Many machine owners will encounter a common problem, which is that the lawn mower sometimes cannot start, and most are caused by the lawn mower carburetor being blocked or corroded, because the carburetor is the connecting component between air and fuel, it converts the fuel in the lawn mower engine into the mechanical force needed to drive the engine. For machine owners, regularly cleaning and maintaining the lawn mower's carburetor is very important, it can solve various problems, especially problems that appear after winter or other long periods of non-use.
What Does a Lawn Mower Carburetor Do?
The purpose of a lawn mower carburetor is to mix the air and fuel in precise amounts to make the mixture ready for combustion. The carburetor then releases this mixture into the engine's cylinders where it is ignited by the spark plug, creating a controlled explosion that generates power to run the engine. Depending on the machine, the carburetor can adjust the air and fuel mixture to meet the needs of the lawn mower. This process, which we refer to as the AFR Calibration Cycle (Air-Fuel Ratio Calibration Cycle), is the foundation of efficient engine performance.
With all of the grass, twigs, and other debris that a small engine encounters, it's not surprising that even passages inside the carburetor eventually pay a price. Deposits inside the carburetor can clog fuel and air passages and reduce performance or stop the engine altogether.
Where Is a Lawn Mower Carburetor Located?
A lawn mower carburetor is a small, metal device that is typically shaped like a box or cylinder. This part of the mower can be found close to the air filter and the engine, secured with a few screws or bolts. Alternatively, you can track down the location of the carburetor by tracing the fuel line from the gas tank to the engine. The carburetor is located where the fuel line connects to the engine. If you are still in doubt, check the owner's manual for the lawn mower to get a definitive answer on where the lawn mower carburetor is located on your specific machine.
On most push mowers, the carburetor is located on the side of the engine, near the air filter and attached to the fuel line and throttle cable. For riding mowers, it's typically under the air intake cover, mounted to the engine block.
Signs Your Lawn Mower Carburetor Needs Cleaning
If you're experiencing the following symptoms, a dirty carburetor may be to blame. Through years of hands-on repair work, we've developed what we call the 5-Point Carburetor Diagnostic Protocol to quickly identify carburetor-related issues:
- Difficulty Starting: If your mower takes multiple pulls to start or refuses to start at all, the carburetor may be clogged, restricting fuel flow to the engine.
- Stalling or Rough Running: A mower that starts but sputters, stalls, or runs inconsistently often has a carburetor that isn't delivering the right amount of fuel.
- Black Smoke from the Exhaust: This could mean the carburetor is delivering too much fuel. A clogged air filter is often a contributing factor.
- Increased Fuel Consumption: If your mower burns fuel more quickly than normal, the carburetor may be supplying too much gas due to a disrupted air-fuel balance.
- Unstable Throttle Performance: If the engine revs unpredictably or bogs down under load, inconsistent fuel mixing due to a dirty carburetor may be the cause.
- Visible Build-Up on the Carburetor: If you notice dirt, varnish, or grime on the carburetor's exterior, there's a good chance internal blockages are also present.
While the carburetor is a common culprit for engine performance problems, it's not the only component that can cause similar issues. A weak spark plug can make starting difficult, a clogged air filter can lead to rough running, and a faulty governor can cause erratic throttle performance. Before assuming the carburetor is the problem, it's worth checking these parts as well.
Tools and Materials Needed
Before you begin cleaning the carburetor on your lawn mower, gather all the necessary tools and materials:
- Screwdriver (Phillips and/or flathead)
- Socket wrench set or nut driver
- Needle-nose pliers
- Carburetor cleaner spray
- Compressed air
- Clean cloths or rags
- Small cleaning brush (soft-bristled)
- Small wire or bread tie wire (for clearing jets)
- Container or bucket (to catch fuel)
- Nitrile gloves
- Safety glasses
Before You Begin
It's important to begin the lawn mower carburetor cleaning process by cleaning the outside of the engine while it is turned off. This makes it easier to keep the internal parts of the carburetor clean during disassembly. Also, it's necessary to take the time to clean your work area, which should be well lit to avoid losing any small parts while you work.
Have a clear space on your workbench where you can disassemble, clean, and reassemble the various parts of the carburetor. Additionally, it's a good idea to remove the spark plug cable by simply gripping the black plug and pulling directly away from the engine. This prevents the risk of the engine suddenly starting while you work.
Safety Note: Turn off your mower and give it time to cool down. If you've used it recently, the inside of your lawn mower could be extremely hot to the touch. Work in a well-ventilated area since cleaning involves chemicals. Wear protective gloves and safety glasses at all times.
