How To Turn Off a Lawn Mower – Quick, safe solutions. Lawn mower kill switch

12.06.2023 Beanrad lawn, mower, quick, turn

[Don’t Panic!] Easily Fix a Push Mower That Won’t Turn Off

It’s a slightly nerve racking ordeal to be pushing your trusty mower around your lawn and need to stop for whatever reason, only to find that the engine and blades refuse to shut off. This can be very dangerous, especially if there is a reason to need to have the blades stop instantly due to an emergency!

Let’s not waste anymore time with the intro and get right into what you need to do to stop the engine for the time being, and how to fix the problem going forward.

If you’re here about a riding mower (lawn tractor), check out my article here to help you with that. This article will cover push mowers.

This article will teach you what to do in the immediate moment to get your mower to stop, what to check to fix it in the future, and that I’ll cover why and how a mower turns off if you want a more detailed explanation to understand the mechanics behind it.

How to Emergency Stop a Push Mower that Won’t Turn Off

The safest and most reliable way to stop a push mower that won’t turn off after releasing the bail control arm is to take a pair of insulated pliers (the handles are covered with rubber) and pull the ignition coil boot away from the spark plug. This will stop combustion in the engine and stop your blades and engine.

We use insulated pliers just in case there’s a crack in the ignition coil wire so that it doesn’t try to direct the voltage for the spark through the pliers and into our bodies. To stop a push mower that won’t turn off, remove the boot from the spark plug with a set of insulated pliers.

If you’ve ever served as the ground for a spark plug and pulled the recoil cord, you’ll know what I’m talking about. If you haven’t, then trust me — use insulated tools when dealing with any electrical current.

How to Fix a Push Mower That Won’t Turn Off

The following sections will cover why we’re going to the following steps in order to fix the lawnmower. This section will only cover what you might need to do to get things fixed.

Before doing any work on your lawn mower, please remove the spark plug boot for safety purposes.

Situation #1 (Most Likely):

If you let go of the bail control arm (the little bar that you squeeze to the handle when you’re using the mower — see pic above) and you hear the engine running rougher but not turning off, then you’ve got a brake assembly that is working properly against the flywheel but there is a broken connection between the brake assembly and the kill switch.

In this case, you will likely need to remove the covers and shrouds up top unless you can clearly see and access your brake assembly without removing anything. You need to be able to see and access what’s in the picture below. In this case, the bail is being squeezed to the handle of the mower. The pad is lifted back from the flywheel (allowing the blades, camshaft in the engine, and the flywheel to turn), and the grounding arm of the brake assembly moves toward the flywheel and away from the kill switch. Once the connection between the grounding arm and the kill switch is broken, then the spark plug will fire. Everything pivots on the bolt where the brake assembly label points. If you let go of the bail and the brake pad engages but there is too much dirt between the grounding arm and kill switch or if they got bent apart from each other, then the mower will continue to run but run rough since the brake is now engaged.

When you squeeze the bail control arm, you are lifting the brake pad off of the flywheel and also moving a grounding arm away from the kill switch arm.

When you release the bail control arm, the brake pad should be pushing against the flywheel and the grounding arm should make clean contact with the kill switch.

In this particular case, connection is not being made.

If you see excess dirt and debris, remove it with an old toothbrush, a wire brush or whatever else you might need to clean up the connection. If something is stopping the flow of electricity between the grounding arm of the brake assembly and the kill switch, then the push mower will keep running.

If you see that they aren’t contacting each other at all, then you can either slightly bend the grounding arm up with a pair of pliers until it makes contact, or you can slightly bend the kill switch down until contact is made.

I prefer to bend the grounding arm up since the kill switch is more fragile.

Situation 2 (Least Likely):

If you release the bail control arm and the engine doesn’t change speed and continues to run, then you likely have a brake assembly that got get stuck in the open position due to rust or corrosion and won’t release when you let go of the bar.

For this step, you may or may not need to remove the top covers from your particular lawn mower in order to access the brake assembly and kill switch. You must be able to see and access what is in the picture above.

Go ahead and spray some lubricant or squirt a little oil on the area where the brake assembly pivots and work the assembly back in forth with your hands to lubricate things.

If you’re ambitious, you can easily remove the brake assembly and clean everything with a wire brush, lubricate the moving parts, and put it quickly back together.

Do not spray the brake pad that makes contact with the flywheel with lubricant. This would defeat the purpose of the brake.

Verify that the brake pad now makes contact with the flywheel and that the kill switch makes contact with the grounding arm on the brake assembly.

Why Won’t My Push Mower Turn Off

As a general rule, a push mower will not turn off if there is a disrupted connection between the kill switch and the grounding arm on the brake assembly. This can be caused due to dirt and corrosion, or if the switch and grounding arm became bent away from each other.

