This is a problem that usually arises in the spring, and for most the fix is really simple. You’ve come to the right place, and you’ll be cutting grass shortly.
So what’s the problem with a riding mower that won’t start just clicks? The most common reason for a clicking sound on a riding mower when you turn the key is a flat battery. Other possible reasons include:
- Faulty Battery
- Dirty / Loose Battery Connection
- Faulty Solenoid
- Binding Starter Motor
- Excessive Valve Lash
- Hydro-locked Engine
- Faulty Ignition Switch
- Faulty Control Module
- Faulty Starter
- Engine Seized
Yes, it’s a long list, but you won’t have to check all of them, I’ll bet your problem is one of the first three, I have listed the likely causes in order of commonality.
If your mower won’t crank and makes no click sound – Check out “Lawn Tractor Won’t Start”.
- Bad Battery Connections
- Loose Connections
- Dirty Connections
- Cleaning Connections
- Flat / Faulty Battery
- Jump Starting
- Battery Testing
- Buying a Battery
- Battery Charging
- Faulty Solenoid
- Where's the Solenoid?
- Solenoid Test
- Binding Starter Motor
- Excessive Valve Lash
- Fuel Valve Solenoid
- Faulty Ignition Switch
- Faulty Control Module
- Faulty Starter Motor
- Internal Engine Damage
- Related Questions
Bad Battery Connections
Bad battery connections are very common, and by bad I mean the power is not passing from the battery to the cables because the battery connections are loose, dirty, or damaged.
Battery cables become loose because lawn tractors vibrate a lot, this is why it’s a good idea to service your mower at the start of every season, no matter how well she runs.
Dirty connections are usually caused by the weeping of battery acid at the battery poles. The acid then crystallizes causing high resistance, it looks like a white chalky build-up on the connectors.
To clean the connections, add a couple of spoons of baking soda and a small amount of water, pour this onto the build-up of acid on the connections and battery poles.
The soda neutralizes and removes the acid, you’ll need gloves and protective eyewear. After removing the acid, go ahead and remove the connectors and give them a good cleaning with a wire brush or sandpaper.
If you have some petroleum jelly, a small coat will prevent a future build-up.
Connector – Mower blades and engines cause a lot of vibration, bolts come loose from time to time.
Check that both connections, positive (RED + ) and negative (BLACK – ) are clean and tight.
Cables – Check the cables for damage, corrosion, mice find them irresistible.
Flat / Faulty Battery
A flat battery is a real pain in the ass. I know what it’s like, you just want to cut the grass, right? The fastest way to solve this problem is to jump-start the mower.
Leaking Battery – Check your battery for leaks before attempting to jump-start. If it leaks and it’s a sealed battery, replace it.
However, it’s usually only wet batteries that leak, so best to check your electrolyte level and top up if necessary. As you know acid will burn the skin and eyes, so, you know, gloves, etc.
If the acid build-up is excessive, your battery may be on its last legs, so don’t be surprised if it has failed or does so soon.
But if the leaking is excessive, don’t jump-start, replace it. Batteries are easy to fit, just be sure the battery is the correct size and the poles are in the proper places.
You’ll need jump leads and any 12-volt vehicle. Most cars, trucks, and even Hybrids have a regular 12-volt battery fitted somewhere. Sometimes finding it is the hardest part. If you’re unsure of the voltage, when you find the battery, a sticker on the casing will indicate 12v.
Of course, your battery might just be faulty, jump-starting will probably get you rolling but the problem will still be there. You can test using a voltmeter test tool, which I’ve listed here on the “Small engine repair tools” page.
To jump-start – begin by connecting the positive red (+) of the mower to the red (+) of the car.
Now connect the negative black (-) on the car to a ground (GRD) source on the mower. (Any bare metal will work)
Connect – If you are not familiar with jump-starting, you’ll find a complete guide here, “Jump starting riding mower”. Add the cables in sequence 1, 2, 3, and 4, start the mower, and while idling remove jumper cables in reverse order 4, 3, 2, and 1.
You can check the battery and alternator using a voltmeter. Batteries don’t like sitting idle, they were designed to be charged and discharged continuously. A battery that gets fully discharged will sometimes not come back to life.
Use a voltmeter to check the battery voltage, simply connect red to positive and black to negative. I have listed a voltmeter on the “Small engine repair tools page”.
Test – Check battery voltage using voltmeter – attach a voltmeter to the battery and set it to 20 volts.
If you have a reading above 12.5 volts – go ahead and attempt to start the mower, watch the voltage, a reading below 8 volts is a bad battery and needs to be replaced.
Buying a Battery
When buying batteries – wet batteries will not ship with acid. The acid will need to be purchased and the battery will need to be filled and then charged, it’s a lot of work.
I would buy a gel battery or a maintenance-free sealed battery, these can be shipped and are fully charged and ready to roll. Check out quality common ride-on mower batteries on the Amazon link below.Amazon Ride-on Mower Battery
To keep your battery in top condition over winter, you’ll need a battery charger. I recommend a trickle/smart charger, they’re simple to use, pop on the color-coded crocodile clips, and plug it in, that’s it. Forget it till next spring, then simply turn the key and mow.
