A Lawn Mower Troubleshooting Guide




Honda 663040 GCV170 Self-Propelled Lawn Mower

Honda 663040 GCV170 Self-Propelled Lawn Mower

How to troubleshoot lawn mower will help owners to quickly identify the problem and apply the appropriate solution as mowers can fail for many reasons. Let’s look at some of the most common reasons why your lawn mower is having problems.

  • Lawn mower won’t start
  • Losing power in the middle of mowing
  • Mower is releasing smoke
  • Lawn mower is leaking gas
  • The mower blade will not turn

The above are just a few of the most common problems you could experience with your lawn mower. If you notice any of these issues, you should fix them immediately. If you let the issue continue without repair, you could ruin the mower and have to replace it with a new one.

We will examine each of these problems individually.

Lawn Mower Won’t Start

Dirty Lawn Mower Carburetor

Dirty Lawn Mower Carburetor

You have probably experienced this issue every spring when you are mowing the lawn for the first time. Let’s look at some of the possibilities for this issue.

  • Bad Gas. It is possible that the gas in the tank is bad and was not drained out when the mowing season ended the prior year. Gas gets stale after 30 days and can make the engine difficult to start. The gas used for mowing probably did not contain any fuel stabilizer. If this is the case, just drain the bad fuel out of the tank and replace it with fresh gas. Try starting the mower. If successful, problem solved. If not, continue reading. If the gas did contain a fuel stabilizer during storage, you should not experience any starting problems with this issue. It is something else.

Note: It is recommended that you put a fuel stabilizer into the gas can to keep it fresh.

  • Dirty Air Filter. It is possible that the air filter is dirty or has some debris in it. This can cause engine to sputter, lose power, won’t start, increased fuel consumption, and black smoke blown out of the exhaust. If you experience any of these issues, this is a sign that the air filter is dirty and needs to be replaced. Replace the air filter with the model mentioned in the owner’s manual. Try starting the mower. If successful, problem solved. If not, read on.
  • Dirty Spark Plug. If you should experience any of the following issues, the spark plug may be the cause. 1). The engine requires repeated attempts to start or won’t start at all. 2.) The engine misfires or runs rough. 3). Starts briefly but stalls shortly after. 4). Increased fuel consumption. Check the spark plug itself as see if it appears damaged, corroded or has carbon build-up.

Solution: Replace the spark plug with a new one according to the owner’s manual. Try starting the mower. If successful, problem solved. If not, read on.

  • Dirty Fuel Filter. A dirty fuel filter may not provide enough fuel to reach the engine. It is bad if you observe any of the following: 1). poor engine performance, 2). hard starting and stalling, 3). random misfire or rough idle. Replace the fuel filter with a new one according to the model mentioned in the owner’s manual. Try starting the mower. If successful, problem solved. If not, read on.
  • Bad Carburetor. If the carburetor is bad, here are some signs: 1). mower has trouble starting, 2). engine starts but stalls when cutting the lawn, 3). engine runs rough when mowing, 4). black smoke is seen coming out of the muffler, 5). and an increase in fuel consumption. There are two options: clean the carburetor or replace it with a new one. Try cleaning the carburetor first if you have all the tools to do the job. If not, take it to the local repair shop. Replace the carburetor with a new one yourself according to the owner’s manual or have the local repair shop do it for you. If the mower starts, the problem is revolved. If not, you have a more serious problem.

If after doing all of the above, and you still have a problem with the mower, there is some other serious problem your mower is experiencing. Your options are: take it to the repair shop for an estimate of the repair or just get a new mower.

Video: Fixing The Mower Won’t Start Problem

Below is an excellent video on fixing a mower that will not start. Take a look!

Losing Power In The Middle of Mowing

If you are experiencing a loss of power loss as you are mowing, there are a couple of reasons for this. We mention them below.

