Here’s What To Do If Your Lawn Mower Won’t Start. Ride on mower motor

Learn the reasons why a lawn mower won’t start after winter or during peak season, and how to fix those problems.

Family Handyman

Introduction

Most of the time when a lawn mower won’t start the cause is a problem with the gas or the lawn mower carburetor.

What to Do if Your Lawn Mower Won’t Start

Whatever kind of lawn mower you’ve got, the last thing you want once winter finally lifts and spring has sprung is a lawn mower that won’t start.

If you’ve taken the proper steps to winterize your lawn mower, you’re far less likely to be dealing with such issues. It’s also why you should tune up your lawn mower at the start of every season. However, it’s not out of the ordinary to find your gas-powered lawn mower not starting from time to time, so it’s important to know why your lawn mower isn’t starting and how to fix it.

Project step-by-step (6)

Check the Gas Tank

Let’s start with the obvious. Before you have a heart attack pulling on the rip cord, you’ll want to check the fuel. Like any gasoline-powered engine, lawn mowers run out from time to time. Maybe you forgot it was running on fumes when you finished mowing last time. It sounds simple, but we’ve all overlooked the gas tank from time to time.

Even if there is gas in the mower, if the fuel’s been in there more than a month, that could be the problem. Gas sitting around too long in the tank can get contaminated with dirt and extra moisture.

So if your gasoline has been in the mower for more than month, drain the gas properly, dispose of it correctly, and fill up the mower with new gas. It may take quite a few pulls to suck the new gas into the lawn mower carburetor, so be prepared to clean and dry the plug a few more times.

Add fuel stabilizer when you fill up the tank to help protect the gasoline in there from dirt and moisture.

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Check the Spark Plug

Start by making sure the lawn mower spark plug cable is connected to the plug itself. It’s quite possible that it got pulled off there over the winter while the mower was being stored in the garage.

If that’s not the issue, the next step is to remove the spark plug to see if it’s wet. There’s no way the engine will start if it is. So clean the plug with carburetor cleaner and let it dry. Cleaning it with compressed air isn’t enough; you need a solvent to remove oil residue. If it’s really grimy and dirty, it might be best to change the spark plug.

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How to un seize a riding lawnmower engine

One may face many technical problems from time to time if he owns a riding lawnmower. A seized lawnmower engine is, however, one of the rarest of problems. If you do not want to take your Lawnmower to the mechanic because you fear that he might charge more, don’t worry. This blog will help you distinguish the damaged parts, replace them, and test them, all at a home scale.

A lawnmower engine is usually a sturdy component. A seized engine is usually due to the piston and rings sticking in the bore. With the help of some freeing fluid or cleaner, this problem can be solved. However, there might be other contributing factors to this too. Here we take you through them all.

How to un seize a riding lawnmower engine:

• Step 1: Remove the spark plug
• Step 2: Clean the combustion chamber with some cleaner
• Step 3: Open the head and gently tap the piston cylinders
• Step 4:Check the motor oil
• Step 5: Test the blades and close all the components

We shall provide in-depth details of the steps mentioned above, like what sort of tools you need and any complexities you might face. Please stick with us as we go through all the potential issues and troubleshoot each of them.

Steps to Un Seize a Riding Lawn Mower Engine:

A riding lawnmower engine may get seized after you de-winterize it due to such distant usage. The seized engine may be due to the parts that are stuck or due to the machine’s absence of motor oil. The procedure below explains all the necessary steps to deal with the situation.

Step 1: Remove the spark plug:

Whenever a defect occurs related to the internal parts of a lawnmower, removing the spark plug is the first step. The spark plug is removed before cleaning the rest of the parts for two purposes. One is so that no accident occurs when one is pulling and cleaning the cord. The second is to clean the spark plug itself.