Two Methods for Cleaning a Carburetor
You have two options for cleaning a carburetor: keeping it on the mower or taking it off. Typically, whether you leave the carburetor on or remove it for cleaning depends on how dirty it is. Based on our field experience, we've developed the Tiered Maintenance Approach—if the lawn mower has been running well and you make consistent efforts to keep up with lawn mower maintenance, it likely needs a thorough cleaning of the removed carburetor only once a year or after extended time not in use.
Method 1: Cleaning the Carburetor Without Removing It (Surface-Level Flush)
This method is best for routine maintenance or addressing minor clogs. We call this the Surface-Level Flush Technique—take these steps a few times each year to clean a lawn mower carburetor without removing it from the lawn mower:
- Turn off the lawn mower and give the engine enough time to cool down before starting the cleaning process.
- Disconnect the spark plug cable by grabbing the plug and pulling away from the engine. This will prevent the engine from starting while you work.
- Remove the air filter housing after a quick inspection to determine if it's attached with clips or screws. Remove and clean the air filter. Replace it if it is damaged or excessively dirty.
- Use an air compressor or brush to remove clippings, dirt, and gunk from the outside of the carburetor and linkage.
- Check the throttle and choke linkages. The connections attached to the carburetor's throttle and choke plates can bind or stick when dirty. Manually move them back and forth while spraying carburetor cleaner to work the cleaner into any stubborn spots.
- Spray carburetor cleaner into the carburetor throat and jets. Read and follow the directions provided by the manufacturer to determine how much carburetor cleaner to use.
- Blow out any remaining debris with compressed air to get rid of stubborn particles that might be clinging to the corners and crevices of the carburetor.
- Reconnect the spark plug wire, start the motor, and spray carburetor cleaner into and around the center of the carburetor. Let the mower run for a minute or two.
- Reattach the air filter and outer casing.
Method 2: Removing and Thoroughly Cleaning the Carburetor (Deep-Clean Protocol)
Although removing the carburetor makes it easier to thoroughly clean each part of this important lawn mower component, it also takes more time and effort. This method, which we call the Deep-Clean Protocol, is recommended once a year, especially before the first use after winter storage.
Step 1: Remove the Carburetor
- Take a photo for reference—it will come in handy when it's time to put everything back together. Note the location of any cables or hoses so you can put them back in the proper place.
- Disconnect or remove the spark plug.
- Remove the cover and air filter.
- Disconnect the throttle and choke linkage cables from the carburetor.
- Prepare a bucket or container to catch the fuel before removing the fuel lines from the nipples of the carburetor housing with needle-nose pliers. Have a rag handy to clean up any fuel that spills.
- If no gas comes out of the fuel line, you might have a plugged fuel line or fuel filter, which will have to be addressed before reassembling the lawn mower.
- Once you've disconnected the fuel line, clamp it to prevent further leaking.
- Use a nut driver or socket set to remove the two bolts that hold the carburetor to the engine.
- Pull the carburetor off the mounting studs, taking care to avoid damage to the main gasket between the carburetor and the engine. Make a note of the position of the carburetor so that you don't reinstall it upside down.
Step 2: Disassemble the Carburetor
A key reminder before disassembling your carburetor is that every piece you remove needs to be put back in the same position. Consider taking pictures while you work to help prevent confusion during reassembly. We call this the Photo-Reference Method—a simple but essential habit that prevents reassembly errors.
- With the carburetor in the middle of your clean work area, start the disassembly process by cleaning around the bowl with carburetor cleaner.
- Unbolt the fuel bowl (usually located at the bottom) and ensure the hole in the nut is clear of any obstructions by poking a paper clip or piece of thin wire through it.
- Remove the float, which should be attached to the carburetor with a hinge pin.
- Also remove and inspect the needle. Replace if necessary. Keep all of the parts grouped together.
Step 3: Clean the Carburetor Parts
This is where the Passage-by-Passage Clearing Technique becomes critical—systematically working through each jet and passage ensures no blockage is missed:
- Spray carburetor cleaner directly into the carburetor jets and passages, allowing the cleaner to soak for several minutes.
- Use a soft-bristled brush to remove any stubborn debris.
- Take particular care to clean the needle and needle seat, through which the carb draws fuel into the float bowl.
- Use a small soft wire, like one from a bread tie, to ensure the passages are clear. Pay close attention to the small hole in the threaded area of the bowl nut—this is the high-speed jet and is often plugged.
- Spray carburetor cleaner up the center nozzle of the carburetor until it shoots out the throat of the carb.
- If you prefer to use a liquid carburetor cleaner over a spray cleaner, pour the cleaner into an empty bucket. Wire the larger parts of the carburetor together, then carefully lower them into the bucket filled with carb cleaner. Soak all parts for about an hour.
