Petrol lawn mower troubleshooting. Here s Why Your Lawn Mower Won t Start And What To Do About It

15th August 2023

Here‘s Why Your Lawn Mower Won’t Start And What To Do About It

Standing in your garage with a dead lawn mower, a phone browser open to Google, and the vast untamed landscape of small engine troubleshooting before you, it can be easy to get discouraged. After all, just about anything that prevents a lawn mower from running well can also prevent it from starting. Let’s simplify all these possibilities and zero in on common starting problems, and ones that you’re likely encountering.

Of course, your situation could include all manner of devices thought of as mowers. You could have a simple push mower, or maybe an electric start push mower. But, you could also have a riding mower, an electric mower, or a zero-turn mower that costs more than a Chevrolet Spark. You might even have a tractor towing a rotary cutter like a Bush Hog, in which case you’re probably not reading this article. We’re going to take a look at the most common: push mowers and riding mowers. Your electric mower is essentially always started, and your licensing agreement might prohibit your working on your own tractor. We also won’t deal with zero-turn mowers directly, but obviously a lot of the info for small engines in general will apply to zero-turns. Let’s dive into some of the reasons your mower may not be starting, and what you should do about it.

Ignition system problems: spark plugs

At some point — possibly when the words we have ignition from the Kennedy Space Center Firing Room — many of us began to think of the word ignition as synonymous with starting, but that’s not exactly what’s going on with ignition systems. An ignition system is actually about producing a spark that ignites a fuel-air mixture within an engine’s cylinder(s). Ignition happens continually when you’re using a mower. A few components of this system can be culprits when an engine won’t start.

The most common culprit is probably a spark plug that needs cleaning or replacement. Buildup from a constantly exploding engine cylinder will eventually degrade the performance of the plug until it can’t function properly at all. It’s a little easier to diagnose a bad spark plug in an engine that will barely start than one that won’t start at all, and if you’ve recently noticed that your mower makes you pull the starter rope harder, is prone to losing power while running, or starts using more gas than normal, the plug might be the problem. The clearest sign of plug trouble is when your engine will turn over but not actually start.

It’s a good idea to replace them at least once per year, and cleaning or replacing your plugs is a reasonable first step in resolving just about any starting problem. You can try gently cleaning a spark plug with fine-grit sandpaper, a file, or a soft wire brush, and you can use carburetor or plug cleaning spray to help. Just be gentle; damaged plugs will not be kind to your engine. There are other potential plug issues (wrong plug, bad gapping, or a cracked insulator) that might not be worth diagnosing, given that replacing the plug with a new (and correct) one addresses all these issues at once.

Ignition system problems: plug wires and coil

After dealing with the plug, it’s just about time to get serious with your diagnostics. But first, inspect your plug wires for obvious wear or damage. If they appear to be in poor shape, they probably are, which makes replacing them a good idea regardless of whether they are the full cause of your starting troubles. Next, it’s time to verify that your engine isn’t getting a spark. Ground your plug’s threads against a metal part of the engine itself and have someone attempt to start the mower as you observe the plug. If you consistently don’t see a spark, you should start looking at other possible causes.

If your plug wires are in good shape, ensure they’re making good contact with the spark plugs. Clean their terminals and, if necessary, squeeze the terminals slightly with pliers. If your mower has an on/off switch, use an electrical tester to make sure it’s functioning. Switches on mowers with pull cords can be slightly tricky to diagnose, so it might be a good idea to check the on/off function with a multimeter set to continuity mode. The point is that the continuity should change when the switch changes from on to off; some switches might close a circuit when on while others might open the circuit, but there should definitely be a change when the switch, well, switches. Check that the coil control wire connecting the engine to the coil isn’t abraded; if it shorts to the engine, the mower won’t start or run. Finally, consider replacing the coil. These are not user-serviceable, but they are affordable and critical to starting and running your mower.

Batteries die for a living

By far the most common element of the ignition system that can prevent a riding mower’s starting is the battery. Almost 20% — 11.8 million — of Google’s search results for the word battery include the phrase dead battery, because that’s what batteries fundamentally do: expend all their energy and die. And lawn mower batteries are almost always flooded lead acid batteries, which die more easily and more thoroughly than any other sort.

A lot of the work of fixing a battery problem is the same as properly maintaining the battery to begin with. That is, it’s stuff you should do regularly anyway. So, clean the battery terminals with a wire brush (clamp-on terminals might require a special type of brush, often cone-shaped). Use battery terminal cleaner if it’s necessary, though it rarely is. Make sure all electrical connections are clean and tight. Batteries that haven’t been maintained with a trickle or Smart charger while in storage, such as over the winter, will probably need to be charged and will sometimes even need to be replaced. If your battery is in good condition, check out your alternator and starter. Testing an alternator is simple on equipment with working headlights, as many riding mowers have. Just observe the lights. If they don’t dim when you turn off your engine, you probably have an alternator problem.

After verifying that you have a fully charged battery and a working alternator, check all the wires connected to the alternator and starter for damage. (You can test them with a multimeter if you’re suspicious of their condition.) If everything else checks out, test your solenoid and starter switch using the procedures outlined in this Briggs Stratton guide.

Fuel troubles

Every now and then you’ll see news about a possible perpetual motion machine devised in a scientist’s lab (or mind), but until you can pick one up at Home Depot, you’re going to be dealing with fuel for your lawn mower. This usually means gasoline, and there are a few common points of failure small engines can experience when trying to get fuel from the tank to where it’s needed for internal combustion.

First, make sure you have gas in the tank to begin with. This gets overlooked more often than you might guess, especially when you’re already half-expecting other mower problems and your brain primes the pump by framing everything in that context. Next, examine the age of the gas in use. Did you buy the mower used? Has it been in storage for more than a couple of months? Has the gas itself been sitting in the gas can for a while? Gas can go south in as little as a month, so if someone’s telling you it can sit for two years (a common number in mower lore) without chemical assistance or consequence, you should take your maintenance advice from someone else.

