Your Problem Will Likely Be Loose Battery Connections, Flat/Faulty Battery Or Faulty Starter Solenoid.

Your lucky, there can be lots of reasons a lawn mower won't start, but your mower is telling you clearly what the problem is.

The Lawn mower starts then dies? The most common reason a lawn mower starts and then dies, is because the carburetor is dirty.

Other possible causes include:

  • Stale/Dirty Gas
  • Faulty Choke
  • Gas Filter Blocked
  • Gas Tank Blocked
  • Gas Line Blocked

Cleaning the carb will fix the problem, and you'll need to drain the gas tank, it's all covered in this guide, so strap yourself in.

 

Image

 

The symptoms vary, you may have been directed here by one of the following problems: mower runs rough; runs but only with choke; splutters when I cut on a slope; dies when cutting grass; lawn mower starts and then dies; engine surging.

 

All of these conditions are consistent with a gummed/contaminated carburetor and or bad gas. 

 

 

Won't Stay Running

The reason it starts and dies - the engine gets gas from the choke operation (or primer bulb) - that gets it running, but the blockage in the carburetor starves it of additional gas and then the engine stalls.

 

Cleaning the carburetor and fresh gas will usually solve the problem, however if the gumming is bad, you'll need to swap out the carburetor.

 

 

mower carburetor gumming

Gumming

This carburetor is too bad to clean. 

Replace

Replacing is easy and the right repair for a badly gummed carburetor.


mower carburetor

Gumming


mower carburetor

This carburetor is too bad to clean. 

Replace


mower carburetor

Replacing is easy and the right repair for a badly gummed carburetor.

What's Gumming?

Modern fuels are mixed with alcohol, which is ethanol. The ethanol attracts small amounts of moisture from the atmosphere, this isn't a problem when the mower is being used regularly.

 

Unsurprisingly the complaint is most common in the spring, when over the winter months the gas has evaporated and left a gummy type deposit. The sticky gunk blocks up the tiny ports and passages of the finely balance carburetor. 

 

 

Gas Stabilizer

You can prevent this problem by using a gas stabilizer, I use a product called Sta-bil Storage, check the price here on Amazon. It's a lot cheaper than a new carburetor.  Mixed with the gas it will stop gumming and keep the gas fresh for up to 2 years.

 

The process is simple, dump the bottle of stabilizer into a full gas tank and run the engine a while to get the treated gas throughout the fuel system. You don't need to use it all season, just use it towards the end of the season, put it top of your winterizing checklist, so next spring it's pull and mow.

 

Check out my "how to winterize your mower guide", I cover everything you need to know.

 

The gas stabilizer won't clean your carburetor, to do that job we need carburetor cleaner.

 

 

Sludge


Mower carburetor

This carburetor is repairable, gumming is a carburetor killer.

Mix


riding mower battery test

Using a stabilizer at the end of the season will save you time, stress and money.

Ride-on mower battery jumping

Sludge

This carburetor is repairable, gumming is a carburetor killer.

Stabilizer

Using a stabilizer at the end of the season will save you time, stress and money.


gas stabilizer

Carburetor

Carburetors are found on all small gas powered motors. The function of the carburetor is to mix air and gas together. Although lawn mower small engines are simple, the carburetors are quite precise bits of kit.

 

They're designed to mix the air and gas to a ratio of 14.7 parts air to 1 part fuel, commonly known as AFR (Air Fuel Ratio). This ratio offers optimum performance.

 

When this ratio is changed, the mower won't run right. A blockage in the fuel system or faulty carburetor can cause the engine to run lean (lack gas), and a faulty, worn out carburetor or blocked air filter, can cause an engine to run rich (too much gas).

 

Common issues with carburetors are: stale fuel; water in fuel tank; tank blocked; fuel cap faulty; fuel lines blocked; fuel filter blocked; carburetor float needle gummed up. 

 

Repairing is possible but can be hit and miss. On the upside carburetors are cheap and easy to fit.

 

Choke

A Choke is a metal flap that literaly chokes off air entering the carburetor. This creates a richer fuel condition which is just what a cold engine needs. The richer fuel mix helps counteract the dense oxygen rich cold air.

 

As the engine warms up, moving the choke lever to off, opens the flap again. However if the flap doesn't open, the engine will stall as it's now getting too much gas. You can check the choke operation by removing the air filter and moving the choke lever.

 

Your mower may have manual choke flap, auto choke flap or primer bulb.

 

 

 

 


mower throttle lever mower carburetor

Choke On

Choke set to full to start a cold engine. The flap should be closed.

Choke Off

As the engine warms a little, move the choke to the fast/run position. The choke should be off at this point.

Check that it's moving to the off position.


mower throttle lever mower carburetor
Ride-on solenoid

Primer

Your mower may not have a choke, it may instead have a priming bulb.  

It has the same end result as the choke plate - gives the engine extra gas for cold engine starts.

Choke On


Mower throttle lever Mower carburetor choke plate

Choke set to full to start a cold engine. The flap should be closed.

Choke Off


Mower throttle lever Mower carburetor choke plate

As the engine warms a little, move the choke to the fast/run position. The choke should be off at this point.

