You’re riding along on your lawn mower when you notice it’s not giving you the power it once did. It keeps bogging down and the engine isn’t running strong.
Anytime your engine isn’t performing as it should, you must identify and fix the problem before it develops into a larger problem. When you’re dealing with an engine, a repair can get pretty expensive if you don’t address it right away.
A riding lawn mower will lose power when the engine doesn’t get good airflow and fuel flow, or the engine runs hot.
This can be the result of a low engine oil level, clogged air passageways, plugged air filters, a dirty carburetor, and restricted fuel components.
A riding mower may also begin to lose power when the engine is under load due to a plugged mower deck or too fast of a ground speed for the mowing conditions. Keep reading for more details.
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Follow all safety instructions provided in your equipment operator’s manual before diagnosing, repairing, or operating. Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.
14 Reasons Your Riding Lawn Mower is Losing Power
Plugged Air Filter
Experiencing a loss of power causing your riding mower to run sluggish can be something as simple as a plugged air filter. Because mowing is a dusty job with your mower kicking up grass clippings and dirt, the air filter can become plugged with these items.
The air filter must be replaced or cleaned regularly to ensure air is able to pass through the filter. When this doesn’t happen, the filter can become plugged and keep your engine from getting the air it requires to perform at its best.
It is good practice to replace your air filter with a new one annually. Then, clean it several times throughout the mowing season. You may have to change and clean your filter more frequently if you are mowing in very dusty conditions.
How to Clean Your Riding Lawn Mower Air Filter
These instructions are for cleaning a paper-style air filter. Find instructions for cleaning other types of filters here.
- Remove the cover from the air filter housing. This is often held on by clips, knobs, or wing nuts.
- Carefully remove the air filter so you don’t allow dirt to fall into the air intake.
- Clean out any dirt that remains in the air filter housingusing a dry clean rag.
- Tap your air filter against a hard surface to knock as much dirt loose and out of your filter as possible.
- Hold your filter up to a light source. If you can see light shine through the paper, go ahead and reuse the filter. If you can’t or the filter is damaged or covered in oil, replace it with a new air filter.
- Install the filter and reattach the air filter cover.
Old Fuel
Your riding mower may begin to run sluggish when it is running old or bad gasoline. Gasoline begins to break down and becomes less effective after 30 days.
In addition to breaking down, ethanol and moisture in the fuel can leave behind gummy deposits that restrict fuel flow. A power loss will be experienced when the engine doesn’t get enough fuel.
If you find old fuel in your riding mower, drain the fuel tank and fill it with fresh gasoline. Most gas-powered riding mowers require unleaded gasoline with a minimum octane rating of 87 and a maximum ethanol content of 10%.
Add a fuel additive like Sea Foam Motor Treatment to stabilize the gas, reduce moisture in the fuel and clean the fuel system.
Because gasoline breaks down so quickly, it’s best to use fuel within 30 days. If you are unable to consume it within this time, add a fuel additive. I like to add Sea Foam to every tank of fuel.
You can find out more about why I like Sea Foam in this guide and the effects of ethanol on your lawn mower in this guide.
Plugged Fuel Filter
A fuel filter strains the fuel as it comes out of the fuel tank to keep dirt and debris from entering the fuel system. When the filter isn’t changed out regularly, the filter will become plugged preventing fuel from passing through the filter.
It is good practice to replace your fuel filter annually when performing your routine riding mower maintenance. This filter is an inexpensive part that can prevent fuel supply issues and significant engine damage if it fails to strain dirt efficiently.
To replace the filter, shut off the fuel flow using the fuel shut-off valve on the mower or fuel pinch pliers if your mower doesn’t have a shut-off valve. Pull the filter out of the fuel lines and install a new filter.
Pay attention to the arrow on the side of your filter. The filter must be installed with the arrow pointing in the direction of the fuel flow. The arrow should be pointed toward the carburetor and away from the fuel tank.
Clogged Fuel Line
The gummy deposits mentioned previously from running old gas can clog the fuel lines. Check for a clog in your riding mower by stopping the fuel flow and removing the end of a section of the fuel hose and placing it in a container. Start the fuel flow to check for good flow out of the fuel line.
When you find a clogged fuel line, stop the fuel flow and remove the section of the line from the riding mower. Spray carburetor cleaner into the line. This is to help loosen up the clogs. Blow compressed air through the line to free the obstruction.
If you cannot remove the blockage or you notice your line is dry and cracked, replace it with a new fuel line of the same length and diameter.
Dirty Carburetor
Your carburetor is an important component of your mower. It regulates the correct amount of fuel and air allowed in the cylinder to form combustion.
The substances left behind by running old fuel can collect in your carburetor preventing it from providing the fuel needed to run. When this happens, the dirty carburetor can cause your riding mower to experience a loss of power.
Clean a carburetor that isn’t allowing fuel to get to the cylinder. Before you tear your carburetor apart, remove the air filter and spray carburetor cleaner into the air intake.
Start your engine to see if it will run. If it runs, but it won’t stay running, you need to clean your carburetor. Refer to the article to find step-by-step instructions to clean your riding mower carburetor.
Bad Spark Plug
A fouled spark plug can cause an intermittent spark that can cause a loss of power. Inspect your spark plug for signs of carbon, dirt, and oil buildup on the tip. If you find a dirty or damaged spark plug, I recommend replacing it with a new one to ensure you’re running a good plug in the mower.
