as the engine stalls, a governor on the engine automatically closes the engine’s throttle. This situation causes the carburetor idle circuit to supply fuel and the engine – which will fire again, returning the throttle to full.

(Video) Briggs and Stratton, Lawn Mower Engine Surges, Troubleshooting Surging, Low Idle RPM No Power Fixed!

If the carburetor is not cleaned, this stall and firing cycle will repeat itself, again and again, causing the engine to die and then surge. You can try these 5 steps to clean a dirty lawn mower carburetor:

How To Repair Dirty Lawnmower Carburetor

  • If you’re handy with tools, remove the carburetor and clean it with carb cleaner
  • Inspect and replace any torn gaskets
  • Securely tighten the carburetor after cleaning.
  • Alternate method: If you’re not comfortable removing and repairing the carburetor – try using a carburetor cleaner spray. For under $4.00, you can spray the carb cleaner directly into the carburetor without removing it.
  • If this method doesn’t effectively clean the carburetor – you may require the service of a small engine repair technician.

Frequently Asked Questions (FAQ) Lawn Mower Surging

Why Does a Lawnmower Engine Backfire?

Even though it sounds bad – an engine backfire does not typically damage a small engine. It can, however, be a sign that one of the following issues is occurring:

  • Using gasoline with too much alcohol – (Use maximum recommended 10% Ethanol)
  • Turning the engine speed down too quickly (lower engine throttle slower)
  • High engine temperatures (mow during cooler temperatures – or mow in two shifts – if possible)
  • Lack of adequate air (dirty filter)
  • The carburetor is running lean (adjust carburetor for proper air/gas mix)

How Do You Know If Your Spark Plug is Bad?

A bad spark plug will certainly cause your lawnmower to run poorly or not at all. Fortunately, it is fairly simple to determine if your Spark plug is bad, and needs to be replaced. If you’re not sure what to look for, check out this quick article How To Read a Spark Plug

How Should You Store Lawn Mower for Winter?

Before lawnmower storage – you should always add a good fuel stabilizer to the tank (such as Sta-Bil) – then fill the tank completely with fresh gas. Next, run the mower engine for 2 minutes to circulate mixed gas through the engine. The fuel stabilizer will keep gas stable for up to 24 months.

What Is The Best Way to Fix Bare Patches on Lawn?

Bare patches in your grass lawn can be the result of many causes. The most prevalent are pet urine and bug infestation, both of which can be fixed in a jiffy. Check out our article and learn how to plant grass seeds in bare spots.

How Do You Change Oil On Lawn Mower?

Changing the oil on a lawnmower is actually quite easy. Make sure the engine and engine oil are cool – and before you start, read this quick 4-step oil-changing guide from Briggs & Stratton.

Conclusion:

While lawnmower engines require some routine maintenance, they are usually a very dependable piece of outdoor equipment – considering the work and conditions that they perform.

(Video) How to Fix a Surging Lawn Mower

As with owning any equipment with a small engine, lawnmowers also have 3 basic requirements to ensure dependable performance. Clean gas, Good Air Flow, and Proper Spark.

We hope this Mower Guide for solving lawn mower surging has been beneficial – and that one of our five solutions did the trick!

Thanks for Visiting Besthomegear.com – Please don’t hesitate to leave us a Comment or Suggestion Below!

References and Additional Reading:

  • How To Dispose of Old Gasoline – WikiHow.com
  • How To Sharpen Lawn Mower Blades – Besthomegear.com
  • The Best Way To Store Gasoline At Home – Familyhandyman.com
  • The Best Self-Propelled Lawn Mowers – Besthomegear.com
  • The Best Gas Fire Pit Tables for 2020 – Besthomegear.com

FAQs

How do you fix a surging lawn mower? ›

And you want to run one of the tip cleaners. Inside the jet. So you'll have to figure out which one

What causes a lawn mower to surge? ›

Why is My Lawn Mower Surging? (The Short Answer) Surging results from the engine having an unbalanced fuel-to-air mixture ratio. The most likely fault you'll run into will be a problem with the carburetor resulting in the fuel-air mixture erratically running lean or rich.

Why is my lawn mower surging up and down? ›

Airflow Issues. A lawnmower that hunts and surges may be experiencing something as simple as an airflow issue. If the air that the engine requires to run is blocked, especially sporadically, it can cause the engine to slow down. When the blockage moves or clears, the engine may suddenly rev up in response.

How do I fix my Briggs and Stratton engine surging? ›

Back into the carburetor right there turn it all the way in and then turn it out one and a half

What causes a small engine to surge up and down? ›

Carburetor Issues

A dirty or gummed up carburetor causes an engine to surge. If you feel comfortable working on carburetors, unbolt the bowl and clean it thoroughly. Check whether the float moves up and down without sticking, and clean the tiny ports on the bowl hold-down bolt.

What causes an engine to hunt and surge? ›

Engine hunting and surging at idle is usually caused by a fuel delivery, air leak, or governor system problem. Cleaning/overhauling the carburettor, adjustment of the governor, and/or changing the air filer may be required.

Can spark plugs cause surging? ›

Surging and Lagging

Another good indication that your spark plugs are dirty or worn is if your vehicle experiences surges of speed, resulting in a jerking acceleration. These surges occur because your spark plugs are not igniting the fuel in your engine at the proper rate, resulting in an uneven speed.

How do you fix a surging governor? ›

Often surging caused by the governor can be fixed by simply adjusting the governor spring. It usually only takes a small adjustment to correct the surging. If the spring has stretched out it will need to be replaced.

Why is my lawn mower not running smoothly? ›

A dirty air filter is one of the most common causes of a poorly running lawn mower, since it starves the engine of the oxygen needed for combustion. Fuel Filter: Check the fuel filter on the mower to make sure it's clean, and replace it if needed.

How do you fix a surging governor? ›

Often surging caused by the governor can be fixed by simply adjusting the governor spring. It usually only takes a small adjustment to correct the surging. If the spring has stretched out it will need to be replaced.

Why is my lawn mower not running smoothly? ›

A dirty air filter is one of the most common causes of a poorly running lawn mower, since it starves the engine of the oxygen needed for combustion. Fuel Filter: Check the fuel filter on the mower to make sure it's clean, and replace it if needed.

What does engine surging mean? ›

Engine surging is usually a warning sign that your car or truck is having combustion problems. Since a vehicle's ignition wires and spark plugs play a major role in proper engine performance, it is likely time to check your engine's electrical components.

Why is my lawnmower hunting? ›

The most common cause for engine hunting is a blockage in the carburettor. Put simply, this restricts the fuel flow in the carburettor causing the engine to slow down. To try to compensate for this, the engine's governor opens the throttle to allow more fuel into the engine.

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