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Why Is My Riding Mower So Slow?

A lawn mower is a machine for cutting grass. Lawn mowers are used on lawns, fields, and gardens to cut grass. They usually have a motor so they can do the job without human power. 

Some of the most common forms of lawn mowers are gas or electric-powered riding mowers, which are mainly used on large-scale professional groundskeeping jobs where the ground is not too uneven. 

The blades of the machine are mounted on the underside of the machine, and most modern machines are powered by an internal combustion engine. These most durable outdoor appliances can still have trouble running from time to time. 

There are a lot of reasons why lawn mowers might start to run slower or even stall out. We’ll be discussing the possible causes and the fixes to solve this problem. Before you give up on your old machine, try these solutions first.

A damaged riding lawn mower in the lawn
Riding Lawn Mower

Reasons why a riding mower runs slow:

  1. Faulty drive belt
  2. Clogging in the fuel line, gas cap, or in the carburetor
  3. Over tension in the drive belt
  4. Type of fuel blend
  5. Damaged pulley spring
  6. Problems with throttle and governor
  7. Stuck Speed Shift Lever

Faulty drive belt

The main function of the riding mower is to cut grass over large areas, such as fields and golf courses, in a short amount of time. It does this by using two blades rotating at high speed with the help of an engine to keep it going. 

A faulty drive belt can cause the engine to run slower, thereby reducing power transmission from one pulley to another. The upper drive belt is connected to the transaxle pulley and the belt guide. 

For a variable-speed riding mower, it might be connected to the variable-speed pulley. If it is not in good condition, the mower will run slowly. This is a simple guide on how to replace faulty drive belts.

  1. Detach the bolts to detach the cutting deck from the lawn mower.
  2. Disconnect the power source or the battery.
  3. Remove the spring from the anchor bolt and move the transaxle pulley.
  4. Disconnect upper drive belt of the unit.
  5. Install the new upper drive belt.

Clogging in the fuel line

Clogging in the fuel line, gas cap, or in the carburetor causes the riding mower to run slow. lawn mower engines might get clogged up with carbon particles. 

The fuel injectors get clogged by carbon buildup, the gas cap gets clogged by liquid buildup, and the carburetor can also get clogged by liquid buildup. Carbon is a natural combustion engine byproduct that builds up over time.

Carbon buildup from engine misfire will clog up your fuel injectors and make it difficult for fuel to reach your engine. This causes a decrease in performance because you can’t burn as much usable fuel. 

This also leads to other problems such as a decrease in power and an increase in emissions.

Clogging in the gas cap

The gas cap is usually a metal or plastic container that is attached to the top of the fuel tank on a lawn mower. The gas cap blocks any debris from reaching the fuel inlet and causing a blockage. 

This will cause a vehicle to sputter, stall, and lose power. lawn mowers typically produce a gurgling sound when they run out of gas. 

If you do not hear this sound, it may be an indication that there is blockage in your lawn mower, such as dirt or leaves that have been sucked into the system. 

This can be fixed by removing these objects from your lawn mower and then running it again. You can clean a gas cap with a hose to remove any dirt and other contaminants that may have been accumulating in the mouth of the gas tank. 

You should also use petroleum-based lubricant spray on the threads of your cap before you reinsert it so you don’t have any problem unscrewing it later on.

Clogging in the carburetor

As one of the most important parts of any engine, the carburetor is responsible for distributing fuel to the engine. If it malfunctions, your riding lawn mower will run slower.

A Faulty Carburetor
A Faulty Carburetor

The engine is the power source that converts fuel into motion. Gasoline deposits inside the carburetor can clog fuel and air passages, causing engine performance to decrease or even stop altogether. 

The engine will have problems if it does not receive enough oxygen to burn fuel properly. When the carburetor clogs, it restricts the flow of air, and the exhaust gases are not burning quickly enough so they are forced out in a backfire or an overheat.

To fix this issue, you can take off the spark plug cap to make sure that the engine and the mower doesn’t backfire. You should also drain the fuel to remove any residue or buildup in the carburetor.

The first step is to remove the spark plug cap to make sure there is no ignition happening. Next, drain all the fuel from your carburetor before replacing it with fresh fuel. Finally, replace your carburetor filter and you should be good to go!

Over tension in the drive belt

One of the most common causes for a riding mower running slow is tension in the drive belt. If you do not see any debris or other obvious problems, check the tension of the belt to see if it has become over-tensed. 

If it has, then loosens it by turning your fingers clockwise on the belt until you find a spot that feels loose enough to spin freely. Then tighten it back up by turning your fingers counterclockwise on the belt until there is resistance.

Type of fuel blend

There are many types of fuel blends that can be used in a lawn mower, but not all are created equal. Some are much better than others when it comes to their effects on the lifespan of your engine. 

These variations usually only affect the larger vehicles, such as cars and trucks, but can be detrimental to smaller and more delicate engines like those on riding mowers. 

When it comes to choosing the right type of fuel, you need to consider what your engine needs. Not all fuels are created equal so being sure you have the right blend is essential. 

So, you should use the proper blend of fuel to get the full performance.

Damaged pulley spring

The pulley spring in the riding mower is what makes your engine run smoothly. If it is damaged, it will cause the mower to run slow and unevenly.

Damaged Pulley spring of a lawn mower
Damaged Pulley Spring

Damaged pulleys can happen for a variety of reasons, including impacts from rocks or other debris, improper installation, corrosion from exposure to moisture or salt, or through normal wear and tear. 

If you notice your mower is not moving as well as it typically does, it’s important to have a professional inspect the machine before using it again.

If a pulley spring becomes damaged, it can be difficult to replace it. One way to identify the problem is by looking at the idler pulley, which should have a spring that is no longer attached. 

The first step in replacing the pulley spring is to remove the battery and remove the cutting deck and spark plug. Remove the idler pulley spring. Install the new one and put back in the chain saw’s battery, cutting deck, and spark plug.

Problems with throttle and governor

A throttle, also known as a throttle valve, regulates the amount of air that flows into the cylinder on an engine. The governor regulates the speed of a riding mower by releasing or restricting fuel supply to it. 

When these two components are working together smoothly, the machine operates at the desired speed.

The governor spring that tensions the governor vane can break or lose its tension over time which may make it difficult to keep the machine at a constant speed. The throttle can stick open which can cause an engine to run very slowly.

When a problem occurs with the throttle, the governor spring, or the governor vane, it may lead to a riding mower running slow, stalling at idle speed, or not starting at all.

To adjust the governor, you should undo the screw on the bottom of the arm and set it so wide open. Then turn the lower clip clockwise. This will set the governor shaft on top of govern which should have been previously placed on it to fix their height difference.

Stuck Speed Shift Lever

It is very important to maintain the proper speeds for riding mowers. When the speed shift lever is used improperly, it may cause the mower to run slow, which can result in a loss of power and transmission slip. Dirt, debris and other tiny particles can also find their way into the engine’s oil which may clog up the filter. This could lead to trouble with lubrication.

Luckily, you can make a few small adjustments to your speed shift lever to get it working again.


A riding mower is an excellent way to maintain your yard at a fraction of the cost of hiring someone else. However, if you come across any problems with the engine, you will need to know how to fix them before you can get back to cutting your grass. 

Fixing a riding mower that runs slow can be a difficult task. You check the fuel supply. If it is not providing enough gas to the engine, then you will need to replace faulty drive belt, unclog the fuel line, and replace the gas cap. 

In some cases, you will need to fix governor as well. Replacing faulty components will help with mower performance and make it work at its best.

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