  • Dirty Air Filter. Clean or replace the air filter according to the owner’s manual. Cleaning or replacing the air filter should bring noticeable improvement. If not, read on.
  • Dirty Spark Plug. Check to see if the spark plug is dirty. If so, clean it. Replace the spark plug according to the owner’s manual if you found any damage or rust.
  • Cutting Tall Grass. Just raise the cutting height on the mower.
  • Build Up of Clippings Under The Deck. Clean the underside of the mower deck to remove any dirt, grass clippings and debris. You should clean the deck after each mowing session. A build-up of this debris can cause the engine to run harder which could make the mower to lose power.
  • Dull, Bent or Loose Blade. If the mower blade is bent or loose it can cause loss of power. The reason is the mower has to use more engine power to cut the grass. Solutions: 1). Sharpen dull blades according to the owner’s manual. 2). Tighten any loose mower blades using the proper tool. 3). Replace the mower blade or blades every 2 years. 4). If you should mow over obstacles like rocks or other items in the yard, check the blade for damage. 5). Sharpen the mower blade at the end of the mowing season.

After applying any one of these fixes, your mower should improve its performance. If not, you may have a more serious problem that will need to be checked by the local repair shop.

Mower Is Releasing Smoke

Dirty Lawn Mower Air Filter

Dirty Lawn Mower Air Filter

There are a couple of reasons why your mower is smoking when cutting the grass. First, it is possible that you may have overfilled the oil chamber. Some oil could have leaked into the exhaust muffler. The mower is simply burning off this excess oil. Mowing on a steep slope can also cause some smoking to occur. Second, if you should see colored smoke, have issues in keeping the mower running, it is a more serious problem. You will need to take the mower to the repair shop.

Let’s look at what you can do to fix this problem.

  • Check the Air Filter. Inspect the air filter for any dirt or debris. Clean it. If too dirty, replace it with a new one.
  • Check the Oil Level. Be sure the oil is at the proper level. If overfilled, the mower let’s out the excess oil and causes burning. Be sure you have the proper grade oil and type in the crankcase.
  • Check the Angle You Are Mowing. If you mow in angles greater than 15 degrees, it can cause the lawn mower to smoke.
  • Cracked Crankcase. If the smoking issues persist, it is possible that the oil seals in the engine lubrication system or around the pistons is the problem. It is possible that the crankcase is cracked. To fix these problems, only a pro can do it. Take it to the local repair shop.
  • Carburetor Needs Cleaning. It’s possible that the carburetor is dirty and needs cleaning or needs adjusting. Begin by cleaning the carburetor. Check the owner’s manual for how to adjust the carburetor. In some cases, you may have to replace the carburetor with a new one.
  • Types of Smoke Colors. If you see black smoke, or you see blue or white smoke after the mower has been running for 15 minutes, you may have an engine problem. Wait until the engine cools down and check the air filter. If it’s clogged, it needs to be replaced with a new one. This should fix the smoking issue.

Lawn Mower Is Leaking Gas

Leaking gas is a common problem with lawn mowers as they age. We will share some of the most common reasons why your mower is leaking gas. Please note, that some of these solutions may not pertain to your mower. We present them is case it may help others.

