Troubleshooting When Your Lawn Mower Will Not Start

What to do when your walk-behind or riding lawn mower won't start

You're all set to mow the lawn, but when you go to start your machine, nothing happens. There could be several reasons why your lawn mower will not start, including something as simple as skipping a step in the starting process. Plus, depending on whether you have a walk-behind or riding lawn mower that won't start, you could have a different root cause for the same problem. Here are some troubleshooting tips to find out what went wrong, what lawn mower parts you need to fix it, and if you'll need to take your lawn mower in for professional service.

Check the startup process in your operator's manual

It seems simple, but sometimes you just forgot a step in the process. Before doing anything else, download the MTD operator's manual  for your model and go through the steps to start your mower up again. You may need to engage the control handle, connect the spark plug wire, check the battery, and activate the choke and parking brake if you have a riding lawn mower. If your lawn mower still will not start, move on to the next step below. Keep that operator's manual close by as you will use it to identify any replacement lawn mower parts you need.

Clear out the old fuel

If your walk-behind or riding lawn mower won't start, the culprit may be old fuel. Stale fuel that's more than 30 days old and has not been modified with stabilizer will not combust and your engine will not start. Siphon or drain the old fuel from your mower, dispose of it properly and replace it with fresh fuel. If you're unsure whether or not the fuel is stale, you can test it with Fuel Defense(TM) test swabs, which you can order online from MTD Parts. 

In addition to failing to combust, old fuel that has been stored in your mower without stabilizer for an extended period of time will begin to leave deposits as it breaks down. Your engine, lines and carburetor can become gummed up or blocked by the old fuel deposits. You'll need to take your machine in for professional lawn mower service if your carburetor is gummed up or damaged by old fuel. 

Find out if fuel deposits are the reason your lawn mower will not start by removing the spark plugs. If you don't smell fuel in the combustion chamber or on the spark plugs, you probably have blocked fuel lines. Use a spray carburetor cleaner or pressurized air to try to clear things out. 

To avoid the hassles that come with old fuel, use an additive like StaBil in your gasoline and change out the old fuel at the end of the season. 

Replace the spark plug

After a few years your spark plugs will have accumulated too much dirt and deposits to function properly, and the buildup on the electrodes can prevent a spark. If the damage or buildup is not too bad, you may be able to clean the plug. Otherwise, if it has become corroded beyond repair you'll need to replace it. You may also simply have a problem with the gap between your spark plugs. Check your operator's manual for the proper distance and adjust it.

Clean or replace the air filter 

When you mow, dirt and debris gets sucked up into your machine. That's why there's an air filter on it. But if your filter has become full and dirty, the debris may also work its way into the engine and your lawn mower will not start. Clean or replace the dirty air filter and change out the contaminated fuel. If you have a push or walk-behind mower, you want to be careful when changing out the fuel not to tip the mower on its air filter side as this can cause oil to leak into and clog the filter.

Lawn mower won't start? Try replacing the air filter with a genuine MTD Parts air cleaner kit.

Take your lawn mower to an MTD service center 

If none of the above tactics work, you can check out our tool to diagnose and troubleshoot your mower  or take it in for lawn mower maintenance at a local service dealer. One of the last possible reasons for a lawn mower that will not start is a failed engine ignition coil. It's rare and you'll need to test for electrical activity with a spark plug circuit-testing tool. This lets you safely check the flow of the electrical current from the ignition coil to the spark plug terminal.  If there's no electric activity, you'll need to take it to a professional for inspection and repair.

Order the lawn mower parts you need from MTD Parts 

Once you diagnose why your walk-behind or riding lawn mower won't start you can order the proper MTD lawn mower parts  you need to make repairs. Use your operator's manual and our Parts Finder to get what you need. Of course, it's always wise to have a few items on hand to make quick repairs when necessary. Consider keeping these in stock from the start of the season:

• Clean air filter
• Fresh fuel with stabilizer
• New spark plug
• Spark plug wrench or socket tool

You may also want to find a local MTD service dealer  so you can bring your lawn mower in for maintenance when a repair is outside your area of expertise.