Mowers should be stored without gas or with an added fuel stabilizer (the aforementioned chemical assistance), to prevent such issues. Old gas clogs and damages fuel lines and carburetors, and won’t start an engine very well even if it makes it to the right place. If you already have old gas in your mower, you might need to remove and clean the fuel system components, as described here by Simple Green.

Fuel troubles: the fuel system

Replace your fuel filter regularly, especially if you’ve had old gas in your engine. If your engine has a fuel pump — and it probably does — it will reside between your fuel tank and the carburetor. When you’re out of options, check that it’s actually pumping by using a guide, like this one from Hello Practical.

There’s also the possibility that you aren’t availing yourself of some aids many lawn mowers have built into them to ensure the proper fuel/air mixture makes it to the engine. First, there’s the priming bulb: usually a clear, rubbery protrusion near the carburetor you can press. It will fill itself with fuel, injecting the fuel system with additional fuel as needed for starting.

You should also learn to use your engine’s manual choke feature properly, if it has one. Many newer engines have an automatic choke, and mowers generally have either a choke or a priming bulb, as they both perform the work of enriching the fuel/air mixture for starting your engine. Start your engine with the choke on, then move it to the opposite position once the mower is running properly. Leaving the choke on will stall or potentially damage the engine. Also, check to see if the tiny hole in your gas cap is clogged. That hole creates a vent to allow fuel to move down the fuel lines, and if it’s clogged, your engine will be starved of fuel.

Air filters

Of course, when it’s time for things to blow up inside your engine’s cylinders, gas is only half of the story. Your choke (if you have one) tells the other half: You also need air to mix with the gas, and some mechanisms to help with the mixing. The choke makes the fuel/air mixture richer by restricting (temporarily) the flow of air through the carburetor. Once the engine is running, you should return the choke (and, thereby, the airflow) to normal. But there are a few possible reasons you might continue to have airflow problems.

The first is a dirty air filter. Like most parts of a lawn mower, the air filter is prone to becoming filthier than seems possible. This means it’s doing its job, and it also means the filter requires cleaning or replacing from time to time. A dirty air filter will cause an engine to misbehave in all manner of ways, including not starting easily or at all. Your mower has one or two filters, any of which may be either foam or paper. It’s usually better to replace a paper filter if possible, but otherwise tap it against a hard surface and blow it out gently from the inside with an air compressor.

Foam filters are a bit more involved. Start by tapping and blowing it out like a paper filter, then spray it thoroughly with a filter degreaser and allow to soak for 15 minutes. Rinse under clean running water and allow it to dry, and then apply a filter oil spray. To the extent it’s possible without damaging the filter, squeeze the filter to work the oil throughout. After a few minutes, reinstall the filter and wipe away any excess oil.

air: carburetor

Sometimes your fuel/air mix is off because the carburetor isn’t doing its job properly. In extreme cases, this could prevent the engine from starting. At that point, you must choose between cleaning and rebuilding the carburetor. Fortunately, these processes are mostly very simple. The standard process for cleaning a carb is to remove and clean (or replace) the air filter, then inspect the carburetor inside and out for stray debris. Finally, spray carburetor cleaner into the carburetor while the engine is running, per directions on the spray can.

If this doesn’t work — perhaps because the gum and gunk inside the carburetor is extreme as a result of age or being run with old gasoline — removing and rebuilding the carb isn’t as scary as it sounds. It’s basically a process of taking the carb off and then cleaning everything off of it that you can. It’s also a good idea to take some photos along the way, so you can be sure of how everything goes back together. Finally, just reassemble. Briggs Stratton has a good online overview of this process.

If this makes you too nervous, try adding a cleaning mixture of 4 ounces Sea Foam Motor Treatment and 8 ounces gasoline to the tank. Remove the spark plug(s) and then prime and crank or rope-pull the engine to draw the mixture into the carb. Allow it to sit 24 to 72 hours, then run the engine per Sea Foam’s instructions.

Odds, ends, and tips

There are a few other fairly common situations that can interfere with starting a mower. It’s never a bad idea to change your oil, but be sure to do it properly. Old oil, insufficient oil, overfilling with oil, or using oil that’s the wrong weight (viscosity) for the temperature outside can all contribute to difficult starting.

Keep your mower deck clean; an overabundance of grime and debris can slow blade rotation and hinder starting. Similarly, if you’ve run into something recently with your mower, inspect the mower deck to make sure the blades can rotate freely. A blade striking the deck can prevent the mower from starting altogether.

Finally, there’s the unpleasant business of the starter rope — that thing you yank on a mower with a recoil starter. There are two types of mower owners: those who have cursed the fortunes and questioned the character of mower manufacturers for inventing the recoil starter, and those who haven’t used a recoil starter at all. Common causes of starter rope problems include overfilling with oil and debris interfering with rotation in the mower deck, as mentioned above. Similar problems include bent mower blades and damaged mower deck shrouds. The cord may also be difficult to pull because the flywheel brake (controlled by a bar you must hold while using the mower) is stuck. Try loosening or tightening the cable, then repeatedly open and close the bar that engages the flywheel brake. If this doesn’t work, you might need professional assistance. If you feel up to it, Briggs Stratton has flywheel brake replacement instructions. Similarly, a hydrolocked engine (one that has seized after getting water in the engine) will normally require professional help, unless you’re up for these steps from Garden Guides.

Problems that aren’t (exactly) problems

Sometimes you’ll hear that the cause of some problem is a feature and not a bug, but the distinction isn’t helpful if you can’t start your lawn mower. The best example of this is a mechanism called a safety interlock (or often safety switch), by which your mower won’t run because some other thing isn’t quite right. For example, riding mowers that won’t start unless you’re sitting in the seat. Some cars have interlocks that prevent you from operating them if you’ve had a few beers, but fortunately mowers don’t have this feature yet, as it would prevent about 90% of Saturday afternoon lawn mowing from happening at all.