  1. Carburetor Bowl. You will need to look at the carburetor. This is the place where the fuel is stored after it leaves the tank. Look around the bottom of the carburetor as this is the bowl. You should see a thin o-ring that goes between the base of the carb and the bowl. This is the most common area of leaking. The o-ring is going from hot to cold temperatures and this stress can cause the o-ring to become hard and lose sealing strength and needs to be replaced. Replace the o-ring gasket with the correct make, model and spec number. Go to the local shop to get a replacement. After replacing the o-ring gasket, check for no more leaks.
  2. Float Is Stuck. Look at the opening of the carburetor. If you see a fuel leak that is coming from the intake port, the float could be stuck. When the float gets stuck, it will not shut off and will allow fuel to run out of the carb. You need to determine why the float is stuck. You may have to take the mower to your local shop to check it out.
  3. Stuck Float Needle. After looking at the float, now look at the part in the carb called the needle. The needle keeps gas flowing to the bowl with the floats help. Sometimes the needle does get stuck. You may have to take the carb apart to determine why the needle keeps getting stuck. This may also mean you have to replace the carburetor with a new one. A quick fix: Take the end of a hammer and gently hit the side of the carburetor to free up the needle. This may work a couple of times. Eventually, you need to find out why the needle is sticking.
  4. Bad Fuel Lines. Look at the fuel lines coming out of the tank for any dry, cracked, or rotted lines. If found, they must be replaced.
  5. Fuel Tank Is Bad. It is possible that the fuel tank is the cause of the leaking. If your mower is old and has a steel tank, inspect it for any small rust hole. If you have a plastic tank, check the seams where the plastic is molded together for any leaks. If found, replace the tank or get a new mower.
  6. Fuel Valve. Look at the fuel tank and inspect the fuel valve that is at the bottom of the tank. These are either plastic or steel. These valves are prone to leaking. If found, replace the fuel valve.
  7. Fuel Filter. Another reason for smoke is due to the fuel filter not being changed. You will need to replace the fuel filter or clean it periodically to prevent leaking fuel.
  8. Fuel Pump. The plastic fuel pump can break down and deteriorates due to the fuel. As this material rots over the years, leaks develop. If this is the cause, you will have to replace or repair the fuel pump.
  9. Gas Cap. Inspect the gas cap to ensure it is venting and sealing properly. As you mow around the yard, gas is sloshing around in the tank and can leak out of the top of the tank where the gas cap is secured. If you should see a wet spot around the cap area after splashing the fuel around, replace the gas cap with a new one.
  10. The Primer Bulb. Some of the older lawn mowers have a primer bulb on the side of the mower. The primer bulb can leak fuel when the bulb fills with fuel. Sometimes the primer bulb becomes weak or brittle over time. If this is the case, replace the primer bulb with a new one. Check the owner’s manual for instructions on how to do the job and what model bulb part you need. If you don’t want to change the bulb, just take the mower to the local repair shop to do the repair.

The Mower Blade Will Not Turn

Homeowners with lawn mowers may have experienced at some time or another the blade will not turn. There are a few reasons for this problem. We will discuss some of them to see if any can help you fix your blade issue not turning.

  • Over Tightening the Blade. The lawn mower blade is to be loose enough to slip when they should hit a solid object. This protects the engine and the blade from damage. If you recently changed the blade, you may have overtightened the blade. Check the owner’s manual for the proper tightening of the blade.
  • Bolt Was Threaded The Wrong Way. If you threaded the blade bolt the wrong way this could also be a reason why the blade won’t turn. On walk-behind mowers, bolts are right-hand threaded. Which means to loosen it, you must turn it to the left. Check to ensure that the bolt was threaded the wrong way.
  • The Undercarriage Is Dirty. Check the undercarriage of the deck to determine if any debris is caught around the blade. If there is a build-up of debris or other obstacles, clean the deck and remove the obstacles. Start the mower to determine if the blades are moving. If yes, problem solved. If no, you have other issues.
  • Seized Engine. This occurs when you fail to put oil in the crankcase or the mower is sitting for a long time in wet conditions. This causes the piston in the motor to seize. To fix this, you might be able to free the piston by removing the spark plug and manually rocking the blade. Then spray a generous amount of lubricant or penetrating oil into the spark plug hole. Wait 10 minutes before rocking the blade. If you feel the blade starting to turn, spin it a few times slowly in its normal direction of rotation. Place the spark plug back in and try starting the mower.
  • Blade Obstructions. There could be some obstruction that is blocking the blade from turning. Check to see if a small rock is lodged between the top of the blade and mower deck. Another reason is when mowing you ran over a stump or large object and the blade could be bent. When checking for these issues, remove the spark plug boot, put on leather gloves and investigate. If the blade is bent, replace it with a new one. After the blockage is removed, try starting the mower to see if the blade is moving.
  • Hydro-Lock. Check if the blade if clear and in good condition, and check the oil filter. If the filter is full of oil, the piston cylinder may be full of oil, which is causing hydro-lock. To drain the oil, remove the spark plug and crank the engine. The excess oil will spray out of the spark plug hole. Clean off any excess oil on the mower.