Cleaning the connection with a wire brush and bending the grounding arm to make contact with the switch will solve the problem.

How Does a Push Mower Turn Off

A push mower will turn off when the bail control arm near the handle is released. This will allow the brake pad to make contact with the flywheel which will slow the blades, and it will also allow the grounding arm on the brake assembly to make contact with the engine’s kill switch and stop the spark plug from working.

That’s the 10,000 foot view of what happens.

If you’ve read this far, you might be wondering just what makes it all work. Why does that bail arm lever up top stop the engine.

When you squeeze the bail arm lever against the handle, you remove the brake from the flywheel and allow it (along with the blades and crankshaft in the engine) to spin freely. You also move the grounding arm of the brake assembly away from the kill switch.

How the kill switch works is that it’s just a small, rudimentary piece of metal with two arms that is isolated electrically from the motor. It usually sits on the back of the engine and is always near the brake assembly.

The kill switch has a path for the ignition coil to ground itself against the brake assembly (and therefore the frame of the push mower) when the bail arm is released and therefore no electricity will be directed to the spark plug. When the bail arm is squeezed, contact between the kill switch and the brake assembly is broken, the ignition coil is no longer grounded, and the spark plug will be energized with each rotation of the flywheel.

One one arm of the kill switch is a small wire that is jammed in place. If you follow this wire to the front, you’ll see that it leads to the ignition coil. The ignition coil is what sends an electrical impulse to the spark plug every time the magnet on the flywheel passes it during operation.

So, with the bail arm lever up top squeezed against the handle, the brake is lifted and the flywheel can spin and allow the ignition coil to send electricity to the spark plug so that combustion can occur in the engine. The bail arm has been released. When compared to the picture above, you can see that the brake pad is now pressing against the flywheel, and the grounding arm has pivoted back and made contact with the kill switch. Now that the electrons have an easy path to ground, the spark plug will not receive any electricity and will cease firing.

Remember that with this basic direct current electrical pulse that’s occurring, the electricity is simply a bunch of agitated, negatively-charged electrons that are all being pushed in the same direction and want to find a positively charged place to go — or at least one that’s less negatively charged as they are.

Before this pulse of current is allowed to go to the spark plug to ground itself out and make a spark, it has the option to first ground itself out (find its positively charged place, aka the frame of the mower) on the kill switch.

If the kill switch is making contact with the grounding arm of the brake assembly (bail arm control released), which makes contact with the frame of the mower, then the pulse will always take this path since it is the easiest for it to follow.

If there is a dirty connection or a bend switch or grounding arm, then the pulse cannot find its positive place there and will proceed instead to the spark plug.

When it arrives at the spark plug, the current is forced up the center of the spark plug and will cross the gap to the probe on the other side. When the electrons cross, the result is a spark, and they do so because the probe on the opposite end of the spark plug makes connection with the threads of the spark plug which, of course, make direct contact with the engine itself when the spark plug is screwed in. A small, blue spark can be seen. When the threads of the spark plug are grounded against the frame of the generator, then the agitated, negatively charged electrons will be pushed up the center of the spark plug and will arc across to the bent-over probe on the top of the spark plug that touches the threads (which are grounded). The electrons have now moved to a more “positively-charged” environment.

Robert lives in central Michigan and enjoys running, woodworking, and fixing up small engines.

How To Turn Off a Lawn Mower – Quick, safe solutions

When a mower is working correctly, releasing the bail lever turns off the mower. If your mower doesn’t have a bail lever, then the throttle lever doubles as the on-off control. However, a mower that just won’t turn off is actually quite common, the solution is usually simple, but first, we’ll need to kill the engine.

So, how to turn off a lawnmower? The fastest way to turn off a mower that won’t stop is to remove the spark plug wire. The wire carries voltage, so you’ll need insulated pliers.

Other options include:

Most mowers come with what’s known as the dead man’s lever, you may know it as the Bail lever and as you know you must hold it to start the mower and release it to shut it down. Check out “How to start / stop a lawn mower”. The dead man’s lever doesn’t give much trouble, but if the wiring has come loose at the engine, the mower may not shut down.

Other mowers may simply employ a cable-operated lever to turn the mower on/off. These types of controls are usually fitted to mowers that also have a blade engage control lever. Anyway, I’ll show you three options to shut off your mower, and then we’ll take a look at what could be causing the problem.

Bail Lever – Releasing the bail lever kills the engine.

Stop/Start Lever – Move the lever to stop position kills the engine.

Shut Down The Engine

You have three options to shut down a mower with a faulty on/off switch. The fastest way by far is to pull the plug wire, but wow, not so fast, you’ll need a pair of insulated pliers.