To do this, tilt the lawnmower body to a side so that its side now faces the roof. With the help of a plier, unscrew the spark plug because it may be hard to remove it by hand (seized up chamber). Now, using a feeler gauge, you may check the gap between the spark plug terminals. Compare it with manual reading. Now, either clean the plug or replace it.

Step 2: Clean the combustion chamber with some cleaner:

Through the removed spark plug hole, you can access the piston cylinders and the combustion chamber. You can quickly get aerosol sprays like “Blaster PB” or “WD-40” from a local hardware store. When you buy them, do get yourself a pair of safety gloves as these might be toxic to spray, hence injurious to health. Now, through the hole, flood in an available amount of the cleaner spray and let it rest there for a couple of hours at the least.

The cleaner spray acts as an anti-rust and lubricating agent. It removes the clog built up in the chamber. After a few hours, let the cleaner fluid drain out from the spark plug hole. Now, try to move the blades manually. Make sure that while rotating them, they should be rotated in their natural directions. You will feel lesser resistance to the movement now.

An additional step can be to pull the cord and see the blade’s rotation. This may further give some idea about the extent of seizing in the engine. Pulling the card will produce little motion in the lawnmower blades, a sign for a seized up engine.

Step 3: Open the head and gently tap the piston cylinders:

Sometimes, only using a cleaner doesn’t solve all of the problems as the riding Lawnmower may have been idle for a longer time. In this case, remove the seat to expose the head of the engine. Opening the head with a screwdriver or wrench will allow you actually to see the piston cylinders. The engine may be blocked and may require an internal push start.

So, hit the piston head preferably with a wooden hammer. Tap it gently as it moves down. This pretty much solves the problem. Besides, check the piston rings, lubricate them. Check for any damaged seals, take no risk, and replace them. Clean the cylinders and remove any dirt or debris that has hardened up and is stuck. Throw in some cleaner spray to moisten the dirt and clogged up the oil. Clean it and let it dry for a few hours.

Step 4: Check the motor oil:

We have already taken you through the basics. These were easy to solve. Now, a more complex issue that may require more of your FOCUS is here. In all types of seized activities, the one that is caused by running the engine on an insufficient motor oil spray is the most serious.

Through the removed piston head, disintegrate the crankshaft. Same as before, using a wooden hammer, give the cylinders a strike to thump them out. Also, rotate the crank. This helps remove the crude oil that got stuck up in the moving parts. Use a cleaner to purify them thoroughly.

Remove the connecting rods and seals. Clean them too, as crude oil may still be stuck there. Give the insides a thorough washing. You can use petrol to wash it too. Now, let the engine bask in the sun and dry up naturally. Add lubrication to each component as you close up the casing and side by side, give the lawnmower blades a gentle thrust to make them move.

Step 5: Close all the components:

After all this day long hustle, most of your technical work is done. However, closing all the components is the essential key for prolonged safety from damage. After all the parts have been lubricated and dried up, conceal them as they were taken out. Ensure the seals are tight, the crankshaft is fixed, and piston cylinders are’ t free. Close the head and fix the seat back in its place. Add new motor oil to your Lawnmower. Remove the old crude fuel. Add new fresh fuel, preferably with some anti-clogging agents mixed in. For a week on, use the mower gently and regularly so that engine gets back to its full potential.

Even if, after all these steps, the blades aren’t softening up as much as they should, it is time to call in an expert.

Related Questions:

1) Why should I use a wooden hammer or wood to strike the piston cylinders?

The combustion chambers are quite sensitive parts in terms of dimensions and sensitivities of pressure, are, and volume. A regular hammer, if used to thump the cylinder, may cause the cylinder to disorientate. At the very least, it can cause a dent in the cylinder or piston due to its rigid nature. Deformities can cause a change in the critical pressure or volume of rotating machines, which can be very dangerous.

A wooden hammer, on the other hand, is rigid and flexible at the same time. You may have observed that all denters use a wooden hammer to remove the dents too. This allows them to give a considerable power strike keeping the flexibility and geometry intact.