If your issue was not resolved, you probably have some other serious problem that may require you to take to the local repair shop.

Preparing Lawn Mower for Storage

Now that the mowing season is over, it’s now time to get your mower ready for storage during the winter. By doing this, the mower should start up easily in the spring.

  1. If you own a battery-powered mower. Remove the battery and store it in a cool dry place. Periodically, check to determine if the battery is fully charged. If not, charge it and make sure it’s fully charged when spring comes around. After removing the battery, wipe it off with a clean cloth. Clean the battery terminals using a metal brush or a terminal cleaning product. Coat the terminals with a terminal protector. Follow steps 3 and 4 below.
  2. If you own an electric mower. Check the electrical cord for any damage or cracks. If you should see any, replace the cord with a new one. Tighten up any loose screws or bolts. Be sure to follow steps 3 & 4 below.
  3. Clean the Mower. Before starting, remove the spark plug lead wire so the engine won’t start. On all types of mowers, be sure to clean, brush off leaves, dirt, and mud from the mower. Be sure under the deck is also clean and remove any debris.
  4. Check the Blade. Check the blade to determine if it needs to be sharpened or it is bent or chipped. Sharpen the blade according to the instructions in the owner’s manual. Replace the blade if it is chipped, warped or bent.
  5. Gas Storage. Be sure that you add a fuel stabilizer into the fuel to keep it fresh over the winter. Gas begins to degrade after 30 days and causes fuel system clogging. Fill the tank with a stabilizer added fuel and let the engine run for a couple of minutes to allow the mixture to circulate through the system. Also, a full tank of gas prevents any moisture build-up from condensing in the tank which can form rust that can break away and clog the carburetor. By adding a fuel stabilizer you don’t have to drain the fuel out of the gas tank when the mower goes into storage. It also ensures a quick easy start in the spring. Store mower in a safe dry area. If you have to store it outside, cover the mower with a secure tarp. Check throughout the winter that the tarp is not torn or have any openings.
  6. Check the Air Filter. This is an excellent time to check the air filter. If it’s dirty, clean it according to the instructions in the owner’s manual. Otherwise, replace it with a new one.
  7. Check the Fuel Filter. Check the fuel filter for any dirt or debris and clean it. The owner’s manual should mention how to clean the fuel filter. If it’s too dirty, replace it with a new one. Check the owner’s manual for the part.
  8. Check the Spark Plug. Now is a good time to check the spark plug. Remove it to see if it is dirty or has some carbon build-up on the tip. Clean the spark plug according to the instructions in the owner’s manual. If it is too dirty, replace it with a new one.
  9. Self-Propelled Mowers. Be sure to check all the belts that they have no wear or are damaged. If you should notice any damage, replace the belt with a new one. The owner’s manual should tell you the part to get. If not, you can call the manufacture for that information.
  10. Check the Oil. Now is a good time to check the oil to see if its dirty. The oil should be changed after 50 hours of operation and 100 hours for riding mowers. It’s a good idea to change the oil at the end of the mowing season. Check the owner’s manual for the correct type of oil.

After you have done the above, your mower is now ready for storage for the winter. When spring arrives, it should start up easily without any issues.


Lawn mowers at some time in the future will not work and fail to operate. We mentioned a few of the possible reasons why your mower could be experiencing a problem. We hope these solutions can help you revolve your mower problems yourself.

You then can take the appropriate action to try to fix the problem without having to go to the local repair shop. Most of these fixes are DYI (do it yourself) repairs.

However, some problems are beyond what we mentioned here and will need a pro to help you. You can call the manufacture to get their input for a possible solution if the owner’s manual did not cover your issue. Or, take the mower to the local repair shop and have them look it over to see if it’s repairable.

We also provided some valuable information on how to winterize your lawn mower so it’s ready in the spring.

If all else fails, the only solution is to purchase a new lawn mower.

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