Alternatively, if it’s only dirty and not very dark in color, you can attempt to clean it with a wire brush and reuse it.
Low Engine Oil Level
When the engine oil level in your riding mower’s crankcase is low, you’ll experience a loss of power. You could be low on oil if you didn’t add enough oil into the crankcase during your last oil change.
It could also be the result of an engine oil leak or from burning oil due to running the wrong oil viscosity.
You never want to run a riding mower with a low engine oil level. If you do and it’s not caught soon enough, significant engine damage can result in a large repair bill or even an engine replacement.
Engine oil is required to keep the internal engine parts lubricated. When there is a lack of lubrication, friction builds from the moving parts and creates extreme heat. This can cause your riding mower to overheat and smoke from burning oil and melting parts.
Check your engine oil level before each use of your riding mower as a precaution. I understand it’s one more step in your busy schedule, but it doesn’t take long and can help you catch oil leaks and engine problems before they develop into significant problems.
To check your engine oil, remove the dipstick and use a clean rag to wipe the oil off the stick. Replace the dipstick and then remove it. Check the oil level. The oil needs to be at the full level on the dipstick.
If it is not, add fresh engine oil until it is full. Do not overfill it or you’ll run into more problems.
If you continue to have problems with your engine after you refill it to the full level, you should have the engine diagnosed by an experienced small engine mechanic. A low engine oil level may have caused internal damage that can’t be fixed by adding a little fresh oil.
Too Much Engine Oil
Overfilling the crankcase with engine oil will cause your engine to smoke. Increased pressure builds as a result of too much engine oil and oil can be pushed into the cylinder through the valve train.
When this happens, a bluish-white smoke is emitted when the oil burns in the cylinder.
This thick cloud of smoke can plug your air filter causing running issues because your engine isn’t able to get the clean air it needs. Check your air filter and your spark plug, and clean or replace them if needed.
Continuing to run your riding mower with too much oil can cause seal damage, the engine to hydro lock, and a bent piston rod. Correct an engine with too much oil by removing a little oil. You can do this by using an oil evacuator, a drain plug, or even a turkey baster.
Remove a Little Engine Oil
You can remove the oil by loosening and quickly tightening the drain plug to only allow a little oil out of the engine. You can also remove oil from the oil filter or out of the oil fill area using a turkey baster or oil evacuator.
Dirty Engine Cooling Fins
The cooling fins are essential to keeping the air around the engine cool. Just like you need to remove debris from collecting around your engine so your engine doesn’t overheat and experience a loss of power, the same is true of your cooling fins.
The fins can become plugged with mud and grass clippings inhibiting the air circulating around the engine block. The fins are used to dissipate heat. Clean the debris from the cooling fins and replace any broken fins.
Blocked Air Passageways
Your engine needs to be kept cool to prevent it from overheating and losing power. Make sure your engine has good air circulation by removing any grass clippings, dirt, and debris that may be collecting around your engine.
Remove all the debris that has been collected under your engine shroud.
Fast Ground Speed
Trying to complete your mowing task quickly so you can move on to relaxing for the day sounds like a good idea, but it may be the cause of your riding mower losing some power.
Mowing your lawn at a fast speed can put an extra load on your mower when mowing thick, wet, or tall grass.
Operate your riding mower at a slower speed to account for your mowing conditions so you put less strain on the mower. This includes slowing down when mowing on an incline at fast speeds as this also affects the engine power required.
Cutting Wet, Tall, or Thick Grass
Avoid cutting grass that is damp or wet. Wet grass causes your engine to work harder. It is more susceptible to clumping and sticking to the underside of the mower deck. For the best cutting performance, mow your lawn when the grass is dry.
It’s best to keep your grass cut at a manageable length by regularly cutting your grass. If your grass does get very tall, your mower can bog down when attempting to cut it. As much as you try to keep your grass mowed, there are times when the grass does get tall.
When mowing tall grass, you should double or triple-cut your lawn for the best results. Do this by adjusting the mower deck to its highest setting for the first cut and then lowering the cutting height for the next cut.
Plugged Mower Deck
The area under the mower deck must be kept clean and free of debris to avoid overworking the engine and experiencing a loss of power. When the riding mower blades are rotating under the mower deck, they should be able to move freely.
A packed mower deck puts extra strain on the engine when it is required to work harder to turn the blades through the debris. Keep your mower deck clean by regularly scraping it to remove debris.
This is not only good for your engine, but also for your riding mower’s cut quality.
Dull Mower Blades
What further impacts the loss of power a riding mower receives when the deck is packed are dull lawn mower blades. A plugged mower deck requires additional engine power, but adding dull mower blades makes it a lot worse.
Check your blades and sharpen or replace them if needed. You can find more information on inspecting your blades and the sharpening process here.
Still Having Problems With Your Riding Mower?
As a lawn mower owner, when you own it long enough, you are going to run into different types of problems. This may include problems where your mower is smoking, cutting unevenly, losing power, not starting, leaking fuel, and more.
Check out this handy guide including charts for common mower problems and solutions:
Common Riding Lawn Mower Problems & Solutions.
If you are unable to fix your mower or don’t want to attempt a more complicated repair, have your local lawn mower dealership or repair shop for assistance.