Check that it's moving to the off position.

Primer


Mower throttle lever

Your mower may not have a choke, it may instead have a priming bulb.  

It has the same end result as the choke plate - gives the engine extra gas for cold engine starts.

Carburetor Jet

Ports are tiny precision drilled holes in a brass tube known as a jet. The jet lives in the center of the carburetor, and as the engine inhales air, it also sucks gas up through the port holes in the jet. 

 

 

 

Jet


mower starter binding

The jet feeds a measured amount of gas to the engine.

If the port holes block, they restrict gas flow which causes a mower to stall, lack power or just not start.

Carburetor jet

Jet

The jet feeds a measured amount of gas to the engine.

If the port holes block, they restrict gas flow which causes a mower to stall, lack power or just not start.

Fuel Bowl

 

All carburetors will have a fuel bowl. The bowl is a reservoir of gas which stands ready to feed the engine as needed. The carburetor jet sucks the gas from the bowl, through the small port holes. 

 

You'll find your fuel bowl behind the air filter, it's a distinct bowl like shape, and you shouldn't need to remove any other parts to gain access. Check this out, I wrote a complete guide on  "Bowl cleaning".

 

Bowl Bolt


mower carburetor fuel bowl feed bolt

Not every fuel bowl will have the fuel feed bolt. It is a hollowed out bolt that has a fuel feed port hole that feeds gas to the jet. 

If your mower has one, it must be super clean.

Grit

Dirt in the bowl is common and cleaning it will often have you back mowing.

When replacing the bowl, don't over tighten and be careful not to pinch the bowl seal. 


Mower fuel bowl

Float & Needle

A carburetor fuel supply usually consists of a fuel bowl, float and needle. The float is as its name suggests; a float, attached to it is a needle, with a rubber tip.

 

The function of the float is to lift the needle as the fuel level rises in the fuel bowl. When the fuel bowl is full, the needle attached to the float will be pushed against the fuel feed port, sealing it.

 

A worn needle seal can cause either too much gas to flow or too little. I wrote this guide to help you check "Carburetor gas flow".

 

 

Grit


mower carburetor float and needle

Needle and float together control gas flow to the fuel bowl. Any supply problems here will cause poor engine performance. 

Needle

Needle and float together control gas flow to the fuel bowl.

Any supply problems here will cause poor engine performance. 


Ride-on valve lash

Fuel Bowl Feed Bolt

The bowl will collect dirt and moisture and will need to be cleaned. In some cases you may only need to clean the fuel bowl and fuel feed bolt. Not all mowers have the fuel feed bolt.

 

 

Grit


mower carburetor float and needle

Needle and float together control gas flow to the fuel bowl. Any supply problems here will cause poor engine performance. 

Feed Bolt

Not every fuel bowl will have the fuel feed bolt. It's a hollowed out bolt that has a fuel feed port hole, it feeds gas to the jet. 

If your mower has one, it must be very clean.


Mower fuel feed bolt

Cleaning the Bowl

The bowl collects dirt and moisture that sneaks past the gas filter, and often just cleaning the bowl will solve your problem. However if the grit has entered the jet you'll need to strip down the carburetor and clean it.

 

I use fast acting WD40 Carb cleaner, you can check the price here on Amazon. The WD is good stuff, it gets into all the tiny passage ways and breaks down the varnish deposits.

 

Check out below how to clean the fuel bowl. It's usually held on with one bolt and sometimes that bolt is an important part of the fuel feed system.

 

If your gas is older than three months, its stale, so cleaning the bowl won't make it go. You need to drain the tank, carburetor bowl and fill with fresh gas. If this works out for you great! If not, don't worry, I wrote a simple guide that will help you - "Carburetor cleaning".

 

 

Pull Wire

When working on your mower, remove the plug wire.

This prevents accidential starts.


Ride-on mower starter
mower gas off

Gas Off

Turn off the fuel tap (if fitted), if not use a grips to gently squeeze fuel line.

If your gas is old, drain the tank. Remove an easy to access gas line or drain out through gas bowl.

Remove

The fuel bowl lives behind the air filter. It will be fixed to the carburetor by one bolt, usually. 

Honda fit a handy drain bolt, which allows you drain the bowl without removing. Nice!


Mower fuel bowl Mower fuel bowl
mower gas bowl bolt mower gas bowl bolt

Clean

Some Briggs and Stratton carburetor bowls are held on by a hollow bolt, its other function is to feed fuel to the main jet.

These hollow fuel feed bolts are prone to clogging.

Not all mowers have this fuel feed bolt. If you have, be sure to clean it. I pluck a wire strand from a wire brush to clean the bolt fuel feed hole.

Spray

If you have some carb cleaner, spray some up the main fuel jet.


mower carburetor clean
mower gas float

Flow

Turn the fuel tap on. Now with the fuel bowl removed check fuel flow.  A good flow should be seen when the float is in the dropped position. 

No flow when the float is in the up position. 

Clean

Clean and refit the bowl, take care to seat it correctly.

The seal not seen in this picture will usually stay on the the carburetor, sometimes it will come off with the bowl.


