How to rebuild a lawnmower carburetor. With Helpful Tips

Lawnmowers require a maintenance check before every time they are about to be used. Staying on the shelf of your shed or backyard might have got the mechanisms a bit rusty. It is generally adequate to check the lubricant oil level, fuel supply, oil, and air filter and keep the machinery clean by wiping any dirt off.

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.

Sometimes cleaning the carburetor fixes the problems, but you might have to check the carburetor for leakages in the gaskets and seals. In the latter case, you will have to rebuild the carburetor.

How to rebuild a lawnmower carburetor

• Step 1: Remove the spark plug connector
• Step 2: Locate the Carburetor
• Step 3: Remove carburetor and disassemble it
• Step 4: Clean the carburetor
• Step 5: Disassemble the carburetor
• Step 6: Replace all the gaskets and washers from the rebuild kit
• Step 7: Assemble the carburetor and mount all removed accessories back as they were

Reasons to rebuild the carburetor

It is always better to know the reason behind every repair and how you can do the maintenance yourself. A better knowledge of the root cause and effects of malfunctioning any part of the machinery is useful. If reasons are known, a better common-sense approach can opt during the rebuild of the carburetor.

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.

• 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

Just knowing the reason is only half the knowledge a repairer should have. The effects caused by the above-mentioned is also essential.

Effects of a faulty carburetor system are

• 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 can not be corrected by tappet timing.

Replacing the carburetor might seem to be the only option, but with proper reasoning, it can be made conclusive that rebuild is a far better option in many cases. Rebuilding does not require a lot of mechanical expertise and is a relatively easy repair process.

Step by step guide to Carburetor Rebuild

Elaborating further on the introduction steps, these significant steps can be further divided into sub-steps.

Before getting into more nitty-gritty of the rebuild procedure, it is useful to get familiar with all the required equipment.

1. Rebuild carburetor kit
2. Wrench set
3. Screwdriver
4. Safety goggles
5. Gloves
6. Carburetor cleaner
7. Water
8. Towels

The explanation and instruction on how to carry out each step during the carburetor rebuild are discussed below.

Step 1: Remove the spark plug connector

Spark plugs are present in gasoline engines. Their primary purpose is to produce a spark for the combustion of fuel.

• Remove the outer casing of the mower. The cover is usually screwed to the base and rarely clipped on.
• Locate the wire that is attached on the top of the engine
• Pull the connector to remove the wire

Step 2: Locate the Carburetor

It is generally present on the side of the engine block. Adjacent to the fuel tank and pipe connects both. Over carburetor and air filter compartment is also present.

An additional step after locating all of the components is to remove the air filter.

• Release the catch of the air filter cover
• Pull the cover off
• Remove the breather pipe that is usually present on the air filter side connected using spring clamps.
• Unscrew the filter at the base and pull it out to remove it.

Step 3: Remove carburetor and disassemble it

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 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 4: Clean the carburetor

Use a cloth and all-purpose cleaner to wipe any remnants present on our surface. Using a screwdriver, open up the carburetor and use a small gauge wire of platinum to remove dirt clogging any holes in the fuel supply. Along with disassembly, that will be explained in the next step, keep following these cleaning procedures. 

Step 5: Disassemble the carburetor

To disassemble 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 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 6: 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. 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.
• Step 7. 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 outer cover of carburetor, replace the choke return spring.

Step 7: 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.

• 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.
• Ensure the bowl gasket is adequately arranged and reposition the bowl if necessary.
• Move the restored carburetor smoothly back onto the mounting bolts and fasten the throttle coupling to the throttle lever.
• Reattach the fuel line to the carburetor and fuel tank.
• Relocate the air filter casing together with the air filter and filter cover.
• Reinstall the engine cover, blower cover, and starter rope

Associated Problems

• Stuck screws, plugs, or gaskets: Use a lubricant spray or a surface cleaner and try applying more force or use a wrench where possible instead of a screwdriver.
• Plastic clamps or clips broken due to equipment age: Using adhesive for repairing them or binding wire or steel clips can be used by making holes on both sides and clamping the components together.
• Extra Gaskets in a rebuild: Generally, no different gaskets are present. Use the manual or detailed diagram to locate the actual place of the extra gasket. As some of the gaskets completely diminish as they blow due to heat.

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.

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. How to clean a carburetor?

General steps are:

• Cleanup of the air filter
• Spray pressurized carburetor cleaner from the air intake side
• Wipe the dirt using a cloth
• Blow pressurized air from the drain plug side

3. 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 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 realize how to rebuild your lawnmower carburetor, you can retain your Lawnmower longer. A better operating carburetor will ensure the right engine working conditions, extending the life span of machinery.