The safety switches on most riding lawn mowers include a seat switch that will not allow the engine to run unless the seat is occupied; a PTO safety switch that might prevent the blades from turning in certain situations and prevent the mower from starting when (for example) the blades are engaged; a brake switch to keep the mower from starting unless the brake is applied; and a reverse switch, that prevents mowing. Obviously several of these can prevent an engine from starting if they malfunction.

It might be tempting to disable some or all of these safety switches. Don’t — they’re there for good reasons. Unless you’re handy with a multimeter and circuits, dealing with faulty safety switches might be another job for a professional.

Troubleshooting guide

So, how do you know which of these problems is preventing your mower from starting? Let’s look at a few questions that will help you narrow down the most common problems and their solutions. If your mower is full of fuel but only runs for a few seconds, check the pinhole vent in your gas cap for obstructions. This could also be a sign of old gasoline. If the engine hasn’t been run in more than a month, treat the gas as suspect. You might also clean the carburetor and clean or replace the spark plug(s).

How to Fix a Petrol Lawnmower that Won’t Start

If your engine sounds like it’s cranking, but won’t fully turn over, you might have an electrical problem — possibly the starter. If you hear a clicking sound but nothing else, that similarly suggests starter, battery, or related problems. If you don’t hear anything at all when you turn the key, check the starter solenoid and its connections. This also might indicate issues with the battery, coil(s), ignition switch, or safety interlocks. Hearing nothing at all could also indicate that your mower is refusing to start because it is low on oil.

If the engine is cranking slowly, you probably have a failing battery. Check the battery and alternator. If your pull cord is difficult to pull, check that the flywheel brake is disengaged. Be sure you don’t have too much oil in the engine, and that it’s the correct weight for the season. Another sign the engine might be overfilled with oil is the presence of blue or white smoke when it does run. Black smoke, on the other hand, indicates the fuel mixture is too rich. Replace the air filter and check the choke mechanism.

How to fix a self-propelled lawnmower? How to diagnose with fixes

Self-propelled lawnmowers are a class higher than push mowers. They are perfect for yards up to ¾ acres. Unlike a push mower, they push themselves forward. They reduce fatigue caused by push mowers, particularly when you have a challenging yard. Some models offer both front and rear wheel drives and require only steering by the user. Such mowers have a gear transmission system and related components. If you face any issue or the mower does not move, the same transmission system must be checked. In this article, we will take you through the steps of how to fix a self-propelled lawnmower. Mostly, the error lies with the geared tires or transmission. Continue reading for a detailed insight on individual components.

How to fix a self-propelled lawnmower. How to diagnose with fixes:

To fix the self-propelled lawnmower, you will have to check individual components to find the error source. First, check the gears in the drive wheels. If they look bad, you have to replace them. Check the drive belt. If it is not tight or slipping, you need to adjust it. If it looks bad, replace it. Check the transmission box if the gears are connected, and the drive wheels move freely. Check the drive cable. If broken, fix it.

Self-propelled lawnmowers significantly reduce the human energy needed. Although the gear locking and drive belt mechanisms are quite sturdy, they may also face issues from time to time. Usually, a stuck self-propelled lawnmower will have problems related to its driving tires. They may not be working as they are supposed to. Occasionally, one may notice a fault in the drive belts responsible for the efficient transmission system. Fixing them may seem technical, but it is relatively simple. The problem can often be solved at home with some simple fixes, adjustments, or replacing some parts.

General Guide:

There are a few things you have to be careful about. You should precisely know what the error is and which part the error links to. When you have found that out, follow the following steps in order. Keep an eye on the user manual for information regarding various parts.

Step 1: Gather the following tools

As all mechanics say, if you have the right tools and knowledge, consider the job half done. So, leave the technical solutions of problems to use, and you gather the following tools to make the task easier:

Pliers
Adjustable wrench
Screwdriver
Wooden block
Safety gloves

Step 2: Park on a leveled surface and remove the spark plug

Park the lawnmower on a well-leveled, even surface before starting with diagnosing the problem. Disconnect the spark plug cable to ensure that the engine can not unintentionally start. If you have an electric lawnmower, disconnect the mains cable. In the case of a cordless electric lawnmower, remove the batteries. Also, apply the parking brakes so that the mower doesn’t move forward. Turn the ignition off and let the mower cool down before you start. Use a well-aerated and lighted space to FOCUS better.

Step 3: Check the drive wheels

The first step in fixing the self-propelled lawnmower is to check the condition of the drive wheels. But before that, you have to find out the drive wheels as they may be front or rear-driven, or even both. A clue to indicating them is that they will have the transmission box placed near them. One of the most common issues with such a mower is due to these drive wheels. Choose the wheel from one side. Remove it by unscrewing the nut at its center. You may use a socket wrench or pliers.

Hold it in your hand at some angle and check the gears on its inside. They are most likely to be eaten out if the lawnmower does not move. You cannot repair these flat gears, so it is better to replace them. Buy a matching tire depending on your mower brand and model. Screw it back so that it locks in the driving gears of the transmission. While you are at it, rotate the driving gears from the transmission system that connects with the tire. They should move freely, otherwise grease them. If the problem persists, you will have to check the drive belt. Then, repeat the process for the other drive wheel. The tire will no longer slip.

Step 4: Check the drive belt

Check the drive belt of your mower. Check if it is slipping, the belt condition, and whether it is wound over the pulleys correctly. Lower the mower deck to the lowest stage possible. Turn the log lever present on one side of the steering wheel towards you to disengage the blades. Next, raise the mower on some platforms and examine from below.

Now, examine that the belt should be passing over the pulleys. There should be no sags, and the belt should be perfectly tight. If it is not, you need to adjust it. Locate the drive cable that originates from the drive control panel and comes down to connect with the transmission panel. There will be a metal bracket here that holds the connection between the belt and cable. Unbolt the bracket, pull it away from the belt so that it gets stretched. Now, tighten it at this spot. Check the belt’s stretch over the pulleys again. Turn the log ever to engage the blades. Put the mower deck back in its place.

