Why Won’t My Lawnmower Crank? (Top Causes Explained!)

Most of the time when a lawnmower won’t start the cause is a problem with the gas, the lawn mower carburetor or various filters being clogged inside your machine.

In this article, I’m going to tell you the top 7 reasons your lawn mower won’t start and what you can do about it.

Is your lawnmower out of gas?

It may sound crazy but checking that your lawnmower has gas is certainly key to it running! Adding a little gas is more often than not the missing link!

How old is the gas?

And how old was the gas? If it’s been sitting in the tank a long time or was old when you put it in this might just be your problem.

Gas has Ethanol in it, which gives gas a shelf life of around 30 days, if it’s older than that the Ethanol may have clogged your carburetor or caused corrosion.

Have you cleaned your fuel filter?

Just like your washing machine’s filter removing fluff, your lawnmower has a filter removing sediment from the gasoline.

If the filter is blocked, then the fuel doesn’t make it to the carburetor, and without that, your lawnmower is going nowhere.

First drain gasoline from the fuel filter into the drain pan, then use a clean cloth on the outside to wipe away dirt. Hold the filter at an angle, without allowing fuel to drip in your eyes or on your face, and look for debris on the filter. Be careful not to breathe in the fumes either! If you see debris on the filter or no light is passing through then it is time for a replacement.

What about the air filter?

The filter for fuel isn’t the only filter, you also have an air filter. This provides air to that pesky carburetor, so make sure you clean it! Equally, if the carburetor is torn it could allow debris inside, which can also stop your mower from starting. Air filters are also fairly easy to replace in most machines – but youll want to make sure you have an air filter that is specific to your model.

Here’s how to clean the filter

  1. Locate the air filter: A visual inspection is the first step, usually, they are on the side of the engine but not always so keep your eyes open!
  2. Remove the cover: It may have quick-release clips, screws or knuts. Make note of its position before you take it out for your inspection.
  3. Identify your filter: There are 4 different types of air filters. Pleated, foam, pre-cleaners/pre-filters, and dual-element air filters. Take a look online to identify the type you have. Once you have identified the type of air filter it’s time to clean. 
  4. Pleated air filters: These are designed to be disposable but if you give it a tap and remove some of the dirt you may get a little more from it yet.
  5. foam/pre-cleaner/pre-filter: These are designed to be cleaned. Try using warm water first, if it’s still not clean try it with mild dish soap. Don’t use any heavy soaps as these could leave a residue.
  6. Dual element filter: Essentially a pleated filter but with a foam covering to extend its life. Like the pleated filter, you can try cleaning it by tapping. Otherwise, it’s time to replace it.
  7. If you have tried it all and nothing works, replace your filter.

Is the battery dead?

Batteries should last a long time, sometimes there is no warning they are going dead. Check it with a voltmeter. The reading should be close to the battery voltage, so if it’s a 12V battery, your voltmeter should read around 12V’s. 

If your battery is rechargeable you’re in luck. Give it a few hours charge and you are ready to go. If that doesn’t work then a new battery is the only answer. Never try to open the battery.

Do you have a bad starter solenoid?

Is there a clicking sound when you turn the key in the ignition? Yes? Then it’s probably the starter solenoid. In which case your best bet is to replace this part.

Here’s how to replace a solenoid

  1. Ensure the ignition switch is off and the key is removed.
  2. Switch the mounting clip from the old solenoid to the new one. Place the new solenoid on the lawn mower’s frame.
  3. Attach the wires to the coil spades of the solenoid. Install the cables on the terminal posts
  4. There should be a gap for the battery box, put it in and engage the retaining tabs. The seat transfer clip is now to be reconnected to the seat bracket. Lower the battery and align the battery cables in the battery case.
  5. Reconnect the battery terminals, replace the insulating cover and you are ready to go!

Have you checked your spark plugs?

If you have been tinkering with your mower, check the spark plugs. You have inadvertently unplugged one. It’s a simple fix if so! 

 Your spark plugs may be dirty so it is also worth cleaning or replacing them, they’re cheap and easy to get.

Here’s how to clean the spark plugs

  1. Disconnect the spark plug lead from the spark plug and clean around the spark plug to avoid debris getting in the combustion chamber.
  2. Get your spark plug socket wrench and remove the spark plug.
  3. Use a wire brush and spray-on plug cleaner to remove any lighter areas of dirt. If it’s too heavy for that try using a knife but don’t use any abrasive to remove it.
  4. If your spark plug is damaged there is no question about it. It needs to be replaced.
  5. Use your spark plug gap gauge to check the gap between electrodes on the tip of the spark plug. A normal gap for small engines is 0.030. If it’s smaller you may not get a big enough spark and too big a gap may cause misfiring.
  6. Finally, you can reattach your spark plugs and leads. Make sure you don’t over-tighten the spark plug when reinstalling it.