The other options work for most mowers, but they may flood the engine with gas and so the engine might not restart for 30 minutes or so until it dry’s out, but it won’t hurt the engine any.

Option 1

Choke – Apply full choke, this will cause the engine to get too much gas and it will likely stall.

If your mower has an auto choke or a primer bulb you won’t be able to apply the choke manually so instead remove the air filter cover and air filter.

Using a clean cloth, cover the mouth of the carburetor, this restricts airflow and chokes the engine.

Option 2

Gas Tap – Most lawn mowers will have a gas tap, it lives usually beside the carburetor and when turned to the off position, kills the gas flowing to the engine. Need help finding your gas tap, click here.

Turning the gas off won’t take effect right away, it may take a minute or two before the engine starts to stumble and eventually stalls.

If you don’t have a tap, you can stop fuel flowing to the carburetor by pinching the gas line with pliers or vice grips.

Option 3

Plug Wire – The plug wire carries voltage and will shock if you just grab it, it’s not enough to kill you but if you have a heart complaint it could. It’s quite safe to pull the plug wire while using plastic-handled pliers.

The plug wire is a push-on pull-off fit and is pretty easy to remove, sometimes, however, they can be on pretty tight, so twisting while pulling helps. Be mindful, the mower will move towards you if not secured, you don’t want your toes going under the deck.

Be Smart about this, move the mower so that the front wheels face a wall, then yank on the wire.

Why Won’t The Engine Turn Off?

Faulty wiring is the common reason a mower won’t shut down, the wiring as you expect is simple. Banging into fences and cutting under hedges and shrubs can cause small components to come loose.

Other common causes include:

Loose wiring
Cable out of adjustment
Faulty flywheel brake
Faulty on / off switch

How’s it Work?

The coil and flywheel create the energy that the plug needs to fire. At its simplest – the positive charge travels from the coil through the plug wire to the spark plug. The positive energy is always looking for the shortest path to negative/ground (engine casing), and since its only option is to jump the spark plug gap, it does so and creates a spark in the process.

But if you offer the coil a more direct path to negative/ground it will bypass the spark plug and send the voltage to the ground instead. This is exactly what happens when you switch off the mower. The most common reason the mower won’t shut down – the small single ground wire has become detached or is making poor contact. The mower will run just fine without this wire, it just won’t shut off.

Look for any obvious signs of loose wiring, you might find this post helpful “Toro won’t shut off”.

Spark – Voltage passes down the plug wire through the plug and jumps the gap causing the spark. If the coil is given a more direct path, it won’t travel down the coil wire to the plug.

Turning the mower off offers the coil a shorter path, it does this by connecting a ground wire to the coil.

Lever On/Off Switch – The Bail lever is a common way to turn off a mower engine. It has 4 components bail lever, cable, brake assembly, and on/off switch.

Other mowers may have a throttle lever and stop-start unit combined. These types of setups will have a cable that will need adjustment from time to time.

Brake Assembly – When the bail lever is released or throttle lever set to stop, depending on which type you have, a brake is pressed against the flywheel and a direct ground path is given to the coil through a switch and or single wire.

This, as you know, stops the flow of volts to the spark plug, if it’s disconnected it won’t divert voltage and so your engine won’t turn off.

The black switch seen here with a single wire push-on the connector is the on/off switch.

Rouge River Workshop

Queen Anne Table Legs? We Don’t Need No Stinking Queen Anne Table Legs!

Thursday, August 7, 2014

Tecumseh TVS90 Kill Switch Operation

The kill switch on a Tecumseh TVS90 lawnmower engine resides under the engine’s flywheel, where it works in conjunction with the engine brake. A closed kill switch grounds a point in the ignition system, killing engine operation. Here’s a view of the switch in its closed/off/kill position. (I’ve whitened the switch’s ‘pigtail’ contact to make it easier to see.)

And here’s a view of the switch in its open/on/run position.

The switch itself is rugged and adjustment-free; its only real enemy is rust. ( on that later.) Following are the likely failure modes/mechanisms:

a) Engine Won’t Start.- No Spark

A stretched/binding control cable can cause this when the cable develops insufficient travel to open the switch. The best solution is replacement of the control cable. In a pinch, it’s possible to ‘adjust’ the switch to accommodate the impaired control cable by bending the switch’s wire ‘pigtail’ contact. That’s not a method that I recommend, but I have done it and gotten away with it.

b) Engine Won’t Stop When Bail Is Released.- Binding Control Cable

This is an unlikely failure mode because of the switch’s design.- the switch doesn’t need much control cable travel in order to close. However, it is a possible failure. The only practical solution is replacement of the control cable; there’s no good work-around for a cable that’s binding that badly.

c) Engine Won’t Stop When Bail Is Released.- Rusty Switch Contacts

I’ve actually seen this failure happen.- a kill switch with contacts so rusty that it couldn’t make, even though it would physically ‘close’. The solution was to scrape/file the mating switch contact surfaces. That got the switch working again.