Step 5: Check the transmission box

The transmission box is a metal compartment that lies on top of the drive wheels. It contains the components that deal with driving the wheels. The drive belt, gear mechanism, and cable drive all connect here. The engine piston drives the transmission box through the drive belt. The gears convert the high RPM and low torque from the engine into a low RPM and high torque that propels the mower. The box itself is quite complex, and there are only a few things that you can check yourself.

Check that the belt drive is connected correctly and moves freely. Check whether the gears that connect the drive wheels move freely. If the gears connected with the belt are worn-out, then the error lies there. Check their condition by removing the box cover with a screwdriver. Check the drive cable’s connection too. If the error lies in the transmission box, you can locate it at most. It is quite complex, so better to get it repaired by an expert.

In any case, you would have solved the most major problems by now. Reconnect the spark plug cables, turn the ignition on. Start the mower and let it run for a while to lubricate all the parts.

Precautionary Measures:

Some things that you have to check before working on your lanwmower:

Safety gloves: Use safety gloves when you work with sharp or hot lawnmower parts. You also protect your hands from grease and oil spills.
Use quality parts: Try to use quality parts. This can mean good OEM parts or genuine parts that the company recommends.
Disconnect the battery: Disconnect the battery before working on your lawnmower. It is easy to create a short circuit that can harm your battery and other electrical parts.

Final Remarks:

Self-propelled lawnmowers are one special type of mowers that pull or push themselves, or both if you have a four-wheel-drive system. They only require two things from you: guidance while mowing and proper care and maintenance. If your lawnmower loses its power or the tires slip or does not move, you have to check many parts to pinpoint the error. Check the drive wheels, drive cables, and transmission system, which is the most common cause of the trouble. In this article, we have explained step-by-step the details to fix your self-propelled lawnmower at home. This particular type of lawnmower is a bit complex having that well-intricate design. So, in case your problem does not solve, take it to an expert on the machine.

Small Engine Carburetor Troubleshooting – A beginners guide

Small engine carburetors don’t handle bad or dirty gas very well; if you own a small engine, you’ll encounter carburetor problems at some point. In this guide, I’ll cover the main problems with small engine carburetors and the solutions.

So how do you troubleshoot a small engine carburetor? The most common issue with all small engine carburetors is gumming (old gas); cleaning the carb usually solves the problem.

Typical carburetor-related problems include:

Tank – Outlet hole inside the tank blocks with grit stopping or slowing fuel flowing to the carburetor
Cap – Cap allows the tank to breathe; when the cap vent fails, it seals the tank stopping fuel flow
Lines – Leak at connection points and on occasion can block stopping fuel flow
Tap – Leak, causing fire risk
Fuel filter – Block or slow fuel flow to the engine
Pump – Fail causing a no start (Not fitted to all mowers)
Carburetor – Block, under fuel and over fuel causing no start or poor running
Fuel solenoid – Fail, stopping fuel flow (Not fitted to all mowers)
Intake manifold – Leak, causing engine surging
Dirty refueling can – Often the source of the dirt
Air filter – Can block, causing no start or poor running with black smoke

This guide will help you diagnose and fix your fault quickly. Although this guide covers a tractor mower carburetor repair, it will work for all small engine four-stroke engines, as they all run very similar gas systems. There are many components in the fuel system that can cause issues but by far, the most common fault – Carburetor contamination.

petrol, lawn, mower, troubleshooting, here

Very often, 5 minutes spent simply draining the gas bowl fix carburetor problems. It’s all covered here in this post, or you can check out the “Carburetor bowl draining video” and also the “Carburetor cleaning video.”

The videos walk you through the whole process – removing, stripping, cleaning, reassembly, and refitting. A good cleaning and fresh gas fix most carburetor issues.

What Is Gumming?

Basically, it’s old stale gas that turns to a sticky gel; it clogs up the tiny passages of the finely balanced carburetor. Cleaning usually solves the problem, but if it’s bad, don’t waste your time cleaning, go ahead and change out the carburetor.

How Does it Happen?

Ethanol fuel is blended with regular gas, that’s not a problem for cars, but it is for small engines. Typically, the small engine is put away for winter with the gas still in the tank. The ethanol blend attracts moisture, and the alcohol content in the gas evaporates. The result is gumming and rust – it’s a carb killer.

To prevent this from happening, I use a gas stabilizer at the end of the season, mixed with the gas; it’ll keep it fresh for up to 2 years, so next spring it’s pull and mow. I use a product called Sta-bil gas treatment, 1 ounce treats up to 2.5 gallons; it prevents gumming and cleans the fuel system.

Petrol Lawnmower Won’t Start Help.

It can be used in all gas-powered kit including 2-stroke engines. You can use it all season; I only use it at the end of the season and when winterizing. You’ll find a link to the gas stabilizer I use here on the “Small engine repair tools” page.

Of course, not all fueling system faults are gummed-up carburetors – running some simple tests will point you in the right direction.

Gumming – Gas turns to a gel and blocks everything up – ya nasty. When it’s bad, I prefer to replace the carb. Cleaning doesn’t guarantee that you get it all, then you’re tearing it down again.

Replace – Don’t even think about it. Order a new one!

Symptoms Of Carburetor Faults

How my customers describe fuel system faults, one or more of these may sound familiar.

Customer complaints include:

Mower stops for no reason
I put the mower away for winter, and now it won’t start
Engine runs rough
Engine splutters when I cut on a slope
Engine dies when I start cutting grass
Black smoke from the muffler
Engine revs up and down by itself Mower only runs on choke
Mower blows white smoke

If any of these sound familiar, you are in the right place.

Carburetor Fault Finding

At this point, it’s assumed that you have run the Gas Shot Test and Choke System Check, and they both confirmed a fueling fault. If that is the case, your symptom will fit one of the following descriptions:

Mower won’t start; Runs rough; Blowing black smoke; Starts then dies; Surging; Lacks power; Only runs with choke; Gas leaking into the oil; Blowing white smoke; engine revving up and down by itself; Mower only runs on choke”; Mower blows white smoke.

OEM – Carburetors aren’t expensive or difficult to fit. Sometimes it’s better to just go ahead and replace the whole unit. Carburetors do wear out, and I replace lots of them.