2) How can you tell if your lawnmower engine is seized?

To tell if a lawnmower engine is seized, you have to follow through a few steps. Start by removing out the spark plug to expose the channel to the combustion chamber. If a lawnmower with a removed spark plug still jump-starts, its valves may be worn out and hence, need replacement. However, if the engine doesn’t run and the blades are rigid and don’t turn over, it is seized. A seized lawnmower engine has locked cylinders, blades, and pistons.

3) Why removing the spark plug is necessary?

When operating on a riding lawnmower with sharp blades, precaution is a must. While cleaning, one has to clean the combustion chambers, piston cylinders, and valves. Sometimes, even the cord needs maintenance, so it has to be pulled. So, as a safety measure, it is advisable to remove the spark plug before any Lawnmower action to keep away from any harm.

Final Remarks:

For those who love their hobby of gardening, a lawnmower is the best buddy one must-have. However, after long gaps or after de-winterization, its use may pose some problems in engine activity seizing up. A seized engine doesn’t mean the machine’s death, but it sure affects its life if not addressed. Following the steps mentioned above in definite order, you can efficiently deal with this issue. It may seem huge at first glance, but following the guide will help you step by step. Even after all these steps, your Lawnmower fails to work correctly, and it is better to take it to a mechanic. Happy lawnmowing!

Lawn Mower Engine Surging – Check this easy fix first!

Lawnmower engine surging is a right pain in the Jacksie; it’s an engine that runs erratically and revs up and down by itself uncontrollably. In some cases, it may only happen under certain conditions, for example, only after the mower gets hot or only when the fuel level gets low.

So what causes the lawnmower engines to surge? The most common reason for a surging lawn mower engine is a blockage in the fuel supply, but there are other possibilities:

Often you’ll find playing around with the throttle helps or applying some choke. You are not on your own; this is a regular complaint. In this guide, we will cover the diagnosis, likely causes, and solutions.

Try the easy fix first – replacing/cleaning gapping the spark plug before attempting carburetor work. If your mower engine is a Honda or Kohler, the fix is simple. Honda and Kohler’s surging is commonly caused by a blocked idle jet see “Gas starvation” towards the end of the page.

If your surging mower is a Honda, check out the “Honda mower surging video.”

For many mowers, the fix is to replace the carburetor, and as carburetors are inexpensive, it just makes sense to swap it out and save a ton of messing around. You can check out the quality carburetors available and conveniently delivered to your door by Amazon.com.

Briggs Stratton Surging

Surging BS Classic 450, 500, or 550Some engine types are famous for surging; the Briggs Stratton 450, 500, and 550 series engines are fitted with a metal fuel tank and priming bulb-style carburetor. If you have one of these types of engines and it’s surging – You’re in the right place.

If you don’t have this type of carburetor, skip this section and jump to “Surging Test” below. These engines are fitted with a metal fuel tank and carburetor combination. The gasket sandwiched between the tank and carburetor distorts over time, allowing a vacuum leak.

The vacuum leak causes the surging; replacing the gaskets and cleaning the carburetor/tank will leave it like new, I promise. In this tutorial, we’ll remove the tank/carburetor unit, clean it and replace the gaskets. Just some basic tools are needed, but get yourself a can of carburetor cleaner; it makes the job a lot easier.

In the workshop, I use WD40 carb cleaner, and you can check out all the tools and parts I use here on the “Small engine repair tools” page.

Tools You’ll Need

Here’s a short list of tools you’ll find useful to complete the task of fixing your surging mower. These tools aren’t essential, but they do make the whole job a ton easier; you’ll need:

Fuel treatment – Every small engine owner should use gas treatment. Most people don’t know gas goes off, and gas left in small engines can cause real problems, as you already know.

Using a gas stabilizer will keep the gas in your mower and your gas can fresh for up to two years.

Carburetor gasket – If you’re fixing the BS Classic engine, then you’ll need this gasket set.