I’ve listed a good-quality smart charger that won’t break the bank on the “Small engine repair tools” page.
Batteries work best and last longer when their state of charge is maintained, off-season charging is always advised. Check out “Mower winter storage”.
Charge – Always disconnect the battery before charging. Simply connect red to red, black to black, and plug in the charger. The length of time on charge will depend on how low the battery is and the amp rating of the charger. Usually, 2-3 hours cooking time.
The solenoid is a large relay of sorts. When you turn the key to start your mower, a 12 volt supply from the ignition switch to the solenoid activates it. The solenoid’s job is to connect the battery to the starter motor and crank over the engine for as long as you hold the key.
The click sound is the solenoid trying to work by pulling in the armature, they fail regularly and I replace lots of them.
However the click sound can also be made for a few other less common reasons and without fully diagnosing, you may find replacing the solenoid doesn’t solve the problem.
Hey, if you are feeling lucky and you don’t want to do the diagnosing part, I understand. So, if your battery is full and the cables are tight, go ahead and replace the starter solenoid. They’re cheap and easy to fit.
Check out, “Mower solenoid repair tools” it lists useful tools and parts that will help you nail the repair.
Solenoid – Solenoids are a universal fit, they give lots of trouble.
On the upside, they’re easy to fit and cheap to buy.
Where’s the Solenoid?
Often just finding the starter solenoid can be challenging, I sometimes think that they hide them for fun. If you don’t find it under the hood, try under the rear wheel, behind the gas tank, or under the seat.
The easiest way – follow the red battery cable from the battery. On some engines, the starter and solenoid will be one unit (Kawasaki and Honda engines).
Where? – Husqvarna, craftsman-like to hide theirs under the rear wheel fender or under the dash beside the steering column.
However, most solenoids will be easy to locate. Fitting is easy, but do disconnect the mower battery first.
Remove – The first step in testing the solenoid – remove the spark plug.
If when removing the spark plug, gas pours from the spark plug hole – move on and check “Carburetor troubleshooting”.
Test – Turn the key, if the clicking sound persists – Go ahead and replace the solenoid.
If on the other hand, the engine cranks over, move on and check for excessive valve lash.
Tight – Check the solenoid terminals, all wiring should be secure and free from corrosion.
Binding Starter Motor
The gear head of the starter motor can bind against the flywheel, this locks the engine and starter motor together. So when you hit the key all you hear is the click sound.
Testing for this condition is a matter of turning the engine by hand anti-clockwise. Some engines will have a cover over the flywheel, if so, try turning the crankshaft with ratchet and socket, from the underside of the engine.
If turning the motor anti-clockwise frees it up – you found your problem, the starter motor is binding. Usually, a spray of wd40 on the starter gear head will fix it. If you are lucky you can get the straw of the WD40 directed at the gear head without removing any covers.
Starters can bind for other reasons – worn bearings, worn gear head, misaligned or loose starter motor.
Binding – Starters can bind against the flywheel. To fix it – spray the starter gear with wd40 and retest. If it continues to bind, replace the gear head or complete the starter motor.
Turning the engine anti-clockwise by hand will unlock it.
Excessive Valve Lash
Engines have valves that open and close in sequence. The inlet valve allows fuel/air mixture in. It then closes and seals the combustion chamber. After the power stroke, the exhaust valve opens and allows spent gases out.
What’s Excessive Lash?
It’s a precise gap between the valve tip and the rocker arm. As the engine wears this gap gets bigger and will need to be adjusted. The inlet and exhaust valve lash will usually be different specs.
When valve lash is set correctly – you crank over the engine, the valves open, and release cylinder pressure. This allows the engine to crank over at sufficient speed, in order to create a spark strong enough to start up the engine.
When valve lash is out of spec, the valve is late opening which means pressure in the cylinder is too great for the starter to overcome, that’s when you hear the click sound.
Check out “Valve lash adjusting” it’s for a walk-behind mower, but the process is identical. Adjusting lash isn’t difficult but will require an inexpensive tool called a feeler gauge. You’ll find a link to a good feeler gauge set on the “Small engine repair tools” page.
Test – If you can, place your hands on the flywheel screen – try turning the engine clockwise.
If you’re unable, it’s likely you have excessive valve lash. Lash should be checked every season.
Lash – Adjusting valve lash requires an inexpensive tool called a feeler gauge.
A carburetor fuel supply usually consists of a fuel bowl, float, and needle. The float is as its name suggests; a float, attached to it is a needle, with a rubber tip.
The function of the float is to lift the needle as the fuel level rises in the fuel bowl. When the fuel bowl is full, the needle will be pushed against the fuel feed port, sealing it.
