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Fix Lawnmower RPM: Troubleshooting and Repair Tips (2023)

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how to fix lawnmower rpmFeeling like your lawnmower RPMs are stuck in overdrive? Like a runaway train, it seems there’s no way to slow them down, let alone bring them back under control. Don’t worry; fixing the surging RPMs of your lawnmower is easier than it looks! With just a few simple troubleshooting and repair tips, you can be back to mowing smoothly in no time.

Key Takeaways

  • Dirty spark plugs, contaminated fuel, and clogged fuel lines can cause surging RPMs in lawnmowers.
  • Regular maintenance, such as cleaning the air filter and inspecting the governor, can prevent surging RPMs.
  • Proper cleaning techniques, like ultrasonic cleaning for the carburetor, can effectively address surging RPM issues.
  • Restoring reliable operation requires following the outlined steps and achieving stable RPM regulation.

Common Causes of Surging RPMs in Lawn Mowers

Common Causes of Surging RPMs in Lawn Mowers
Let’s explore some common causes of surging RPMs in lawn mowers. A dirty or incorrectly gapped spark plug, along with contaminated fuel or clogged fuel lines, could be the culprits. It is also worth checking the air filter for any clogs, inspecting the governor spring, and considering when you last performed basic maintenance tasks like changing the oil.

Spark Plug and Fuel Issues

You’ll want to check your spark plug for dirt and proper gap, make sure you have clean, fresh fuel in the tank, and consider using some carb cleaner and giving that carburetor a good cleaning. Troubleshooting carburetor cleaning, fuel line inspection, spark plug maintenance, carburetor jet check, and carburetor disassembly can help diagnose spark plug and fuel issues causing surging RPMs in your lawnmower.

Inspecting the air filter and spark plug, checking for obstructions in the carburetor jets, and ensuring fresh, clean fuel will help smooth out RPMs.

Air Intake and Governor Problems

You could examine the governor spring for obstructions that might be throwing off the engine’s RPM regulation. The pneumatic governor uses an air vane to maintain RPMs. Check for issues with the governor spring tension or position that could lead to surging.

You may need to remove the starter to access the air vane mechanism. Adjusting the governor spring tension properly and troubleshooting the air vane governor can help smooth out engine surging. Throttle plate obstructions and air filter saturation issues can also cause combustion ratio problems and RPM fluctuations.

Basic Maintenance Neglect

Try starting the mower without the air filter to see if that smooths out the surging RPMs.

  • Neglected oil changes increase friction.
  • Fouled spark plugs misfire erratically.
  • Clogged air filters restrict airflow unevenly.

Stay ahead of deterioration. Perform regular maintenance such as timely oil changes, replacing fouled plugs, and cleaning filters.

Diagnosing and Resolving Gas-Saturated Air Filter

Diagnosing and Resolving Gas-Saturated Air Filter
Having issues with your lawn mower engine surging up and down unpredictably? A gas-saturated air filter is often the culprit, causing your mower to run poorly and surge erratically. To diagnose and resolve this, inspect the air filter to see if gasoline has spilled on it, depriving the engine of oxygen.

Then, remove and replace the soaked filter, available at your local home store, to restore proper airflow and smooth operation.

Symptoms of a Saturated Air Filter

That despairingly fuel-crazed air filter is robbing your poor engine of precious oxygen! Fuel contamination starves your engine, causing surging RPMs and sputtering performance. Try preventive measures like inspecting the air filter routinely and using fuel stabilizers.

If troubleshooting points to a saturated air filter, get replacement filters and clean the carburetor. Soaking the main jet in carb cleaner can restore smooth airflow. With some elbow grease optimizing your air intake system, that oxygen-deprived mower will be revived and roaring with power again in no time.

Steps to Remove and Replace the Air Filter

Once realizing the air filter was saturated with gas, simply remove the housing cover, then grasp and pull the filter out, being cautious not to spill excess fuel. With the filter removed, take a moment to inspect the housing for debris buildup or clogs that inhibit airflow.

A clean, properly fitted replacement filter slides into place, locks the cover on, and restores airflow for improved performance. Regular filter changes maximize airflow, prevent contamination from entering the engine, and keep your lawnmower operating smoothly for seasons to come.

Repairing Surging Engine RPMs by Cleaning the Carburetor

Repairing Surging Engine RPMs by Cleaning the Carburetor
Repairing a surging engine starts with a thorough cleaning of the carburetor, which is crucial for proper fuel and air mixing. To clean the carburetor, you’ll need to completely disassemble it, using carburetor cleaner on all passages and jets, being cautious around delicate openings, and considering an ultrasonic bath for the most comprehensive cleaning possible.

