The sun’s out. The drinks are cold. The morning is early and the lawn mower is ready.
Except when you try to get things going, your mower engine cranks but doesn’t start.
It happens to the best of us, especially if it’s the first time you’re bringing out the mower for the season.
Common reasons for a lawn mower turning over but not starting include:
- Low fuel
- Old gas
- Dead battery
- Clogged carburetor
- Blocked or damaged fuel line
- Old or dirty spark plug
- Broken or dirty air filter
- Blocked gas cap
To find the cause, you’ll need to get up close and personal with your reliable lawn care buddy. Finding the issue means you can fix it – or get professional help, ASAP!
Before Checking Your Lawn Mower
Before you start tinkering, make sure the mower is shut off and the lawn mower engine has fully cooled. Unplug the machine or remove the battery if applicable.
Wear proper gloves and eye protection, and work in a well-ventilated area. Keep some old towels or containers handy, to hold any parts you take out.
For push mowers, remove the spark plug and disconnect the wires to prevent accidental starts.
You can try cranking the engine a few times after removing the spark plug, to remove any fluids in the cylinder.
Reinsert the plug and see if the engine starts – if it doesn’t, there’s an underlying cause you need to identify.
NOTE: If your lawn mower starts then dies, that’s a wholly different problem!
Why is My Mower Cranking But Not Starting?
If you’re trying to start your mower – whether via key or pull cord – you might hear it crank but the mower won’t start.
A lawn mower turning over but not starting usually happens after it’s been in storage for a long time. The usual reasons include low fuel, old fuel, or dirty components.
If you’ve checked for all the listed issues and your mower still cranks but won’t start, some less common reasons could be faulty valves, a choke fault, or malfunctioning gears.
These issues are best left to professionals to address, so bring your machine to a repair shop or contact the manufacturer.
1. Low fuel
This is one of the more common causes of a lawn mower that cranks without starting, and it’s easy to fix!
Maybe you forgot to refill the tank after the last mowing session, or maybe the mower was improperly stored and some of the gas evaporated.
Check if there’s enough gas in the tank – there’s usually a minimum level needed for the engine to get going.
HOW TO FIX IT:
Empty the gas tank and refill it with fresh gas!
It’s best to take out the old fuel and replace it instead of adding to the existing fuel, especially if you’re not sure how old the gas is.
Poorly-mixed or bad fuel can lead to your lawn mower backfiring.
2. Old gas
If you’ve had the mower in storage for a long time (like over winter), old gas may be the culprit here.
Expired or stale gas doesn’t ignite properly, so your mower might turn over but not start.
Signs of bad fuel include:
- A sour, strong smell
- A dark or unusual colour
- Floating particles or residue
If your mower got wet, water may have entered the engine system and contaminated the fuel. Check the fuel for bubbles – that’s usually a sign of water contamination.
It’s also possible the fuel evaporated and left a gummy residue inside the tank, fuel lines, or even carburetor. That restricts the flow of fuel and prevents starting.
HOW TO FIX IT:
You’ll need to empty all the old gas and refill with fresh fuel! You can also mix in fuel stabiliser to minimise the risk of engine clogging.
Take the opportunity to clean your lawn mower as well, especially if there’s residue from stale or evaporated fuel.
Remember: never introduce water or moisture into the fuel tank. You can use a light solvent or take it to a professional mechanic, especially for a riding mower.
3. Dead battery
Your riding lawn mower or battery mower might have lost juice, especially if it’s been in storage for a long time.
If you have a multimeter, you can check to see if the battery has adequate voltage. Additionally, look out for any damage like cracks or leaks.
HOW TO FIX IT:
Consult your owner’s manual for instructions on how to recharge your mower’s battery.
You can also take it to a professional mechanic to get the battery jump-started – or, if it’s damaged, replaced.
4. Clogged carburetor
If the carburetor is clogged or malfunctioning, then your mower might turn over but not start due to failed ignition.
Other signs of a dirty carb include:
- Black smoke
- Lawn mower overheating
- Poor or inconsistent mower performance
Some common causes of carburetor problems are stale fuel, a dirty air filter, or overuse. Other times, the mower’s vibrations can jolt the carburetor loose.
HOW TO FIX IT:
You’ll need to check the carburetor and see if it’s dirty or damaged.
Refer to your owner’s manual for instructions on where to find the carb. For push and self-propelled mowers, it’s usually by the air filter.
You can clean a mower carburetor with compressed air and carb cleaner. Do not introduce any water, which could contaminate the fuel or corrode metal parts.
Locating the carb on a riding mower can be tricky, so you’re better off taking it to a repair shop.
5. Blocked or damaged fuel line
Say you’ve checked the gas tank and carburetor, and your mower still won’t start. If you find stale or evaporated fuel, the fuel line may be blocked too.
An improperly winterised mower may have had gas left in the fuel line, which then gummed up over time. You can feel along the line for any blockage.
Alternatively, check the line for any holes, cracks, or tears.
HOW TO FIX IT:
Follow your owner’s manual to disconnect the fuel line (be careful!). Inspect the fuel filter while you’re at it – if it’s broken, some debris may have entered the line and caused the block.
Carefully press along the line to push the blockage out. If this doesn’t work, or if there’s damage, it’s an easy part to replace.
6. Old or dirty spark plug
The spark plug is responsible for igniting the gas in your lawn equipment. A dirty or broken plug is a common reason for a mower that cranks but won’t start.
It’s also possible the plug is just worn out! It’s best to change a mower’s spark plug every 25-30 operating hours, with a maximum lifespan of 2 years with or without use.
HOW TO FIX IT:
You can clean a mower spark plug with some rubbing alcohol, but it’s easy to replace.
When buying a new spark plug, make sure to get one that matches your model code. Look up your model online or bring the old one to the shop.
7. Broken or dirty air filter
A malfunctioning or dirty air filter blocks air intake. If your engine can’t get air to mix with fuel, it won’t start.
Mowers with foam or hybrid filters need regular cleaning, and should be replaced every 300 hours of operation. Paper air filters should be replaced when there’s too much dirt on the folds.
It’s also possible there’s too much oil in your mower engine, which has leaked onto the filter. One sign of excess engine oil is white smoke coming out of your mower.
HOW TO FIX IT:
Inspect the air filter! If it’s dirty, you can clean the air filter and housing.
However, if the air filter is damaged, it’s time to get a new one.
8. Blocked gas cap
On the flip side, it’s possible you had too much gas or oil in the engine and it gummed up the gas cap.
The fuel cap has a tiny vent or several tiny holes that allow air into the tank. The vent also prevents a vacuum from forming in the engine, which stops gas flow.
Very carefully, try to start your mower without the cap. If it cranks and starts, the cap may be the issue.
HOW TO FIX IT:
Remove the gas cap and check for any blockages. You can clean it with a mild solvent, nozzle cleaner, or old toothbrush.
If there’s too much dirt or damage, replace the cap.
Tips for Lawn Mower Maintenance
Regularly clean and maintain your lawn mower and its parts, from the filter to the blades.
Use good-quality engine fuel and make sure you don’t overfill the tank with gas or oil.
If you’re planning to store your machine for a long time, empty the gas tank and thoroughly clean the mower. This minimises the risk of rust, mould, and blockages later on.
Don’t mow wet grass unless absolutely necessary! Some morning dew is fine, but anytime after rain or irrigation is a no-go.