Fuel Solenoid

A fuel solenoid is an electromagnetic valve that simply opens as you turn on and run the mower engine. When the valve is in the open position, it allows gas into the engine.

The purpose of the valve is to close at shutdown and prevent gas leaking into the engine, which helps prevent engine run-on.

Not all mowers will have one fitted, but if you have, it will be easy to spot. It lives on the bottom of the carburetor bowl and has an electrical wire and connector fitted.

To test the solenoid, turn the ignition on (without starting the motor), locate the sensor, and disconnect the wire; now, reconnect and listen for the click sound. If you don’t hear a click, you could have a solenoid failure or a power supply problem.

Removing the solenoid is the best way to test; that allows you to see it actually open and close. If you have a power supply problem, use a DVOM or test light to check for power.

If the solenoid fails, the mower won’t start, and a failing solenoid will cause problems like, only working when it wants to, or shutting down the mower. Changing out the solenoid is easy.

Test – Remove the connector to test for the click sound, or use a test light to check for power. Briggs and Kohler’s solenoids are shown here.

Fuel Bowl Clean

In some cases, you may only need to drain the fuel bowl. In other cases, you will need to remove the carburetor and clean it thoroughly. Your carburetor may look different, but the process is the same.

In this part of the guide, I will drain just the fuel bowl and check the fuel flow. You can find your fuel bowl behind the air filter. You don’t need to remove the air filter housing to access the bowl.

Remember, if your ethanol gas is much older than one month, it’s stale. Cleaning the bowl won’t make it go. You need to drain the tank, and carburetor bowl and fill them with fresh gas.

I use the Briggs and Stratton oil extractor to remove stale gas and grit from the bottom of the gas tank; it’s easier than removing the tank. Check out the one I use here on the “Small engine repair tools” page.

If this works out, great! If not, I wrote this guide, which will walk you through the whole process –“Remove Clean Carburetor”.

Alternatively, it’s all covered in this video, from bowl drain and cleaning, complete carburetor removal, stripping, cleaning, rebuilding, and refitting. It’s all covered here “Carburetor cleaning video”.

Carburetor Bowl Draining

Locate – The carburetor is located behind the air filter, and you usually have enough room to work without removing any other components. Turn the gas off; if you don’t have a tap, use grips to squeeze the line.

Remove – This type of bowl doesn’t have a solenoid. Remove this bowl by removing the bowl bolt. An O-ring gasket is used to seal the bowl to the carburetor. Usually, it stays on the carburetor side, and that’s OK; you can leave it there. Clean the bowl, and when refitting, uses some lube on the o ring seal to prevent pinching.

Remove – This carburetor has a fuel solenoid. To remove it, disconnect the wire connector and use an open-ended wrench between the bowl and the solenoid.

Sometimes you can just turn the bowl by hand. Remember to lube the gasket when refitting the bowl. Often no matter how careful you are, the bowl gasket will leak gas; if so, the only fix is to replace it.

Remove – Remove the fuel bowl drain bolt, which on some models is also the fuel solenoid. Your bowl may have a bolt or two screws, and in some cases, the whole bowl will come off. Allow the fuel in the carburetor to drain out, catch it in a suitable container, and have some old rags handy. If you have any doubts about fuel quality, drain the tank and fill it with fresh gas.

Testing Fuel Flow

Flow – The carburetor bowl type with two screws can be tricky to remove, so if that’s your type, just remove the solenoid, allowing the gas to drain, reassemble and test. Often this is enough to fix the problem. But before you reassemble, check the fuel flow on whichever type of bowl you have. Turn the fuel on. If fuel flows – Refit the fuel bowl bolt and test the mower. If there is no fuel flow, we’ll need to dig a little deeper.

If you removed the fuel bowl or drain bolt and found no fuel flowing, or the carburetor needle is leaking gas even with the float in the shut-off position (Up), then this guide will help you. This guide works just the same for walk-behind mowers, lawn tractors, ride-on mowers, tillers, snow blowers, or any 4-stroke small engine.

Riding lawn mower fuel systems are either gravity feed or pump feed; your mower will be one or the other. You will be able to identify which system you have by following the fuel line from the fuel tank. Go ahead and identify your system, and carry out the checks as directed.

A weak carburetor float needle is a common problem, it causes gas to flood the engine oil, it’s known as Hydro-locking, and we’ll deal with it first before looking at identifying your fuel supply system.

Hydro-locking

Gas leaks into the cylinder, when the mowers are not in use, filling it right up. This prevents the engine from cranking over because the piston has no room to move. Some owners think that the battery is flat, and try jump-starting without success.

Other tell-tale signs of hydro-locking are a stink of gas in the garage, gas on the floor of the garage, mysterious loss of gas from the tank, and a very high oil level that stinks of gas.

Some mowers may start when most of the gas leaks from the cylinder into the oil. The operator then notices lots of white smoke, rough running, stalling, and oil leaks.

The fix – replace the whole carburetor, because often just replacing the needle seal doesn’t work. Fitting a gas tap, and turning off the tap when the mowers are not in use will prevent future problems. But it’s important to change the engine oil; it’s diluted and contaminated by the gas.

This guide will show you how to fit a tap and the tools needed – “Fitting a gas tap.”

Identifying your fuel supply system

Gravity Fuel System – Identified by a fuel line from the tank runs to a fuel tap, through a fuel filter, and onto the carburetor. (Tap may not be fitted) This system is prone to leaking gas into the oil and causing a condition known as hydro-locking.

Pump Fuel System – A fuel line from the tank runs to a fuel tap, then a fuel filter, then a fuel pump, and finally to the carburetor (Tap may not be fitted).

Fuel Supply Troubleshooting

Remove Gas Cap – A gas tank needs to breathe; when fuel leaves the tank, it needs to be replaced with air. A sealed tank will prevent fuel from flowing. Make sure you have gas in the tank. Remove the gas cap and check the flow. Check the fuel tank for grit – the outlet hole is small and blocks easily. You may have to remove the tank to clean it thoroughly.