Mower fuel bowl
mower gas tank

Fresh Gas

If your fuel is fresh turn it on, fit the plug wire and give it her a try.

If your mower still runs poorly - Clean carburetor.

Pull Wire


Mower plug wire

When working on your mower, remove the plug wire.

This prevents accidential starts.

Gas Off


mower gas tap

Turn off fuel tap (if fitted), if not use a grips to gently squeeze fuel line.

If your gas is old, drain the tank. Remove an easy to access gas line or drain out through gas bowl.

Remove Gas Bowl


Mower gas bowl Mower gas bowl

The fuel bowl lives behind the air filter. It will be fixed to the carburetor by one bolt, usually. 

Honda fit a handy drain bolt, which allows you drain the bowl without removing. Nice! 

Clean


mower gas bowl bolt mower gas bowl bolt

Some Briggs and Stratton carburetor  bowls are held on by a hollow bolt, its other function is to feed fuel to the main jet.

These hollow fuel feed bolts are prone to clogging.

Not all mowers have this fuel feed bolt. If you have, be sure to clean it. I pluck a wire strand from a wire brush to clean the bolt fuel feed hole.

Spray


mower carburetor cleaning

If you have some carb cleaner, spray some up the main fuel jet.

Flow


mower gas tap

Turn the fuel tap on. Now with the fuel bowl removed check fuel flow.  A good flow should be seen when the float is in the dropped position. 

No flow when the float is in the up position. 

Clean Bowl


Mower gas bowl

Clean and refit the bowl, take care to seat it correctly.

The seal not seen in this picture will usually stay on the the carburetor, sometimes it will come off with the bowl. 

Fresh Gas 


mower gas tank

If your fuel is fresh turn it on, fit the plug wire and give it her a try.

If your mower still runs poorly - Clean carburetor.

Tune-up

Your mower engine should be serviced at least once per season, ideally in the spring. Tune-up kit includes: oil; plug; air filter; fuel filter (if fitted); new blade (optional). 

 

All engines will have a model code and date stamped somewhere. Briggs and Stratton stamp their codes into the metal valve cover at the front of the engine. Kohler have a tag and Honda have sticker on the engine.

 

After you find these numbers, buying the tune-up kit on line is easy. If you can't find the code, no problem, remove the air filter and match it against a tune-up kit listed on line. Most mower engines are common, you won't have a problem getting a tune-up kit to match. 

 

I wrote this simple guide that walks you through the whole process - "How to Tune-up your mower".

 

 

Mower tune-up kit

Tune-up

Tune-up once per season at the start of the season.

If your mower is new, change the oil after the first 5 hours of use.

Tune-up Kit


Mower tune-up kit

Tune-up once per season at the start of the season.

If your mower is new, change the oil after the first 5 hours of use.

Carburetor Cleaning

Okay, I will assume you have tried cleaning the fuel bowl as per the above guide without success. Now you 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.

 

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

 

Preperation

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 carburetor is corroded, go ahead and replace it. 

 

Remove


Mower air filter

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

Loosen


Mower air filter housing

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

Photo


Mower carburetor

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

Remove


Mower gas line Mower breather pipe Mower carburetor gasket Mower carburetor

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

Strip


Mower Carburetor Mower Carburetor Mower Carburetor

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 carburetor. 

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

Jet


Mower Carburetor Mower Carburetor Mower Carburetor 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. 

Clean


Mower Carburetor Mower Carburetor Mower Carburetor jet Mower Carburetor jet

Use carburetor 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 carburetor 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!

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
Mower air filter cover

Remove

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

Photo

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


Mower carburetor gasket
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 carburetor 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 carburetor in one hand, turn it sideways to release the throttle link, spring and choke lever.

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 carburetor. 

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


Mower carburetor Mower carburetor Mower carburetor

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

Cleaner

Use carburetor 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 carburetor 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!


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

Gas Flow Test

This section deals with a lack of gas flowing from the carburetor. The areas for consideration are: gas cap; gas tank; fuel lines; fuel filter; carburetor float needle seal.

 

If your carburetor 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 carburetor.

 

 

 

 

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.

Vented


Mower gas cap

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

Faulty


mower gas caps

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.

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.

 

 

 

 

Inspect


mower gas tank mower gas tank mower gas tank

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.

Vented

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


mower gas cap
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.

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.

 

Flow


mower gas flow mower gas line

Check flow, and walls for cracking and leaks.

Flow

Check flow on lines.


Ride-on mower starter
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.

 

 

 

Inspect


mower gas tank mower gas filter mower gas line

Check the fuel filter, common types are:

Tank filters are a mesh screen in the bottom of the fuel tank. They can be cleaned and reused.

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.

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

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 carburetor, no flow suggests a filter/gas tank block.


Mower gas filter Mower gas filter Mower gas filter

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. 

 

 

Inspect


mower carburetor float mower float mower float, needle and bowl

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

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

Failure


Mower carburetor cleaning Mower carburetor cleaning

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

Blow some carburetor cleaner into the needle seat on the carburetor.

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

Failure

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

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


mower carburetor float mower carburetor float mower carburetor float
mower carburetor mower carburetor

Spray

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

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

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