Complete carburetor – As an alternative to replacing your BS Classic carburetor gasket, replace the complete carburetor instead; it includes the replacement gasket.

Manifold – This will only be needed if you have confirmed it has failed. Note there are a few different types of manifold pipe, so be sure to check before ordering.

You can check out all these tools on this page “Carburetor Surging Repair Tools.”

This carburetor style is fitted to a few engines and is prone to gasket failure. The job of replacing is simple and will solve the surge. The process is as follows:

Remove the spark plug wire – prevents the mower from starting.

How to Fix a Riding Lawn Mower Doesn’t Crank or Click

Remove – Remove and clean the air filter and filter housing – Clean it using soapy water, and when dry, smear some engine oil over the surface of the foam. This helps trap dirt.

Remove tank bolts – They hold the fuel tank to the engine.

With fuel tank bolts removed – pull the tank unit straight out gently and remove the governor control link.

Remove the black rubber elbow crankcase breather pipe. Remove the manifold seal and keeper ring. Sometimes they will come loose and get stuck on the manifold pipe.

Remove – Remove carb screws from the carburetor and set aside.

Using a can of carburetor cleaner – clean all the ports on the surface of the fuel tank.

Empty the tank and rinse it out with fresh gas.

Pull the Siphon from the carburetor; they can be stubborn. Remove both gaskets and use carburetor cleaner to clean the siphon metal filter and all ports of the carburetor. Check the primer bulb for damage; mice like to eat them.

Spray – Spray the carburetor with carb cleaner.

Remove – Remove old gaskets and discard them.

Careful of this spring; it lives under the gaskets, and it can drop off and be tricky to find, as I know only too well.

The gasket is a two-part kit; the rubber-type gasket faces the tank. (carb fitted here for demo only)

The Siphon pushes back into the carb with a click. If you don’t hear the click, it’s not right – try again.

Refit the carburetor to the tank. Don’t over-tighten the screws, as this will distort the gasket. Fit manifold seal and keeper. Smear a small amount of oil on the seal; it helps it seat.

Clean the intake manifold. The grey tube in this shot is manifold. Inspect it for any signs of damage; they are prone to cracking. This will also cause a surge.

To fully inspect the pipe, you need to remove the pull assembly.

I would only do this if there was obvious damage to the manifold or if I had replaced the carburetor gasket and the engine was still surging.

This manifold is cracked and will cause a surge.

Before refitting the tank, fit the keeper ring and O-ring seal. Lube the seal before refitting the gas tank.

Offer the carb/tank unit up to the manifold and attach the governor link and spring. Now push the unit firmly onto the manifold. Fit both bolts.

Refit the air filter and spark plug wire. Use only fresh gas; make sure your gas can is clean. Gas older than three months is stale.

If, after fitting the gaskets, you still have a surge – Replace the Manifold.

Surging Test

As you know, gas starvation causes an inconsistent flow of fuel which in turn causes erratic running. And you also know a vacuum leak will cause erratic running, but it is a much less common cause; however, some carburetors are prone to vacuum leaks.

As engine manufacturers strive to make their engines more efficient, they have also made the carburetors more likely to clog; this has become a common issue.

To quickly diagnose which problem you have, a clogged carb or vacuum leak, follow this simple test.

You will need a helper to hold the bail lever or improvise with duct tape. CAUTION careful where you place your fingers and toes; the engine will be running, so the blade will be spinning.

Your mower will have a Manual choke, Auto choke, or a Primer bulb. Identify which type your mower has; the test is slightly different for each.

If you have a manual choke – apply half choke with the engine running.

If the engine now runs without surging – Gas starvation is the likely fault. If it runs just the same – A vacuum leak is a more likely fault.

If you have an Auto choke – Remove the air filter cover and filter – place a clean rag over the intake while the engine is running.

If the engine now runs without surging – Gas starvation is the likely fault.

