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How to fix a lawnmower carburetor

You have your lawnmower for quite a while now. Your property has been looking fresh and beautiful. One fine morning, you decide to spend some time maintaining and fixing some issues with your lawnmower. You check the oil level, clean the outer cover and fuel level in the tank. You give a pull to the starter rope to give your machine a check run. At this moment, you realize some irregularity in the behavior of the engine.

How to fix a lawnmower carburetor:

  • Step 1: Remove the outer casing of the engine.
  • Step 2: Remove the spark plug connector
  • Step 3: Check Air Filters and its housing and clean the air filter
  • Step 4: Locate the Carburetor
  • Step 5: Remove carburetor and disassemble it
  • Step 6: Clean the carburetor
  • Step 7: Disassemble the carburetor
  • Step 8: clean all openings and jets using a cleaner
  • Step 9: Replace all the gaskets and washers from the rebuild kit
  • Step 10: Assemble the carburetor and mount all removed accessories back as they were
  • Step 11: Install the carburetor back with new main gaskets around the air filter connection and backplate

A carburetor is an essential component of a Lawnmower. Without a properly functioning carburetor, fuel supply is interrupted and can result in many issues. Like the engine of a Lawnmower might stall, run rough, or might not even start altogether.

You deduce that the carburetor might be faulty, and it is time to fix the issue. There are two approaches to tackle this problem.

The choice between these methods is made based on the health of gaskets in general. Gaskets are the seals that are present around all significant contact points between components of the carburetor.

A combination of both cleaning and rebuilding is the best way of fixing the issue


Causes of a faulty carburetor

Before fixing the carburetor, it is essential to know what are the causes. Understanding the grounds of a faulty carburetor will enable you to take better care and measures to extend and improve a lawnmower’s life.

  • Rusty interior: As the fuel stays inside the carburetor, it reacts with metallic parts and corrodes them. All plastic parts also are prone to damage.
  • Excessive heat: From the engine compartment, a lot of heat flows to the carburetor as well. This heat causes damage to the gaskets present.
  • Bad Fuel Quality: Using a lower grade of fuel causes damage to the carburetor and the engine.

Effects of a lousy carburetor

Knowing all the reasons that result in a faulty carburetor, it is vital to gain knowledge on the effects. It will enable you to have better insight. You will be able to see the symptoms better and earlier, saving a lot of time and money on the extended repair.

  • Due to weakened and old gaskets, leakage of pressure persists. Air good air to fuel ratio is difficult to maintain.
  • Old spring and needle valve resulting in inadequate intake for combustion and low economy
  • Slow start of the lawnmower. A lot of force is required to pull the starter rope.
  • The rough running engine of the mower. Producing a lot of whirring noise
  • Bad fuel economy. The fuel intake ratio is disturbed and cannot be corrected by tappet timing.

But there is nothing to worry about as fixing a faulty carburetor is a lot easier, and you may not require any professional help at all. Carrying the procedure out on your own saves you a lot of time and money and imparts you with your machinery’s better technical know-how.

A carburetor is the part of a Lawnmower that mixes fuel and air and feeds it to the engine block for combustion. The combustion of this air-fuel mixture then results in power generation. The power is transferred from the piston to the crankshaft. The carburetor is usually situated along the side of the engine below the top cover of the lawnmower. After aging the system and spending many usage cycles, carburetor gaskets and washers became weary and old.

A step by step guide to fix a lawnmower carburetor

● Step 1: Remove the outer casing of the engine.

  • Step 1: The cover is usually screwed to the base and rarely clipped on.
  • Step 2: After unscrewing the casing, lift it off the engine.
  • Step 3: Give the engine cleaning with an old shop rag.

● Step 2: Remove the spark plug connector

  • Step 1: Locate the wire that is attached to the top of the engine
  • Step 2: Pull the connector to remove the wire
  • Step 3: Use a plug gripper to ensure the safety of the insulation on the wire
  • Step 4: Clean the inner side of the terminal

● Step 3: Check Air Filters and its housing and clean the air filter

  • Step 1. Remove the air filter screws: Remove the screw holding on the air filter
  • Step 2. Remove the carburetor screws: Remove the screws holding on the carburetor
  • Step 3. Remove the housing: pull the housing off; by doing this, the carburetor becomes visible.
  • Step 4. Remove the breather pipe: Remove the breather pipe that is usually present on the air filter side connected using spring clamps.

For cleaning the carburetor, the principal thing is to make sure that the air filter is free of twigs, dirty grass, and debris. A clogged or blocked air filter will create black smoke that can be seen coming out of the muffler. It will block the air passage for our carburetor, and thus it cannot “breathe” due to hindrance. Wash the filter if possible, and let it dry.

