Lawn Mower Carburetor Cleaning - Beginners guide with pics

By: Author John Cunningham. Published: 2019/08/14 at 11:34 am

Okay, I will assume you have tried cleaning the fuel bowl as per part one of the guide without success. If you haven’t drained the bowl yet, check out this video – “Gas bowl draining” before moving on to carburetor cleaning.

When bowl draining doesn’t work, we’ll need to remove the carburetor, clean it, and replace carburetor gaskets if they tear when removing the carburetor.

There are many different styles of carburetor; yours may look different. Some will have a choke; others will have a priming bulb. Some will be more challenging to remove than others. All will need to be cleaned at some point.

This post covers the subject of cleaning your lawn mower carburetor pretty well, but if you need more help, check out “Carburetor cleaning video.” It covers removing, stripping, cleaning, reassembly, and refitting step by step.

If, while following the above guide, you find that you have no fuel flow, then proceed to the fuel flow check below.

Preparation & Tips

Before working on your mower, remove the plug wire and shut off the gas. Check out the mower repair safety video here.
It’s helpful to take pictures as you go; you’ll find them valuable when reassembling. Have a few rags handy and a container for fasteners. If you get stuck, check out these videos.
Gas burns the skin, so I advise wearing surgical gloves and eye protectors. Gas stinks, too, so make sure you are in a well-ventilated area.
If you find your carburetor is corroded, don’t waste your valuable time attempting to clean it. Go ahead and replace it. You’ll find a list of all the most common types on this page, “New mower carburetors”.

Tools You’ll Need To Clean Mower Carburetor

The correct tools for a task do two things: make you look like a pro and make the job move like butter. For carb cleaning, there are a few tools that make the job easier. You’ll find all the tools I use here on the “Carburetor cleaning tools” page and if you need video help on tool identification, check out the tools video here.

If you find your carburetor is badly gummed up or corroded, go ahead and replace it. A new carb only costs a few dollars; cleaning a badly stuffed carb isn’t worth your time. Check out the Amazon link below for common lawnmower carburetors delivered to your door.

Amazon Lawnmower Carburetors

Carburetor Removal

Remove – Remove plug wire and turn off the fuel as before. Loosen the bolt on the fuel bowl.

Remove – Remove the air filter, clean, or replace it before refitting.

Remove – Loosen the air filter housing, two or three bolts usually. Have a suitable container for small parts.

Photo – Pay attention to those gaskets and their locations. The gaskets are paper-type materials sandwiched between the carburetor and engine.

These gaskets must go in the correct location and orientation.

Remove – Don’t be intimidated by all the pipes and levers. It is straightforward. Take your time, lots of pictures, and you’ll be fine. A typical carburetor will have a fuel line, breather pipe, throttle lever, and spring.

It may have a choke lever, depending on the choke system. It’ll look like this, dirty if you have compressed air. Blowing off the grime makes seeing components easier.

Remove – Remove the air filter housing bolts and housing.

Remove the gas line – use a screwdriver to pry it off. Remove the crankcase breather pipe.

Turn 90° – Holding the carburetor in one hand, turn it sideways to release the throttle link, spring, choke, and lever. It’s now free and ready for the next stage, cleaning.

Stripping Mower Carburetor

Strip – Move to a clean area, and remove the bowl.

Remove – Remove the float and needle; this is done by pulling the pin.

Inspect – The needle may have a rubber tip seal, or the seal may be in the seat of the carburetor.

A worn seal turns pink. When seals wear, they can cause too much fuel flow or no flow at all.

Remove – Remove the main jet with a flat screwdriver. These jets are made from brass which is a soft metal and will damage easily. Be sure the screwdriver is a good fit.

Remove – Air fuel mix screw, but count the number of turns to remove the screw. You’ll need this info later when refitting the screw.

2 Types – Your jet may be one unit (integrated emulsion tube) or separate, meaning a jet and emulsion tube.

Cleaning Mower Carburetor

Cleaner – Use carburetor cleaner to clean all the passageways and portholes.

Spray – Thoroughly spray all ports – the fuel inlet port, float and needle ports, air /fuel port, throttle plate, choke plate, etc.

Clean – The dirt collects in the jet because it has small portholes which air passes through.

Make sure all these ports are clean. Use a strand of wire to push through the holes.

Spray – Use your carb cleaner.