Filter – Examine the fuel lines from the tank to the carburetor, checking for kinks or damage. Some fuel filters will be a see-through bottle type; if it’s dirty – Change it. Arrow to carb.

Remove – Remove the gas bowl – when the float is in the dropped position, the gas should flow.

Needle – Remove the float and needle, and check the condition. A worn needle turns pink in color. The needle seals the flow of gas when the float is in the up position. A worn needle can block the flow or cause gas to leak into the oil. When this happens, I prefer to replace the complete carburetor.

Spray – Blow some carb cleaner into the needle seat on the carburetor. Still, no flow – Remove clean the carburetor; consider replacing the complete unit. Some carburetors have the seal on the tip of the needle, and others have the seal in the carburetor. Carb was removed for the demo.

Gas Pump – The pumped system is, as said, very similar. Check that the gas filter supply to the pump is OK. The fuel pump operates by the pulsing of crankcase pressure which is supplied by the hose pipe seen in the center of the picture. Check this pipe is secure and undamaged; sometimes, they perish.

To test the pump – Remove the output line on the left and crank over the engine. No fuel flow – Replace pump.

Remove Clean Carburetor

Okay, I will assume you have tried cleaning the bowl as per the above guide without success. Now you need to remove the carburetor and clean it.

Only basic tools are needed, but a can of carburetor cleaner makes life a whole lot easier. In the workshop, I use WD40 cleaner; check it out on “Small engine repair tools” page. A container for nuts and bolts, some rags, and take lots of pictures to help you remember where levers, gaskets, and springs go.

Your carburetor may not be the same as the one used here, but yours will look very similar, and the process is the same.

The whole process is covered in the “Mower surging video” and if you need to replace the carburetor, check out the Amazon carburetor link below.

Remove – Remove the air filter and engine plastic cover.

Remove – Remove the choke cable.

Turn off the gas and remove the fuel line. If you don’t have a gas tap, use grips to gently squeeze the line.

Remove – Remove the intake pipe.

Remove – Unplug the solenoid valve and remove both carburetor bolts.

Remove carburetor fasteners

Photo – Take note of linkage, spring and gasket locations, and orientation before removing.

Teardown

Remove – Remove the float by sliding the pinout and removing the needle. When worn, the needle seal turns pink. Carburetor kits will include new bowl gaskets and needle seals.

Remove – When removing the fuel/air mix screw, count how many turns it takes to remove it and refit to the same number.

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

Remove – The dirt collects in the emulsion tube; it houses small portholes through which fuel flows.

Clean – Clean the jet and emulsion tube really well, the portholes may not look dirty, but a build-up around them makes them smaller and restricts gas flow. Use a strand of wire from a wire brush and run it through the holes.

Check – The bowl gasket may be distorted or perished. Over-tightening or pinching will cause it to leak. To avoid damage, lube o ring on reassembly.

Spray – Use a good quality carb cleaner and compressed air if available. Spray all passages and portholes.

OEM – A new carburetor makes a bit of difference; cleaning won’t guarantee it runs sweet. So, if cleaning doesn’t work out, go ahead and treat your mower to a new carb.

Finally – When rebuilding, replace the gas filter. Clean your gas can and fill it with fresh gas. If you’re storing the mower for periods longer than a month, use a gas stabilizer. It will prevent gumming.

The Ultimate Guide: Troubleshooting Your Lawn Mower When It Won’t Start

An engine is a powerful machine that needs three essential things to work: fuel, air, and a spark. The fuel, often petrol or diesel, provides the energy, while the air provides the oxygen necessary to burn the fuel efficiently. The spark, created by a spark plug, ignites the fuel and air mixture, causing a small explosion that makes the engine’s parts move. If any one of these three elements is missing – fuel, air, or spark – the lawn mower won’t start and run. These three components are equally necessary to start the engine and keep it running.

An engine is a carefully orchestrated machine, where all the parts must work together seamlessly for it to function properly. Clogs and blockages in the finely tuned moving parts can prevent the engine from working, just like a small pebble can jam a complex clock’s gears. The other parts of an engine have important roles too. Some create high voltage needed to make the spark needed to ignite the fuel, while others filter the air and fuel to ensure a smooth and efficient burn. There are also safety components that protect the user from potential harm. All these parts must be set correctly and work together harmoniously to keep the engine running and the user safe. Regular maintenance of your lawn mower will ensure your lawn mower starts properly every time. This guide will cover 99% of the problems you might encounter when starting your lawn mower. If it still doesn’t work, maybe you should consider a new model – here you’ll find the top 5 petrol lawn mowers?

Operator Presence Control (OPC) also known as “Dead man’s switch” or “Dead man’s handle”

The Operator Presence Control (OPC), also known as “Dead man’s switch”, “Dead man’s handle” or “engine flywheel brake”, is a safety feature found on many lawnmowers. Its purpose is to ensure the lawn mower’s engine and cutting blades stop running if the operator releases their grip on the handle. This safety mechanism helps prevent accidents and injuries, especially when the operator loses control of the mower or needs to stop the machine quickly. To troubleshoot the OPC, first, make sure you have moved it to and are holding it in the “run” position. Next, check for any visible damage or wear on the switch or handle. Ensure the cable connecting the switch to the engine is properly attached and not broken. The OPC is a crucial safety component that ensures the safe operation of a lawn mower, protecting both the user and those around them, and it should not be bypassed.

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Fuel

Fuel is a critical component of a petrol lawnmower’s operation, and several issues can arise if it is not managed correctly. One common problem is that fuel may not reach the engine due to a clogged air/fuel filter or a malfunctioning carburettor. To solve this, tap on the carburettor to let the fuel flow through to the engine and check for clogged filters.

If the fuel filter or carburettor becomes clogged, it may prevent fuel from reaching the engine. In this case, the old fuel from the float bowl should be drained, and the carburettor should be thoroughly cleaned. If these steps do not work, the carburettor may need replacing.