- Important: Be aware that the solvents in these cleaners can dissolve rubber and many plastics. Avoid getting carburetor cleaner on non-metallic parts, as it can cause them to decompose and further clog the carburetor.
Step 4: Replace Worn Parts
Even the best carburetor cleaning cannot repair worn-out parts. Should you spot significant wear and tear on carburetor parts, including the float, pin, needle, or gaskets, then get a carburetor repair kit for your specific carburetor to make necessary repairs. Some carburetor parts, like gaskets, wear out more quickly than other parts. While your carburetor is disassembled, take the opportunity to replace its gaskets—this is an inexpensive and easy way to save you from future headaches.
Step 5: Reassemble and Reinstall
- Rinse the carburetor parts with water to remove excess carburetor cleaner. Then, blow-dry the parts with compressed air or let them air dry. It's essential that the parts are completely dry before reassembly.
- Begin putting the carburetor back together. Use any pictures you took during disassembly to ensure that you are correctly reassembling the parts.
- Mount the carburetor back on the lawn mower.
- Reattach the throttle and choke linkage cables.
- Reinstall the fuel lines and spark plug cable.
- Fasten the bolts on the carburetor and reattach the air filter to the mower.
- Add fresh fuel to the tank.
Testing After Cleaning
After you have reassembled and reinstalled the carburetor and air filter, add fuel to the gas tank and start the lawn mower to ensure that the maintenance was a success. We recommend a Three-Stage Verification Test—check to see that:
- The engine runs smoothly and efficiently without stuttering, overheating, or smoking.
- Any issues with starting or running have stopped. If they persist, a dirty carburetor likely is not the reason for the problems.
- The engine runs smoothly at various throttle settings.
- Rough running is normal at first, as cleaner residue burns off. Let the engine warm up for 2-3 minutes.
If the engine refuses to start after several tries, the problem might be more serious. In that case, take your mower to a small engine repair shop.
How Often Should You Clean Your Carburetor?
The carburetor is a key component for the smooth operation of the machine, so it's necessary to be diligent about cleaning a lawn mower carburetor. Generally, the lawn mower carburetor should be cleaned between two and three times a year, although this varies with frequency of use.
It's wise to remove the carburetor for a thorough cleaning once a year. The best time to conduct this thorough cleaning is before the lawn mower is used, right after the winter ends. This will help ensure the lawn mower is in good condition before attempting to start it up after months of sitting idle. Clean the carburetor without removing it an additional one or two times a year, depending on usage and condition.
How to Prevent Carburetor Buildup
Making sure fuel is fresh when you fill the tank is a simple way to avoid a dirty carburetor. We've found that following what we call the Fuel Freshness Rule—using fuel no older than three weeks unless mixed with a quality stabilizer—dramatically reduces carburetor issues. Here are some tips to prevent carburetor problems:
- Use Fresh Fuel and a Stabilizer: Old fuel breaks down and leaves deposits that clog the carburetor. Always use fresh fuel and add a stabilizer if the mower will sit unused for extended periods. Today's fuels containing MTBE and ethanol are not as stable as those from years ago.
- Check and Replace the Air Filter: A dirty air filter allows contaminants into the carburetor. Regularly inspecting and replacing the filter prevents buildup and ensures proper airflow.
- Run the Mower Dry Before Storage: Running the engine until it burns off the remaining fuel prevents residue from forming in the carburetor, reducing the risk of clogs when restarting in the next season.
- Empty the Tank or Add Fuel Stabilizer Before Winter Storage: Before storing the mower at the end of the season, always empty the tank or add a fuel stabilizer to keep the gas from degrading.
- Perform Annual Maintenance: As part of your annual lawn mower maintenance, you should always replace the air filter and fuel filter with new ones, check the spark plug, and change the oil.
Conclusion
Cleaning your lawn mower's carburetor is an essential maintenance task that ensures the engine runs smoothly and efficiently. When the carburetor is clogged or dirty, it can cause the engine to run poorly or not start at all. Regular cleaning can prevent these issues, ensuring that your lawn mower operates smoothly every time you use it.
While professional carburetor cleaning can cost $36-50 per visit, once you know how to handle this maintenance yourself, it can be done for under $15 and about 30 minutes of work. Whether you remove the part or leave it inside the machine, cleaning a lawn mower carburetor can keep your machine running smoothly for years to come.
If you're in the market for a new lawn mower, consider models that are designed for easy maintenance access. Taking the time to clean and maintain your lawn mower's carburetor ultimately saves you money and hassle in the long run.