Importance of a Clean Carburetor

You’d be wise to clean that carburetor if you want your mower running smoothly again. I know it seems daunting to take apart, but a thorough cleaning really is the best remedy for surging RPMs in most cases.

  1. Remove the carburetor and disassemble it completely.
  2. Use carburetor cleaner to thoroughly clean all passages and jets.
  3. Carefully reassemble, replacing any worn gaskets or seals.

A clean carburetor ensures proper air-fuel mixture and efficient combustion for optimized engine performance. Regular carburetor maintenance and inspection prevents many issues down the road.

Steps to Disassemble and Clean the Carburetor

To clean the carburetor, you’ll need to carefully disassemble it and use carburetor cleaner on the jets, openings, and passages.

Start by disconnecting the fuel line and removing the carburetor from the engine.

Separate the carburetor bowls and floats, exposing the main jet and needle valve. Use compressed air and wire picks to clean out clogged passages before spraying all components with carb cleaner.

Let them soak before wiping dry. Inspect the seals, gaskets, springs, and replace if worn.

Reassemble using your notes, adjusting screws per spec. Proper cleaning restores performance, but consider ultrasonic cleaning for a thorough interior de-gunking.

Considerations for Ultrasonic Cleaning

Rather than disassembling the carburetor yourself, an ultrasonic cleaner can thoroughly clean the carb without damaging any delicate openings. Ultrasonic cleaning vibrations remove grime from the smallest passages. Opt for a cleaning solution formulated for carburetors to avoid corrosion.

Ensure metal and rubber components are compatible. Wear eye protection as the agitation can fling debris.

Consider professional cleaning for the pneumatic governor’s delicate springs under the engine shroud, especially after a gasoline spill fouls a Briggs and Stratton 675 engine’s fuel pump. The ultrasonic cleaning option prevents potential damage during disassembly while still effectively cleaning the carburetor’s internal components.

With proper precautions, it’s an excellent troubleshooting step before reassembling the carburetor.

Understanding and Adjusting the Governor

Understanding and Adjusting the Governor
If your lawnmower is experiencing surging RPMs, the governor is a key component to examine. The governor maintains engine speed by controlling throttle position through a spring connected to the carburetor.

Inspecting its operation and adjusting the spring tension can help resolve RPM fluctuations. To properly address governor issues, you’ll need to determine if you have a pneumatic type that uses an air vane or a mechanical style with gears before adjusting or replacing its spring.

Role of the Governor in Maintaining RPMs

Pneumatic and mechanical governors stabilize your mower’s RPMs using air vanes or gear mechanisms. Sluggish, sticky, or damaged governor springs allow RPM fluctuations and surging. When troubleshooting RPM surges, inspect the governor spring’s tension and positioning.

Replace stretched springs to restore proper tension. Pneumatic governors have springs under the shroud, while mechanical types mount near the carburetor. Adjusting the governor spring tension restores steady RPM regulation. With a basic understanding of the governor’s role in maintaining RPMs, you can diagnose and resolve fluctuation issues.

Types of Governors (Pneumatic Vs. Mechanical)

You’ve got a pneumatic governor if your mower’s engine uses an air vane to maintain RPMs, while a mechanical governor uses gears and levers for the same purpose. Pneumatic governors rely on airflow to control engine speed but are prone to sticking and surging issues from dirt buildup.

Mechanical governors use linkages and springs for more precise control but require proper lubrication and adjustment to minimize slack in the system. Following the manufacturer’s service guidelines for cleaning or replacing worn governor components is key to optimizing lawnmower performance and engine RPM stability.

Adjusting or Replacing the Governor Spring

To resolve surging engine RPMs, inspect the governor spring tension and position to ensure proper regulation of engine speed. If the spring is stretched or improperly positioned, it cannot properly control the throttle.

Loosen the spring’s retaining bolt, adjust tension per the manufacturer’s guidance, and verify RPM stability. Replace worn springs for long-term performance. Proper governor spring adjustment maintains throttle control, stabilizes engine RPM, and prevents surging.


Lawn mowers with surging engine RPMs can be a frustrating issue, but luckily there are several steps you can take to fix the problem. On average, a lawn mower needs routine maintenance every 25 hours of use, and neglecting this can cause the engine RPMs to surge.

Spark plug and fuel issues, air intake and governor problems, and saturated air filters should all be examined when diagnosing this issue. Cleaning the carburetor, adjusting or replacing the governor spring, and understanding how the governor works are also critical steps for resolving the surging RPMs.

By following these troubleshooting and repair tips, you can restore your lawn mower to a reliable working condition and get back to enjoying your lawn and garden.

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Mutasim Sweileh

Mutasim is a published author and software engineer and agriculture expert from the US. To date, he has helped thousands of people make their yards lush and thick.