Sometimes, the fuel cap can also cause problems. Without a vent, a partial vacuum forms in the fuel tank that eventually stops the flow of fuel. If the mower sputters and dies after a few passes, it could be due to the fuel cap. You should remove the gas cap to break the vacuum and then reattach it. If the mower does not start or cuts off again after a few minutes, a new gas cap may be necessary.

You should always make sure you purchase the correct fuel for your lawn mower.

Old or stale fuel

One of the most common reasons why petrol lawnmowers won’t start initially is due to old or stale fuel. Petrol is an organic hydrocarbon and like all organic substances, it breaks down naturally over time. Gasoline has an ideal shelf life of about 30 days due to the ethanol it contains. If left inside the lawnmower for longer than this period, it can cause corrosion inside the machine and even clog the carburettor. Most people forget this and assume all is well when they see leftover fuel in the petrol tank. This can lead to unnecessary checks and changes.

To avoid problems with stale fuel, remember to replace the petrol inside the lawnmower every 30 days or so. You can also use a fuel stabilizer to keep petrol fresh for up to 3 years. However, fuel stabilizers cannot revive stale fuel. If the fuel in your mower is more than 10 to 12 weeks old, drain it and replace it with new, fresh fuel. Do not refill it with fuel from a jerry can because it is probably as old as the fuel in the mower itself. Instead, replace the whole lot with new fuel from the pump and only buy fuel you will use within a few weeks of purchase.

Check the Air Filter

A common issue that can prevent a petrol lawnmower from starting is a dirty or blocked air filter. The air filter guards the carburettor and engine against debris such as grass clippings and dirt. Over time, these particles can clog the filter and prevent the engine from starting.

To check the air filter, open the filter cover and inspect the sponge or paper filter for blockages. If the filter is dirty or torn, it must be cleaned or replaced. Depending on the type of filter, it may be sufficient to tap it regularly and apply some air filter oil.

Cleaning the filter involves washing foam filters in hot water and detergent to loosen grime, allowing it to dry completely, and wiping fresh motor oil over the filter before replacing it in its housing. On the other hand, paper filters can only be replaced.

A clean air filter is essential for the smooth operation of the lawnmower. Without it, the carburettor may be starved of oxygen, causing poor starting, poor fuel economy, and potential engine damage. To keep your mower in good condition, replacing paper filters or cleaning or replacing foam filters after every 25 hours of engine use is recommended.

If your air filter is dirty, cleaning or replacing it can be a straightforward solution. In addition to grass clippings and dirt, some air filters can get clogged with debris, such as leaves. Regular air filter inspection and cleaning can help prevent these blockages and keep your lawnmower running smoothly.

Blade Issues

Blade issues can cause a lawnmower to fail to start. If the blades are jammed or obstructed, the lawnmower won’t gain enough momentum to start. It’s important to check for any blockages around the blades.

Grass clippings can clog the mower deck, particularly when mowing a wet lawn, preventing the blade from turning. If the starter rope seems stuck or is difficult to pull, it’s likely due to a clogged deck. It’s recommended to turn the mower safely off and tip it over onto its side to examine the underbelly for large clumps of cut grass that can be removed using a trowel.

When inspecting the cutting blade, remember to turn the mower over correctly and according to the manual. You should always remove the spark plug cap before working on or near the cutting blade to avoid unexpected starts. Winter grass is tough and can quickly blunt a blade, so it’s essential to keep the cutting blade sharp. A blunt blade will give a poor cut, labour the engine causing engine wear, and increase fuel consumption. Cutting blades spin at high speeds and always need to be balanced. Debris can damage the cutting blade, causing engine strain and leading to costly repairs.

Mower cutting blades can be sharpened and balanced, and owners can refer to the owner’s manual for details or call their local dealer or mower service centre for assistance.

Choke / Flooded engine

The choke is a feature on some lawn mowers designed to assist with starting the engine, especially when it’s cold. To use the choke, pull it out before starting the engine and then push it back in once the engine is running smoothly. Be cautious not to leave the choke on for too long, as this could cause the engine to flood. However, many newer lawn mower models have replaced the choke with a primer. To use a primer, press it a couple of times before starting a cold engine. Be careful not to press it too many times, as overdoing it can also lead to a flooded engine. If you encounter issues starting your lawn mower, ensure the choke or primer is functioning properly and not causing any flooding.

If you suspect that your engine is flooded, don’t worry – there are steps you can take to resolve the issue. A flooded engine occurs when there is too much fuel and not enough air in the combustion chamber, making it difficult for the engine to start. To deal with a flooded engine, first, turn off the ignition and wait for a few minutes to allow the excess fuel to evaporate. Then, open the throttle – if your lawn mower has one – or hold down the primer button to allow more air into the engine. With the throttle open or primer held down, try starting the engine again without engaging the choke. This process should help clear the excess fuel and allow the engine to start. If the engine still does not start after several attempts, consult your lawn mower’s user manual or contact a professional technician for further assistance.

Carburetor

A clogged carburettor is one of the most common issues that can prevent a lawnmower from starting. This can happen when fuel is left in the mower for an extended period, causing some of the ingredients to evaporate and leaving behind a sticky substance that clogs the carburettor. If this is the case, try cleaning the carburettor with a carburettor cleaner. If that doesn’t work, it may be necessary to replace the entire carburettor.

A dirty carburettor can also cause a lawnmower to start and then die or not start at all. The carburettor mixes fuel with air to create the right fuel/air mixture for combustion. If the carburettor is dirty, it won’t be able to draw air into the engine, causing the mower to malfunction. A dirty air filter is often the culprit, as leftover petrol can condense and solidify in the filter, preventing it from pulling in the air. It’s also possible that the carburettor isn’t attached properly and is leaking air after it draws it in.

If you haven’t cleaned the carburettor recently, it’s worth checking again to see if it needs cleaning. Many models have a primer, a manually operated fuel pump near the carburettor that can fill it with fresh fuel in a few pump strokes. This can be especially useful if the mower has been run empty or unused for an extended period. Be sure to check the primer’s functionality with a few pump strokes before attempting to start the mower.