● Step 4: Locate the Carburetor

Just behind the air filter, there is a boxy compartment. A fuel pipe also extends through its side. This part is the carburetor.

● Step 5: Remove the carburetor from the main body of the lawnmower

Removing the carburetor is the core step in this procedure and consists of various sub-steps and additional related components and pipe removal.

  • Step 1: Empty the fuel tank in a safe container. First, loosen the spring clamp of the fuel pipe from the tank side. Place the container underneath to collect the draining fuel.
  • Step 2: Releasing the starter rope. It is done to decrease the pulling tension and eject any stuck fuel back to the connection line.
  • Step 3: Unscrew the blower casing. Now pull the cover off to remove it. Be gentle while pulling to make sure not to break the shell or damage the fastening points.
  • Step 4: Separate the carburetor mounting brackets to release the carburetor. Mounting brackets are commonly present on sides in the shape of arms.
  • Step 5: Disconnect the carburetor from the carburetor adapter. The adapter is an electronic connection of the carburetor present on the backside.
  • Step 6: For disconnecting the governor and choke linkage, hold the carburetor above the bracket.
  • Step 7: Release the fuel line spring clamp and pull the fuel line off the carburetor.

Now smoothly apply force and pull the carburetor out. Take the carburetor to the working desk with sufficient lighting and a clean surface. 

● Step 6: Clean the carburetor

Using an all-purpose cleaner and a wire brush, remove all filthiness of the carburetor’s outer surface.

● Step 7: Disassemble the carburetor

While disassembling the carburetor, it is essential to know all the parts of it and its location. Here is a list of all components

  • Choke spring: Present on the top side of the carburetor and hooked on one side to a lever like protrusion
  • Float bowl: present inside the lower cover of carburetor. It is a hollow cavity with a float current inside it.
  • Drain plug: present on the lower side of the carburetor outside the cover. It holds the fuel inside for maintaining a constant supply.
  • Float bowl pin: a pivot pin for holding the float in place present in the float bowl 
  • Float valve
  • Needle valve: valve controlling fuel jet
  • Main Jet: the common link between float and needle valve  
  • Outlet port: port that gives fuel-air mix to the intake manifold of the engine

Identifying these components and unscrewing them will complete the disassembly procedure.

● Step 8: clean all openings and jets using a cleaner

There are two popular ways of doing this, either using a cleaner spray or using an ultrasonic machine.

– Using the spray cleaner

  • Spray the cleaner in the float bowl
  • Through all the fuel jets
  • Clean the carburetor body by inserting the nozzle through it and spraying
  • Clean the main jet and emulsion tubes similarly

– Using ultrasonic machine

  • Pour in water and set the machine
  • Put all disassembled parts inside
  • Run the machine
  • All dirt stacks will break down and flow into the water
  • Let the components dry and blow pressurized air through all openings

● Step 9: Replace all the gaskets and washers from the rebuild kit

Rebuilding the carburetor means changing the gaskets and seals, replacing the malfunctioning springs, and cleaning all components.

For rebuilding the carburetor, the rebuild kit should be bought from a hardware store. The match of the rebuild kit should be perfect based on engine make and model.

– Change the float drain plug gasket:

By using an Allen key, untighten the float drain plug. Make sure to put the safe fuel container below the drain. So, the fuel can flow into the box instead of getting spilled on the worktable. Remove the rubbery gasket present around the drain opening and replace it with a new one from the rebuild kit. After replacing it, lubricate around with petroleum jelly.

– Replace the central gasket, retainer, and O-ring:

  • Step 1. Open up the body of the carburetor using a socket screwdriver. Remove screws from the float bowl, revealing the inside of the carburetor.
  • Step 2. Remove the float bowl pin and take the float out. Now, the main jet will be visible. Remove the main jet as well.
  • Step 3. Retainer and O-ring: Below this, embedded in the top, will be the retainer and O-ring. Pull them out using grip pliers.
  • Step 4. Remove the needle and float valve as well, which are situated right next to the opening containing the retainer. After cleaning the inside, replace the O-ring and retainer with the new present in the rebuild packet. One O-ring is also present on the main jet nozzle, which is smaller in size.
  • Step 5. The central gasket present over the top of the main jet is also replaced.
  • Step 6. Lubricate with petroleum Jelly.

– Clean all components, openings, and holes:

When all components are removed, clean the carburetor using:

  • Cleaner spray
  • Compressed air
  • Small gauge wire
  • Brush
  • Wipe cloth

– Insert the new needle and float valves:

When all components have been cleaned, and the retainer and O-ring have been replaced. Install the new valves instead of the old ones, which were removed prior while disassembling.