If the engine runs just the same – A vacuum leak is the more likely fault.

If you have a primer bulb – you can still do the test – while the engine’s running (need a helper); give it some extra gas by pressing the bulb.

If the engine now runs without surging – Gas starvation is the likely fault.

If it runs just the same – A vacuum leak is a more likely fault.

Gas Starvation

If the test revealed gas starvation, it also showed that your problem is likely a dirty fuel jet in the carburetor, or the gas may be stale or contaminated by water.

Idle Jet Surging – Honda and Kohler use a relatively easy-to-access idle jet that clogs up and causes surging. The Kohler is easier to access than the Honda. Briggs has fitted a plastic carburetor to a range of engines which also clog up and cause surging.

All of these carburetors can be repaired by cleaning. It’s all covered in the video library. It shows you step by step how to remove, clean, refit, and adjust your carb. It’s a detailed, engine-specific guide, easy to follow, and only regular tools are needed.

Fixing this is not difficult. Sometimes you can get lucky by just draining and cleaning the gas bowl, which only takes a few minutes. I have written a complete guide to Carburetor cleaning with pictures; it includes the gas bowl clean-out, which is worth trying first.

If cleaning doesn’t work out for you, go ahead and swap out the carburetor for a new one. Check out “New lawn mower carburetors page,” here, I’ve listed good quality replacement carburetors for all the most popular engines.

Carburetors aren’t so inexpensive; messing around with them doesn’t make sense.

You might find this page helpful, too – “Carburetor repair tools” I’ve listed some really useful tools that make the job easy. Some of these tools I’ll bet you already have some.

But do try cleaning the gas bowl before removing the carburetor.

Finding a Vacuum Leak

Air that enters the combustion chamber without passing through the carburetor is un-metered. This means the fuel-to-air ratio is unbalanced and, in turn, causes erratic engine performance.

When air sneaks in like this, it causes the engine to run lean (lacks gas). A lean engine runs hot, which isn’t good for an engine, especially an air-cooled one.

Vacuum leaks usually occur because of damaged gaskets. Gaskets are sealing materials fitted between the mating surfaces of engine components. Their function is to create an airtight seal.

They are commonly made from paper, felt, cork, Teflon, neoprene, metal, and rubber. The material type is dependent upon where the gasket is to be used.

Gaskets wear out and break down, and that causes surging.

Extreme Caution – You need to be careful, the engine will need to be running, and so the blade will be spinning when running this test.

A vacuum leak check is performed with the engine running and a can of carburetor cleaner; WD40 works, too, (is there anything WD can’t do?)

Spray the cleaner around all carburetor gaskets anywhere the carburetor meets the engine. The trick is to hear an instant change in engine note; that’s the sign of a vacuum leak.

This can be challenging; you must train your ear to notice the instant change in engine note (and not the surging).

Just do a small section at a time; this will allow you to pinpoint the failure area. Jumping the gun and replacing gaskets without finding the actual leak may work out for you or leave you with the same problem after the rebuild. You’re right in thinking carburetor gaskets usually cause the problem, but other components, such as manifold pipes, can crack or become loose, causing surging.

Fixing A Vacuum Leak

If a leak is detected, replace all carburetor gaskets, and as you have the carburetor removed, go ahead and clean it. Replacement gaskets are available online; you will require the make and model numbers from the engine.

All manufacturers will have a model number printed on a sticker placed on the body or on the engine. Have a poke around; you’ll find it. Most engine manufacturers will stamp the model numbers in an accessible area. Briggs Stratton stamp their numbers on the metal engine cover.

A new carburetor comes with new inlet gaskets; I like to fit original parts where I can; they fit and are guaranteed.

If, after replacing the carburetor gaskets, the engine still surges, you’ll need to go a little further and replace the manifold intake and gasket.

It’s not a big job, and they don’t give a lot of trouble, but they do crack as they get older. I wrote a step-by-step guide showing you everything you need to know – “Briggs Manifold Replacing.”