Cables

Damaged or loose cables can lead to various problems, such as difficulty starting the engine or loss of power. To check the electrical cables, begin by turning off the mower and disconnecting the spark plug to ensure safety. Examine the cables for any signs of wear, fraying, or damage, paying close attention to the connections at the battery, solenoid, and starter motor. Make sure the connections are clean, tight, and free of corrosion. If you notice any damaged cables, replace them promptly to avoid further complications.

Check the Spark Plug

Experiencing difficulty starting your petrol lawnmower might indicate a problem with the spark plug, which is responsible for igniting the fuel in the engine. Over time, spark plugs can become dirty, corroded, or disconnected. To inspect the spark plug, first, remove the lead and then carefully unscrew the plug using a spark plug spanner/socket. Examine the end of the plug for any signs of wetness from petrol, which could point to a carburettor blockage. Check the fuel line by removing and blowing through it to ensure it’s clear. If the plug is dry and the fuel line is clear, the issue is likely with the carburettor, which should be cleaned by a professional if you’re inexperienced in handling it.

If the spark plug appears wet or has visible corrosion, burns, or sludge, it’s best to replace it rather than clean it. For cleaning, use a grease-cleaning solution or solvent and gently sand the contacts. Make sure the gap is set correctly, as specified in the user manual. Always have a spare spark plug handy in case of a sudden malfunction.

When inspecting the spark plug, pay attention to the electrode and insulator for any buildup. If present, spray brake cleaner on the plug, let it soak for a few minutes and then wipe it clean. Reinstall the spark plug by hand before using a socket wrench to tighten it. If the problem persists, consider replacing the spark plug.

The spark plug’s condition can also be assessed by unscrewing it from the motor and visually inspecting it. If the electrodes have a metallic or fawn colour without soot, the spark plug can typically be used for another season. Slight discolourations can be removed with a wire brush. However, if the spark plug is black or oily, there may be a defect in the system that needs urgent repair. When purchasing a new spark plug, make sure the type designation is correct, which can be found on the ceramic body. Check the manual to make sure the new spark plug is compatible.

Check the oil

Regularly checking the oil levels in your lawn mower is important to prevent serious damage to the engine. Most lawnmowers have a dipstick to check the oil. Locate the dipstick, remove it, and wipe it off with a clean cloth. Reinsert the dipstick into the engine and remove it again to get an accurate reading for the oil level. Top off the oil if necessary, and ensure you use the recommended oil for your lawn mower. Regularly checking your lawn mower’s oil levels can help increase its longevity, reduce the chance of engine failure, and keep your lawn mower running smoothly.

The correct oil type can be found in the owner’s manual. Using the wrong oil can reduce efficiency and risk permanent damage.

Depending on the age of the engine oil, it may be time for an oil change. For commercial 4-stroke lawn mowers with normal use, it is recommended to change the oil once a year, ideally in the spring. An oil change should occur every 25 operating hours for petrol mowers with heavy use. The first oil change should occur after 5 to 6 hours of operation for newly run-in lawn mowers. These short change intervals compared to a car are because lawn mower petrol engines usually do not have an oil filter, making the oil dirtier more quickly.

Remember that the oil level should be checked not just at the start of the season but at regular intervals to ensure the longevity of the mower’s engine.

Battery

If your lawn mower features an electric start, it relies on a battery to provide the power needed for the engine to start. A charged battery is essential for the smooth operation of your mower. A flat battery could be the culprit if you’re experiencing difficulties starting your lawn mower.

To troubleshoot a flat battery, follow these steps:

Check the battery connections: Make sure the connections between the battery and the mower are clean and secure. Corrosion or loose connections can impede the flow of electricity, preventing the mower from starting.

Test the battery voltage: Using a multimeter, measure the voltage of the battery. A fully charged battery should read around 12.6 volts or higher. If the voltage is significantly lower, the battery may be flat or faulty.

Charge the battery: If the voltage reading is low, connect the battery to a compatible charger and allow it to charge for the recommended amount of time. Consult your lawn mower’s user manual for specific charging instructions.

Test the battery again: After charging the battery, measure the voltage once more using the multimeter. If the voltage remains low despite charging, the battery may be damaged or have reached the end of its lifespan, and a replacement may be necessary.

Check the charging system: If the battery continually loses charge or becomes flat, there could be an issue with the lawn mower’s charging system. In this case, consult your user manual or contact a professional technician for assistance.

Starter Solenoid

The solenoid is an essential component in a lawn mower’s electrical system, responsible for transferring electrical current from the battery to the starter motor when you turn the ignition key. Essentially, it acts as a switch, enabling the engine to start when needed. To troubleshoot a solenoid on a lawn mower, begin by ensuring the battery is charged and properly connected. If the engine still fails to start, locate the solenoid (often found near the battery or starter motor) and check its connections for any signs of corrosion, wear, or damage. Clean and tighten the connections as necessary. If the issue persists, use a multimeter to test the solenoid’s functionality by measuring the voltage at the input and output terminals while turning the ignition key. If the voltage reading does not change when the key is turned, the solenoid may be faulty and need replacement.

Conclusion

The information in this article should cover 99% of the issues stopping your lawn mower from starting. With the help of this article, you will be able to diagnose and repair any lawn mower that won’t start. You’ll learn how to check for spark plugs, fuel lines, air filters, fuel tanks and other possible causes of a lawn mower not starting. Also included are tips on when to replace parts or when it’s time to call in a professional. We hope this article helps you get your lawn mower running like new again!

Please read through each of the troubleshooting steps and be sure to follow all safety precautions before starting any repairs.

Sources:

https://www.housedigest.com/1206567/heres-why-your-lawn-mower-wont-start-and-what-to-do-about-it/
https://www.gardentoolexpert.com/how-to-fix-a-self-propelled-lawnmower-how-to-diagnose-with-fixes/
https://www.lawnmowerfixed.com/carb-troubleshooting/
https://harryrufus.com/troubleshooting-when-your-lawn-mower-wont-start/

Lawn Mowers here, lawn, mower, petrol, troubleshooting