– Change the float bowl gasket:

When reinstalling the float and pin. Change the larger gasket present around the float bowl

– Install new choke return spring:

After all of the above steps are followed, on the top of the carburetor’s outer cover, replace the choke return spring.

● Step 10: Assemble the carburetor and mount all removed accessories back as they were

Now all of the gaskets have been replaced. Assembling of the carburetor and all other removed components is performed in the following steps.

  • Step 1. Reassemble the carburetor: Initially, allow the carburetor to dry and then reassemble it, ensuring that you properly position the diaphragms, gaskets, metering plate, and primer base as required along with the float needle and float.
  • Step 2. Arrange the bowl gasket: Ensure the bowl gasket is adequately arranged and reposition the bowl if necessary.
  • Step 3. Mounting bolts: Move the restored carburetor smoothly back onto the mounting bolts and fasten the throttle coupling to the throttle lever.
  • Step 4. Fuel line: Reattach the fuel line to the carburetor and fuel tank.
  • Step 5. Air filter: Relocate the air filter casing together with the air filter and filter cover.
  • Step 6. Engine cover: Reinstall the engine cover, blower cover, and starter rope

● Step 11: Install the carburetor back with new main gaskets around the air filter connection and backplate

While installing the carburetor back, make sure to replace the main gaskets. These are elliptical.

  • Step 1. Remove older gaskets: Remove the remains of older gaskets using a razor blade
  • Step 2. Install new Gasket: Install the new gaskets by placing them in the long bolts that hold the carburetor in place

Precautionary Measures

  • Personal safety is paramount. Use gloves, safety goggles, and an apron to protect your clothing
  • Let the engine cool down. 
  • Choose a well-ventilated workspace. Suffocation and less air passage in injurious because of fuel fumes and other dirt particles.
  • Use a safe fuel container for draining the fuel. This container is helpful for the safety of surroundings and cleanliness and saves fuel for later use.

How to adjust a lawn mower carburetor

There are a few simple steps you can take to adjust your lawn mower carburetor. Most lawnmower carburetors will have two adjustment screws to adjust the fuel-air mixture for idle and high speed.

Follow these instructions to make your lawnmower run smoother and quieter.

● Adjust the carburetor Idle mixture

– Step 1: Remove the air filter

Find the air filter and remove it from the lawnmower. Ensure that the engine has cooled down. If you notice that the air filter is dirty, clean it. When damaged I recommend replacing it.

– Step 2: Adjust the idle adjustment screw

Locate the idle adjustment screw. It is generally the one closest to the air intake. First, turn the screw clockwise until it barely touches the seat. Followed by turning it counterclockwise for 1 1/2 turns. If you notice later it does not ideal well, you can adjust it a little bit

Another method is to start the engine. If you adjust the idle screw, you will notice the idle speed changing. Turn it such that it idles well.

– Step 3: Reattach the air filter

Put the air filter back, and check if the engine is idling fine.

● Adjust the carburetor high-speed mixture

– Step 1: Remove the air filter

Find the air filter and remove it from the lawnmower. Be careful when the engine is still hot. If you notice that the air filter is dirty, clean it. When damaged I recommend replacing it.

– Step 2: Adjust the high-speed adjustment screw

Locate the high-speed adjustment screw. It is generally opposite the idle adjustment screw, but bear in mind that not all lawnmower carburetors have one.

Now turn on the engine, and let it slightly warm up. Now put the lawnmower throttle in the regular mowing position. Adjust the high-speed adjustment screw clockwise and counterclockwise, to find the position where the engine runs fine.

– Step 3: Reattach the air filter

Put the air filter back, and check if the engine is running fine when throttling.

Related Questions

1. What if the engine still does not work at its best?

There is still nothing to worry about. Try improving the grade of fuel you are using. Add stabilizers, as suggested by the manufacturers.

2. Is WD-40 a good carburetor cleaner?

WD-40 is a very effective cleaner due to its dual cleaning action. First, its influential solvent explodes the hard deposits, and secondly, its decisive cleaning action leaves no debris and sludge behind. Its popularity has grown significantly over the years. But due to its inflammable nature must be handled with care.

Final Remarks

One of the most critical components for the functionality of a Lawnmower is the carburetor. It decides whether our lawnmower will provide service for years or fizzles early. When you learn how to fix your lawn mower carburetor, you can retain your lawnmower longer. A better operating carburetor will ensure the right engine working conditions, extending the life span of machinery.