How To Turn Off A Lawn Mower

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 lawn mower? 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 an insulated pliers. Other options include: 

  • Apply Full Choke
  • Turn Off Gas Tap

Most mowers come with what's known as the dead mans 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 my easy to follow guide "How to start/stop a lawn mower". The dead mans lever doesn't give too much trouble, but if the wiring has come loose at the engine, the mower may not shut down.

Other mowers may simply have a cable operated lever to turn the mower on/off, these type 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.

Mower bail lever

Bail Lever

Releasing the bail lever kills the engine.

Mower choke lever stop start lever

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, 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.

 

Option 1

Apply full choke, this will cause the engine to get too much gas and it will likely stall. If your mower has auto choke or a primer bulb you won't be able to apply choke manually so instead remove the air filter cover and air filter.

 

Using a clean cloth, cover the mouth of the carburettor, this restricts air flow and chokes the engine. 

 

Option 2

Most lawn mowers will have a gas tap, it lives usually beside the carburettor and when turned to the off position, it kills the gas flowing to the engine.

 

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 stall.

 

Option 3

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

 

The plug wire is a push on pull off fit and are pretty easy to remove, sometimes they can be on pretty tight, so twisting while pulling helps.

 

Mower choke lever mower air filter

1 Apply Choke

Apply choke, this will cause the engine to stumble and stall eventually.

If you don't have a choke lever placing a clean cloth over the carburettor will have the same effect.

Mower gas tap Mower gas line

2 Turn Off Gas Tap

Not all mowers will have a gas tap, if you have one, it will be fitted to the gas line between the carburettor and the gas tank, or it will be part of the carburettor.

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

The engine won't stop straight away, but it will stop after about a minute.

mower blade bolts

3 Pull Plug Wire

Using an insulated pliers, grip the plug by the boot and give it a twist and a pull.

The mower will move towards you if not secured, so be careful of the toes.


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 are:

  • Maladjusted cable
  • 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 ground instead. This is exactly what happens when you switch off the mower.

 

The most common reason the mower won't shut down is because the small single ground wire has come detached or is making poor contact. The mower will run just fine without this wire, it just won't shut off. 

mower coil mower spark plug

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 gives the coil a shorter path, it does this by connecting a ground wire to the coil.

mower throttle lever Mower throttle lever Mower throttle lever

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 type set ups will have a cable that will need adjustment from time to time.

mower engine valves mower engine valves mower engine valves

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 single wire.

This as you know stops the flow of volts to the spark plug. 

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

Pictures show the flywheel brake assembly in the engine off and engine on positions.

Related Questions

How does a small engine kill switch work? The small engine kill switch sends the coil a direct path to ground. The stored voltage in the coil is then discharged, instead of firing the plug. To start the engine, the kill switch simply takes away the coil path to ground.

How do I start my lawn mower with a choke? First check the oil and make sure the gas is fresh.

  • Check gas level
  • Put choke full on
  • Pull start engine
  • When running, move choke to half
  • After 30 seconds turn choke off

Auto Technician and Writer at | Website

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