Lawn Mower Starts But Does Not Stay Running

So, your lawn mower starts up with a promising roar, but then sputters and dies a few seconds later? Frustrating, isn't it? This is a very common problem, and thankfully, often a fixable one. It usually points to an issue with the engine not getting a consistent supply of fuel or air. Don't worry, we'll walk through the most likely culprits and how to troubleshoot them. Think of me as your virtual service advisor – let’s get that mower purring again.

Common Causes and Their Solutions

Let's break down the most frequent reasons why your lawn mower starts but doesn't stay running:

1. Fuel Issues

This is the most common category. Fuel problems can manifest in several ways:

• Old or Stale Fuel: Gasoline degrades over time, especially when exposed to air. It can become gummy and clog the fuel system.

Solution: Drain the old fuel completely. Use a siphon or tip the mower (carefully, following safety instructions – disconnect the spark plug wire!). Refill with fresh, high-quality gasoline. Adding a fuel stabilizer to the fresh gas can help prevent this issue in the future, especially if you don't use your mower frequently.

• Clogged Fuel Filter: The fuel filter prevents debris from reaching the carburetor. A clogged filter restricts fuel flow.

Solution: Locate the fuel filter (usually in the fuel line between the fuel tank and the carburetor). Replace it with a new one. Fuel filters are inexpensive, typically costing between $5 and $15.

• Clogged Carburetor: The carburetor mixes air and fuel in the correct ratio for combustion. A clogged carburetor is a very common cause of starting problems. Old fuel, as mentioned before, is a prime culprit.

Solution: This is where things get a little more involved.

• Simple Cleaning: Try using carburetor cleaner spray. With the engine off, spray the cleaner into the carburetor's air intake. Let it sit for a few minutes, then try starting the mower. This might dislodge some minor debris.
• Carburetor Removal and Cleaning: If the spray doesn’t work, you’ll need to remove the carburetor. This requires some mechanical aptitude. You’ll need wrenches, screwdrivers, and carburetor cleaner. There are plenty of online tutorials that show you how to do this for your specific mower model. Carefully disassemble the carburetor, clean all the jets and passages with carburetor cleaner and small wires or carburetor cleaning tools. Reassemble and reinstall the carburetor. Be sure to take pictures before you disassemble it so you have a reference for reassembly.
• Carburetor Replacement: If cleaning doesn’t work, or if the carburetor is severely corroded, you may need to replace it. Carburetors can range in price from $20 to $100 or more, depending on the mower model.
• Faulty Fuel Cap: The fuel cap needs to vent properly. If the vent is clogged, it can create a vacuum in the fuel tank, preventing fuel from flowing.

Solution: Try loosening the fuel cap slightly. If the mower runs with the cap loose, the cap vent is likely the problem. You can try cleaning the vent hole (usually a small hole on the cap), or replace the fuel cap. They're relatively inexpensive.

2. Air Intake Issues

The engine needs a proper air-fuel mixture to run correctly. Restricted airflow can cause problems.

• Dirty Air Filter: A clogged air filter restricts airflow to the carburetor, leading to a rich fuel mixture (too much fuel, not enough air).

Solution: Check the air filter. If it's dirty, clean or replace it. Foam filters can often be washed with soap and water, then oiled lightly. Paper filters should be replaced. Air filters are usually cheap, costing between $5 and $20.

• Obstructions in the Air Intake: Check for any obstructions blocking the air intake, such as grass clippings, debris, or even a bird's nest (it happens!).

Solution: Remove any obstructions. Use a brush or compressed air to clean the air intake area.

3. Spark Plug Issues

The spark plug ignites the air-fuel mixture in the cylinder. A faulty spark plug can prevent the engine from running consistently.

• Fouled or Damaged Spark Plug: A spark plug can become fouled with carbon deposits, oil, or fuel. It can also be cracked or damaged.

Solution: Remove the spark plug. Inspect it for damage or fouling. Clean it with a wire brush or replace it. Ensure the spark plug gap is correct (refer to your owner's manual for the correct gap). Spark plugs are generally inexpensive.

• Loose or Corroded Spark Plug Wire: A loose or corroded spark plug wire can prevent the spark from reaching the plug.

Solution: Ensure the spark plug wire is securely connected to the spark plug. Clean any corrosion from the wire terminal and the spark plug terminal.

4. Other Potential Problems

• Low Oil Level: Some lawn mowers have a low-oil sensor that will shut off the engine to prevent damage.

Solution: Check the oil level. Add oil if needed, using the correct type of oil as specified in your owner's manual.

• Faulty Safety Switch: Lawn mowers have safety switches (e.g., on the handle, under the seat) that are designed to shut off the engine if the operator is not in the proper position. A faulty switch can cause intermittent problems.

Solution: Try engaging and disengaging the safety switch several times. If that doesn't work, you may need to have the switch tested by a qualified mechanic.

• Choke Problems: The choke enriches the fuel mixture for starting a cold engine. If the choke is not functioning properly, the engine may not stay running.

Solution: Ensure the choke is operating correctly. If it's manually controlled, make sure you're adjusting it properly. If it's automatic, it may need to be adjusted or repaired by a mechanic.

Tools You'll Likely Need

Here's a basic list of tools that will come in handy for troubleshooting this issue:

• Wrenches (various sizes)
• Screwdrivers (flathead and Phillips head)
• Spark plug wrench
• Pliers
• Carburetor cleaner spray
• Fuel filter
• Spark plug
• Air filter
• Funnel
• Oil (correct type for your mower)
• Rags
• Safety glasses
• Gloves

When to Call a Professional

If you've tried the above steps and your lawn mower still won't stay running, it may be time to call a qualified mechanic. Complex engine problems, such as internal engine damage or issues with the ignition system, may require professional diagnosis and repair. Also, if you're not comfortable working on engines, it's always best to err on the side of caution and seek professional help. Attempting repairs you're not qualified to perform can lead to further damage or injury.

Approximate Repair Costs: The cost of repair can vary greatly depending on the problem and the mechanic's labor rate. A simple carburetor cleaning might cost between $50 and $100. A carburetor replacement could cost between $100 and $250. More complex repairs, such as engine rebuilding, could cost several hundred dollars or more. It's always a good idea to get an estimate from a few different mechanics before authorizing any repairs.

By following these steps, you can hopefully diagnose and fix the problem yourself and get your lawn mower back in action. Good luck!