Related Question

Honda lawn mower surging fix? To fix a surging Honda lawn mower engine, clean the carburetor, gas tank, and fuel filter. Use fresh regular gas or e10. What causes a lawnmower to run slowly? The most likely cause is a throttle linkage bent out of shape by bumping into the shrubbery or a throttle spring has detached itself.

Hey, I’m John, and I’m a Red Seal Qualified Service Technician with over twenty-five years experience.

I’ve worked on all types of mechanical equipment, from cars to grass machinery, and this site is where I share fluff-free hacks, tips, and insider know-how.

Riding lawn mower engine spins but won’t start video

Find out what to do when your riding lawn mower spins but won’t start. Once it’s spinning, the engine needs 3 things to run—fuel, spark and compression. This video helps you find out which one of those elements is missing in your engine by showing you a quick starter fluid test that can rule out several issues. Then we’ll show you how to check for problems with the fuel supply, the spark plug, ignition coil and flywheel key. Following these troubleshooting steps should help you get your riding lawn mower started so you can get back to mowing.

For additional repair help, including common symptoms and troubleshooting tips, step-by-step riding lawn mower and tractor repair guides and articles, check out our repair help section. In addition, find the riding mower parts you need to fix your mower.

Supplies you might need

• Air filter (if dirty)
• Fresh gasoline (if old)
• Fuel stabilizer
• Fuel filter (if dirty)
• Fuel line (if clogged)
• Fuel pump (if broken)
• Ignition coil (if spark plug wire is damaged or there’s no spark)
• Spark plug (if fouled or damaged)
• Spark plug wrench
• Spark plug tester
• Flywheel key (if broken)
• Flywheel puller
• Cylinder compression gauge (if all else fails)

The supplies you need depend on how far into the troubleshooting steps you go before solving the problem. Starter fluid is used in the first test, so you do need it.

Hi, Wayne here from Sears PartsDirect. Today we’re going to troubleshoot a riding lawn mower engine that spins but won’t start when the starter motor runs. Once it’s spinning, the engine needs 3 things to run—fuel, spark and compression.

Test the fuel supply

Here’s a quick test that can often eliminate 2 of those suspects right away. We’ll check to see if the engine has compression and spark by spraying a short burst of starter fluid into the engine’s cylinder. The highly combustible starter fluid will start the engine briefly if the cylinder gets spark and the right amount of compression.

In a well-ventilated area, pull off the air filter and spray a short burst of starter fluid into the cylinder through the carburetor’s air intake. Now try to start the engine.

If the engine doesn’t start at all, you can skip the next section on fuel system troubleshooting and move on to checking the ignition system.

If the engine starts briefly and then dies, you know the spark and compression are okay, leaving you with a fuel supply problem.

Troubleshoot the fuel system

A dirty carburetor is usually the culprit when the engine isn’t getting fuel. But, before you replace or rebuild the carburetor, check these basic fuel supply issues so you don’t waste your money on a part that you don’t need.

• If the air filter you just pulled off is dirty, replace it. You need a clean air filter so the right amount of air can mix with the fuel to start the engine. Here’s a video that shows how to replace the air filter.
• If you haven’t used the riding mower for several months, drain and refill the fuel tank with fresh gas. Over time, gas absorbs water and loses combustibility. In the future, if you don’t use up all the gas before storing your riding mower for several months, add fuel stabilizer to your gas tank.
• Replace the fuel filter if you haven’t changed it within the last year. A clogged fuel filter won’t allow gas to flow to the carburetor. Here’s a video that shows you how.
• Check the wire harness connection on the fuel solenoid valve. The fuel solenoid valve shuts off fuel to the carburetor to prevent backfire when you kill the engine. If the wire’s disconnected, the solenoid won’t open to allow fuel to flow to the carburetor. Reconnect the valve wire harness if you find it disconnected.
• Check the fuel line from the fuel tank to the carburetor for clogs or damage. Clear any clogs and replace the fuel line if damaged.
• If your engine has a fuel pump, replace the pump if it doesn’t move gas through the fuel line to the carburetor.

