Lawn Mower Carburetor Cleaning

Lawn Mower Starts Then Dies

This is part 2, if you missed part one check it out here, (internal link). Okay, I will assume you have tried cleaning the fuel bowl as per part one of the guide, without success. Now you need to remove the carburettor, clean it and replace carburettor gaskets if they tear when removing the carburettor.

 

There are many different styles of carburettor, 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.

 

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

 

Preparation

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 nuts and screws.

 

Gas burns the skin so I advise wearing surgical gloves and eye protectors. Gas stinks too, so make sure your in a well ventilated area.

 

If you find your carburettor is corroded, go ahead and replace it. You'll find a list of all the most common types on this page "New mower carburettors".

 

You might also find this page useful, "Carburettor repair tools", it lists tools I use to clean and repair or replace carburettors. The correct tools make the job easy.

 

 

Mower air filter

Remove

Remove plug wire and turn off fuel as before. Loosen bolt on the fuel bowl. Remove the air filter, clean or replace before refitting.

Mower air filter cover

Remove

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

Mower carburetor gasket

Photo

Pay attention to the gaskets and their locations. The gaskets are the paper type material sandwiched between the carburettor and engine. These gaskets must go in the correct location and orientation.

mower starter mower carburetor mower carburetor mower carburetor

Remove

Don't be intimidated by all the pipes and levers. It is straight forward. Take your time, lots of pictures and you'll be fine. 

A typical carburettor will have a fuel line, breather pipe, throttle lever and spring. May have a choke lever, depending on choke system.

It'll look like this, dirty, if you have compressed air, blowing off the grime makes seeing components easier.

Remove the gas line - use a screwdriver to prise it off.

Remove the crankcase breather pipe.

Remove the air filter housing bolts, and housing.

Holding the carburettor in one hand, turn it sideways to release the throttle link, spring and choke lever.

Mower carburetor Mower carburetor Mower carburetor

Strip

Move to a clean area, remove bowl.

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

The needle will have a rubber tip seal or the seal will be in the seat of the carburettor. 

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

Mower carburetor gasket Mower carburetor gasket Mower carburetor gasket

Jet

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.

The dirt collects in the jet because it has small port holes which gas flows through.

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

Mower carburetor gasket Mower carburetor gasket Mower carburetor gasket Mower carburetor gasket

Cleaner

Use carburettor cleaner to clean all the passage ways and port holes.

Spray through the fuel inlet pipe, throttle plate, choke plate, float and needle.

Drain the gas tank completely and change the fuel filter (if fitted). Some mowers have the filter in side the fuel line at the tank or in the tank.

Refit carburettor in reverse order.

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.

Fill mower with gas and turn on fuel.

Your ready to mow, Nice work!

Gas Flow Test

This section deals with a lack of gas flowing from the carburettor. The areas for consideration are: gas cap; gas tank; fuel lines; fuel filter; carburettor float needle seal. If your carburettor is supplying too much gas, then the float needle seal is worn.

 

Replacing the seal often won't work, and a better fix is to replace the whole carburettor.

 

Gas Cap

When gas caps get lost, improvising owners usually find something to fit the gas tank, I really like that style of problem solving. The thing is, a gas cap has a vent which allows the gas tank to breath.

 

A sealed tank will slow or stop fuel flow, causing the engine to lose power or stall. Drilling a hole in the improvised cap will fix the problem.

Gas Tank

Some lawn mower gas tanks have a filter in the bottom where the out let is. The filter can block as can the out let pipe, causing fuel starvation.

 

Cleaning the tank may require removing, turning upside down and blowing compressed air in through the out let pipe.

 

mower gas cap

Vented

A fuel tank needs to breath. When fuel leaves the tank it needs to be replaced with air. 

gas caps

Faulty

A sealed tank will prevent fuel from flowing.

To test cap, remove fuel bowl and then remove cap, if fuel flows now then gas cap is faulty.

mower gas tank mower gas tank

Inspect

Check the gas tank, look inside for debris blocking the outlet hole.

If you can't see in, remove the out let pipe and check flow, it should by a constant steady flow.

Dirt in the tank is very common and it will slow or block gas flow. Sometimes it may be necessary to remove the tank to clean.

Fuel Lines

Problems with fuel lines usually revolve around leaks, which are easy to identify. Other less common problems are: pinching of the line; blockage; breaking down of the inner wall of the fuel line itself.

 

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.

 

Ride-on mower starter

Flow

Check flow on lines.

mower starter

Leaks

Check walls for cracking and leaks.

Gas Filters

 

Not all mowers have a traditional style fuel filter, some don't have any. Filters can be found: in the fuel line; bottle type on the fuel line; mesh in the bottom of the gas tank;  filter in the filler neck.

 

Check which one you have and make sure it's clean.

 

Mower gas filter Mower gas filter Mower gas filter

Failure

Check the fuel filter, common types are:

Bottle type 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 a mesh screen in the bottom of the fuel tank. They can be cleaned and reused.

To test remove the fuel line at the carburettor, no flow suggests a filter/gas tank block.

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 carburettors aren't expensive or hard to fit, sometimes it's best to replace the whole carburettor. 

mower carburetor float mower carburetor float mower carburetor float

Failure

Remove the float by sliding the pin out. Check the needle seal.

The needle tip seal turns pink when worn, some carburettors will have the seal in the carburettor needle seat instead.

mower carburetor mower carburetor

Spray

Use fine wire to clean out the needle seat in the carburettor.

Blow some WD carb cleaner into the needle seat on the carburettor.

Fuel should start to flow, if it doesn't, remove and clean carburettor or replace with a new unit.

Related Questions

Related Questions

Where is the carburettor located on a lawn mower? The carburettor on a lawn mower is usually located towards the front of the engine opposite the muffler. The carburettor is positioned behind the air filter cover, the air filter is usually a black plastic square / rectangle cover.

 

Can you clean a carburettor with wd40? WD40 won't be very effective at cleaning a gummed carburettor. Carburettor cleaner is specially formulated to break down gumming deposits. 

Auto Technician and Writer at | Website

John Cunningham is an Automotive Technician and writer on Lawnmowerfixed.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write "How to" articles that help fellow gear-heads with all aspects of mechanical repairs, from lawn mowers to classic cars.