7 Reasons Why Lawn Mower Revving Up and Down

When it’s time to mow the lawn, you want your lawnmower to perform properly. It will develop issues over time. Your lawnmower may run too fast or slow.

There are a few different things that could be causing your lawnmower to rev up and down. It’s possible that the problem is with the insufficient airflow, the spark plugs, the air filter, the fuel filter, or the carburetor.

You will gain an understanding of why the engine on your lawnmower revs up and down, as well as how to fix the issue by going through this article.

Why Is My Lawnmower Revs Up and Down?

When your lawnmower revs up and down, it’s because the governor isn’t able to keep the speed constant. The problem could be caused by a lack of fuel or airflow. It could be due to an issue with the spark plug, air filter, contaminated fuel, or unadjusted carburetor.

You need to inspect each of these components to see whether or not any of them are broken or clogged. If none of those things seem to be the problem, it may be time to take your lawnmower to a professional to have it checked out further.

7 Reasons Behind Lawn Mower Revving Up and Down

The following is a quick overview six most common reasons why lawnmower revs move up and down, as well as the fixes for those problems.

1. Lack Of Fuel

If the lawnmower is revving up and down for no apparent reason, it is likely due to a lack of fuel. If the fuel tank is low or empty, then the engine will not be able to run at a steady speed. This can cause the engine to rev up and down as it tries to find a consistent fuel supply.

The Fix

Check the fuel filter and fuel lines for any blockage or debris. Make sure the fuel tank is full as well.

2. The Spark Plug is not Firing Correctly

An engine that revs too high or too low could be the result of a spark plug that is not firing correctly. This may be the result of a faulty spark plug or a spark plug that is just dirty.

The Fix

Make that the spark plug is not worn out or damaged. Spark plugs should be changed whenever they show signs of wear.

It’s important to inspect the spark plug’s gap and make sure the electrode isn’t touching the ground strap. Verify that the space between the blades is appropriate for your lawnmower.

Be sure to check the spark plug wire for any rust or damage. You should change the wire if it’s frayed or corroded.

3. Problems with Airflow

A simple problem with the lawn mower’s airflow could be the cause of its hunting and surging.

Blocking the airflow that the engine needs to function, even intermittently, might reduce its performance. The engine may speed up unexpectedly when the obstruction is removed.

The Fix

A clogged air filter is a common cause of this issue, so double-checking will help resolve the problem.

Also, make sure the gas cap has a vent. Both can hinder or completely halt airflow, and resolving either one will do the trick.

4. The Spark Plug Gap is Incorrect

Sometimes the distance between the electrodes on the spark plug is inaccurate. The distance between the electrodes on the spark plug is referred to as the spark plug gap.

The engine could rev more quickly or less quickly depending on whether the gap is too big or too narrow.

The Fix

To fix this issue, you need to adjust the spark plug gap. This can be done by using a feeler gauge and adjusting the gap to the manufacturer’s recommended setting.

Depending on your lawnmower, this can be done by loosening the spark plug and adjusting the gap until it fits snugly between the two electrodes. Once the gap is set, you can then tighten the spark plug back into place.

5. Clogged Air Filter

If the air filter is clogged, it might restrict the flow of air to the engine, which can cause the engine to rev more quickly and less often than normal.

The Fix

Ensure the air filter is clean. Reduced airflow from a clogged air filter might lead to erratic engine performance. Replace a badly broken air filter. A properly cleaned normally blocked air filter can run smoothly.

Steps to clean:

  • Disconnect the spark plug cable. Maintenance and repair require appropriate safety precautions. This prevents harm.
  • Remove the engine air filter cover.
  • First, hand-wash the foam filter. Dry it. Apply a light engine oil coating to the foam filter after drying. It keeps dirt and grease out of the carburetor.

6. Carburetor is Out of Adjustment

Another reason is carburetor is not calibrated properly. If the carburetor is not adjusted correctly, it might cause the engine to rev erratically.

The Fix

Most lawnmowers’ two screws can be adjusted to change the carburetor setting.

While the other screw regulates the ideal lawnmower speed, the first one adjusts the fuel-air mixture. If you don’t know much about the system, you should read the instruction manual.

Be sure to adhere to it. Before running the machine for a while, tighten the screw as usual. The screw position should then be adjusted in accordance with the engine’s needs.

7. Contaminated Fuel

If the fuel is contaminated, it might cause the engine to rev unevenly, which can be quite dangerous.

It is possible for contaminated fuel to have dirt, debris, or even water in it, all of which might make the engine behave unpredictably.

The Fix

Remove the fuel filter and drain the tank. Make sure the gasoline line is clear of any obstructions. Refill the tank with new, filtered gas and look for leaks.

You should check the air filter and clean or replace it if necessary. The spark plug should be inspected for fouling and replaced if necessary.

If the carburetor has any debris, dirt, or worn parts, you should clean it or replace it. If required, tweak the carburetor settings.

Frequently Asked Questions (FAQs)

What makes a lawn mower surges up and down?

A clogged fuel line is by far the most typical cause of a surging lawn mower motor, although there are others: Weak gas. A faulty spark plug. Damaged or clogged carburetor.

What causes engine over revving?

Missing a gear while shifting causes most over-revving. A rev restriction cannot prevent engine overrevving in a manual car that mistakenly downshifts.

What does it mean when your RPM keeps revving?

If your lawn mower revs up when idling, your fuel pressure is probably faulty. Your car’s fuel pressure is unregulated due to a broken regulator, injector, or pump.

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