Toro Timemaster Won’t Shut Off (Easy Fix!)

What a pain in the jacksie! Most mowers have the opposite problem, I don’t know which is worse. Anyway if you want to shut your mower off quickly, pull the plug wire, but you’ll need insulated pliers. (Insulated pliers is any plastic handled pliers)

So what’s wrong with a Toro Timemaster that won’t shut off? The most common reason a Toro Timemaster won’t shut off is loose wiring behind the push-off button switch.

I’m a mower mechanic and I see this problem with Toro Timemaster a lot. I love Toro mowers, they build great machines. This is a minor problem and you can easily fix it right now. In this guide, I’ll show you all you need to know, including shutting your Toro off safely.

Shut Off a Toro Safely

The fastest way to shut off that Toro is to pull the plug wire. It’s safe to remove the plug wire, but – You must use insulated pliers. Otherwise, the coil will give you a jolt. An insulated plier is any plier with plastic handle sleeves. Alternatively, see below re-checking the push button wiring.

Insulated Pliers – Any pliers with plastic handles. Pull the plug wire, by twisting and pulling.

Fixing a Toro That Won’t Shut Off

Now that the engine is off we can get to diagnosing the root cause and fixing it. While I see this problem many times in a season, it is possible that the cause lies not with a loose wire at the off switch, but elsewhere. No matter, we’ll cover 3 other possible causes in this guide too.

I don’t cover how the kill switch system works in this guide as I’ve covered it in this guide “How to turn off a mower”. But first, let’s look at the most common cause – Loose wiring at the push button off switch.

Loose Wiring At The Push Button Off Switch

The push-button is as you know located on the handlebar. The button is a simple two-wire on/off switch.

The Fault – One of the push button push-fit wiring connectors simply comes loose and falls off.

The Fix – Reconnecting solves the issue. However, if the wiring is broken or loose it will need to be repaired and we cover that a little later. First, let’s check for loose wiring.

Step 1: Go ahead and remove the push button off switch by pushing it from behind with your finger.

Step 2: With the switch removed examine the wiring. This switch hasn’t just come loose, its terminal has come away. I’ll need to replace it. I cover that a little next.

Loose Wiring Repairs

Fit new connector, you’ll find all these tools in the “Small engine repair tools page”.

Faulty Push Button “Off” Switch

The next most common cause is a faulty push button switch. They’re usually pretty durable, but moisture is a switch killer.

The Fault – All-weather plastic shield cracks and corrodes the contact points.

The Fix – Replace the switch.

Step 1: Check the shielding, if the flexible plastic cover is cracked or worn, it’s a good indicator the switch is water damaged, but we’ll need to test it to be certain.

Step 2: To test the switch we’ll need a Voltmeter set to ohm’s as we’ll check for continuity between the 2 switch terminals.

A good switch shows continuity, but only when pressed. With your voltmeter set to ohm’s, check continuity. If the reading doesn’t change (stays at 1) when the button is pressed, the switch is faulty.

Check out “Small engine repair tools” page to see my recommended voltmeter.

Disconnected Engine Side Wiring

The next most common cause is a disconnected engine side wiring. The wiring harness is connected engine side at three points.

The Fault – Cutting under fencing or heavy shrubbery can catch and break or disconnect the wiring.

The Fix – Reconnect any disconnect wiring.

Step 1: Check all three wiring harness points as per the pictures below.

Step 2: Reconnect wiring or repair if necessary.

Broken Wiring Harness

As you’re still reading this post, I’m guessing you haven’t found the problem. This is the last likely issue.

The Fault – Broken wire in the wiring harness.

The Fix – Find and repair the break.

Step 1: Check for obvious signs of wiring damage. Common areas are where the wires bend and turn sharply. Mice and other wildlife like to eat wiring.

Step 2: Using a voltmeter check for continuity in each of the wires. A jumper wire may be needed to connect the voltmeter. As before, no change in the reading indicates a break in that wire. You’ll need to chase the wiring and repair it.

Faulty Coil Circuit

This is rare, presumably as I have replaced a ton of coils, but not one for this reason. So in the interest of having a complete list of all possible causes, I’ve included it.

The Fault – Broken internal grounding wire circuit.

The Fix – Replace the coil.

Step 1: Remove and check the ground circuit of the coil.

Step 2: Replace the coil. I cover replacing the coil in this video.

JUSOF.COM