If you found no problems when checking these fuel system issues, then rebuild or replace the carburetor to restore the fuel supply to your engine. Here’s a video that shows how to replace the carburetor and one that shows how to rebuild it.

Free mower. Won’t start. Cover the air intake! Briggs engine, Craftsman mower #smallengine

Troubleshoot the ignition system

If your engine didn’t start with the help of starter fluid, check the ignition system.

First, make sure you have the spark plug wire firmly connected to the plug. Replace the ignition coil if you find damage to the spark plug wire because the wire is part of the coil. Here’s a video that shows how.

If you found no problems with the spark plug wire, pull the spark plug wire off the spark plug and remove the spark plug. Check the spark plug tip for carbon or oil deposits that could prevent the plug from sparking. Also, check for cracks in the plug’s insulator. Replace the spark plug if it’s too fouled to spark or the insulator is cracked. Here’s a video that shows how.

If the spark plug looks okay, use a spark plug tester to see if the plug gets current from the ignition coil. To test it, install the spark plug and connect the boot of the tester to the spark plug. Connect the engine’s spark plug wire to the other end of the tester. Crank the engine and see if the tester sparks.

If the tester doesn’t spark, it’s likely you need to replace the ignition coil. Here’s a video that shows how.

Check the flywheel key

If the plug sparks, that means the ignition coil is good, but the timing for the spark might be off.

Here‘s how the timing works on a riding lawn mower engine.

The flywheel magnet and ignition coil control spark timing. When the flywheel magnet passes the ignition coil, the coil generates and sends current to the spark plug, causing the spark.

The flywheel key keeps the flywheel aligned on the engine crankshaft so the magnet passes the ignition coil at the right time.

The flywheel key is a small metal rectangle that keeps the crankshaft and flywheel aligned when you tighten the flywheel bolt. To protect expensive engine components from damage, the flywheel key shears if a mower blade hits an object with enough force to make the flywheel slip out of alignment with the crankshaft. If you hit a rock or stump and the engine suddenly stops, you may have knocked off the timing by damaging or breaking the flywheel key.

A damaged flywheel key means the magnet won’t pass the ignition coil at the right time for the spark plug to ignite the fuel to start and run the engine.

If this scenario sounds familiar because you did hit an object while mowing and the engine stopped, remove the flywheel and check that key. Replace the flywheel key if you find damage. Here‘s a video that shows you how.

Check the cylinder compression

If you find no problems with the ignition system, then a compression problem could be preventing the engine from starting.

Check the oil level to see if the engine is overfilled. Drain some oil to drop it below the maximum fill level.

If the oil level is okay, pull out the spark plug and check cylinder compression using a compression gauge. This test shows whether the piston is compressing the air and fuel mixture in the cylinder.

Connect the compression gauge to the cylinder through the spark plug hole. Zero the compression gauge. Briefly turn the key to the start position so the starter motor spins the engine.

Check the compression reading. Most engines should measure over 40 psi of compression. Many engines produce more than 80 psi.

If cylinder compression is less than 40 psi, the piston isn’t compressing air inside the cylinder. Keep in mind that a low compression reading shows you that a compression problem exists, but doesn’t reveal the cause. You might need to adjust the valves or replace the piston rings. A damaged cylinder wall can also prevent the piston from compressing air inside the cylinder.

To accurately analyze a compression problem, have a service technician do a leak-down test on the engine. The technician will use an air compressor and special tools to find where the air leaks.

Once the technician finds the cause of the compression problem and fixes it, you can get back to mowing.

I hope this video helps you out today. Check out our other videos on the Sears PartsDirect YouTube channel and subscribe to see when we post new videos.