Hydro-locking – Worn carburetor float needle seals have a habit of leaking gas into the cylinder and when the cylinder is full of gas, the piston can’t move, this is known as hydro-locking. Because the piston can’t move, the engine will often make the clicking sound as you try to start the engine.
Removing the spark plug and turning over the engine will release the gas, but the carburetor float valve and the engine oil will need to be replaced.
Other signs that your carburetor needle seal leaks are: overfull oil level; white smoke from the muffler; oil leaking from the muffler; gas dripping from carburetor; a strong smell of gas in the garage.
Fuel Valve Solenoid
Newer model carburetors have a fuel solenoid fitted to the bottom of the fuel bowl, its function is to stop the fuel supply when you shut the engine off. So if you have this newer type of carburetor fitted, it’s not likely you will have a hydro-locking condition.
Leaking Carburetor Valve Seal
Failure commonly occurs in the older type carburetor when the rubber needle seal wears. This results in fuel continuing to fill the carburetor and eventually making its way into the cylinder and crankcase.
Gas in the Oil
If you have gas in the oil, don’t run the engine, the diluted oil offers little protection to internal components. First fix the issue by replacing the carburetor and then change the oil.
Check Oil – Too much oil is a sign that your carburetor needle seal is leaking unless of course, you overfilled the oil yourself.
Needle – The needle wears over time, they turn pink when worn. The fix – replace the seal or the complete carburetor. Using your manual fuel valve will prevent future problems.
Faulty Ignition Switch
A faulty ignition switch can cause all kinds of problems, the click sound can be caused by a bad connection in or at the back of the switch.
Try the Wiggle Test
When turning the key, wiggle the wiring at the back of the ignition switch and see if it makes a difference. It will very often show you where the fault is. Wiring pinouts are specific to each manufacturer.
Wiggle – Try wiggling the wires at the back of the ignition switch while attempting to start the engine, you may need a helper.
Often wires simply come loose but do check them for corrosion.
Faulty Control Module
Control Modules are not fitted to all mowers. The function of the control module is to receive a start request from the ignition switch, and to output a 12 volt supply to the starter solenoid, but only if all safety sensors are in the correct position.
Control Module Test
Control modules do fail and also suffer from loose connectors. Try the wiggle test on the connectors and check for obvious signs of water/corrosion damage. The control module will often live behind the dashboard in a plastic box about the size of a mobile phone.
Wiggle – Like the ignition switch, wires come loose, have a helper attempt to start the engine while you wiggle the wiring connectors.
Check also for damage, water, or scorch marks on the panel itself.
Faulty Starter Motor
A faulty starter can fail electrically, mechanically, or both. Electrically – the copper winding can break; brushes can break or wear out. Mechanically – bearings top and bottom can wear, and the gear head can wear. These issues can cause the starter to bind, so all you hear is the click sound.
Testing the Starter
Checking the starter motor is easy, connect a 12 volt supply direct from the mower battery (+) to the supply wire at the starter. An even easier way is to cross the starter solenoid as per the guide below.
If you find your starter has failed, removing and fitting a new one is simple. The starter motor for Briggs and Stratton offers a good quality starter. Be mindful that B&S has two types of starter – plastic gear head or metal, check before ordering.
Starter – Some starters will have a solenoid and starter motor combined in one unit.
To test, use a jumper lead to bring power from the positive (+) of the battery. to the positive post of the starter. If the engine doesn’t crank – Replace the starter.
Common – Most mowers will have the starter and solenoid separate.
Solenoids are fitted to the body usually under the hood.
Test – Cross a metal screwdriver from one connection to the other, as per the picture.
There will be arcing (sparking) as the screwdriver contacts the poles.
RISK OF FIRE – Keep clear of gas
CAUTION THE ENGINE MAY TURN OVER – Place mower in the park with the parking brake applied and blade off.
If the engine won’t crank over – your starter is faulty, replace.
Internal Engine Damage
If you’re still reading, I fear the worst has happened. It’s unusual for mower engines to fail completely. They’re generally well-built robust units. I have seen failures like con rod breaking out through the engine casing; the main bearing seizing; con rod bending; cylinder head failures.
Some of these faults can be repaired but most are uneconomic to repair.
On the upside, if you have a total failure, a complete engine fully built with a guarantee is available and fitting involves 4 bolts, 2 electrical connectors, fuel line, throttle cable, and crank pulley.
B&S and Kohler engines are of great quality and ready to go. The completed job will take less than two hours. Be mindful all engines are shipped without oil.
Failure – Total failure doesn’t happen often.
A hard life, low/poor quality oil without doubt increase the chances.
Can you jump-start a mower? A flat or bad battery is a more common fault than a starter. Try jump-starting, if your mower starts, the battery needs attention. If jump starting doesn’t work, investigate a faulty solenoid or starter.
Can a bad alternator ruin a battery? A bad alternator can ruin a battery. Alternators have two main components. A voltage regulator that monitors and controls battery charging and the alternator whose job it is to create voltage. Common problems include a faulty regulator which damages the battery and alternator diode failure which drains the battery.