Gas Bowl Bolt – Some carburetors (B&S) employ an integrated bowl bolt and jet; these guys are famous for blocking and causing no starts, rough running, etc.

If you have this type of bowl fastener, its ports must be clean. A strand of wire brush works great for cleaning.

Clean – Some carburetors may have an idle jet; use the fine wire to clean it also. Check out this guide for more detail on idle jet cleaning, it’s a generator, but the carburetor is identical.

Gas Tank – Drain the gas tank completely and change the fuel filter (if fitted).

Replace – Some mowers employ a gas filter inside the fuel line at the tank or inside the tank. Filters are covered in more detail below in the gas flow section.

Reassemble and Refit Mower Carburetor

Reassemble Carburetor – Remember to refit the air-fuel screw to the same number of turns.

Refit Carburetor – Remember to orientate those gaskets the correct way. Replace them if they’re damaged.

Fit the throttle, throttle spring, and choke controls before fitting the gas line. Don’t forget to fit the breather pipe to the rear of the air filter housing.

Gas Can – This bit gets overlooked, but it’s important. Clean out the fuel can. Check it for grit, and if you’re not sure the gas is good, replace it and use a gas stabilizer (see video here on gas stabilizer).

Fill the mower with gas and turn on the fuel. You’re ready to mow. Nice work!

Gas Flow Troubleshooting

This section deals with two common gas flow problems – a lack of gas flowing from the carburetor or too much gas flow. If you have either of these problems, you are in the right place.

The areas for consideration include:

Gas cap
Gas tank
Fuel lines
Fuel filter
Carburetor float needle seal

Lack of Gas Flow

If your carburetor isn’t supplying enough gas, it’s likely the problem rests with a lack of fuel caused by a gummed-up float needle port. The needle seal commonly degrades and blocks the port. Replacing the seal may fix the problem, but often, replacing the carb is a better fix. We’ll cover the testing flow and the repair below.

Too Much Gas Flow

If your carburetor is supplying too much gas, it’s likely the float needle seal is worn. Replacing the seal may not fix the issue; often, it’s better to replace the whole carburetor.

We’ll cover testing flow, common causes of gas flow issues, and the various repairs next.

Testing Gas Flow

Remove Bowl – Remove bowl to test flow

Gas Tap – Turn the tap on and off to control gas flow while testing

Gas Cap – When gas caps get lost, the MacGyver types usually find something to fit in its place. You know, old oil can cap or such.

The thing is, a gas cap has a vent that allows the gas tank to breathe.

A sealed tank will slow or stop fuel flow, causing the engine to lose power or stall.

This is an easy test: remove the gas cap and see if the engine starts and runs OK. A common symptom of a sealed gas tank is – the mower runs for ten minutes or so, then loses power and stops. If this sounds familiar to you, check that gas cap.

Gas Filter – Check the fuel filter; there are a few different types; the common types include:

Bottle types are easy to check, as most are see-through. They can’t be cleaned.
In-line filters are fitted inside the fuel line at the fuel tank. They can be cleaned and reused.
Tank filters are mesh screens at the bottom of the fuel tank. They can be cleaned and reused.

To test flow through the filter, remove the fuel line at the carburetor. No flow suggests a filter/gas tank block.

Remove the outlet pipe and check the flow; it should be a constant steady flow.

Mesh screen in base of the gas tank. Dirt in the tank is common and will slow or block gas flow. It may be necessary to remove the tank to clean.

Not all mowers have a traditional-style fuel filter; this is an inline filter.

Fuel Lines – Problems with fuel lines usually revolve around leaks, which are easy to identify.

Other less common problems include pinching of the line, blockage, and breaking down of the inner wall.

Some manufacturers say that the alcohol in the ethanol-blended fuels is damaging the rubber and plastic components of their engines. Manufacturers specify regular gas or e10.
They don’t recommend e15 and e85.

Check walls for cracking and leaks.

Needle Seal – Float needle seals, are made from rubber; they can be located on the tip of the needle or embedded in the needle seat. Either way, they wear over time and can break down, causing a blockage.

Seal kits are available, but whole carburetors aren’t expensive or hard to fit; sometimes, it’s best to replace the whole carburetor.

Failure – Remove the float by sliding the pinout. Check the needle seal.

The needle tip seal turns pink when worn; some carburetors will have the seal in the carburetor needle seat instead.