There’s a special kind of frustration that comes with a lawn mower that starts on the first pull, only to sputter and die a few seconds later. You feel a brief moment of victory, quickly replaced by the realization that your yard work is still on hold. The good news is that this specific problem is often one of the easiest to diagnose and fix yourself, saving you a trip to the repair shop.
When your lawn mower will start but not run, it’s almost always a sign that one of three essential elements is being interrupted. Your engine needs a steady supply of clean fuel, consistent air flow, and a strong spark to keep going. A disruption in any one of these areas is the usual culprit. Let’s walk through some simple solutions to get you back to mowing in no time.
Checking the Usual Suspects First
Before we get into more detailed checks, always start with the simplest possibilities. Is there fresh fuel in the tank? Old gasoline, especially the ethanol-blended kind, can go bad in as little as 30 days, forming gums and varnishes that clog the engine. If the fuel is from last season, safely drain the tank and the carburetor, and fill it with new gas. Next, check the oil. While low oil won’t always cause this specific issue, many modern mowers have a safety sensor that will shut the engine down if the oil level is too low, so it’s a quick and worthwhile thing to verify.
Lawn Mower Will Start But Not Run: Simple Solutions
Since the engine starts, we know the spark plug is working at least initially. The problem is likely that the engine is being starved of fuel or air after that initial start. The most common cause for this is a dirty or blocked carburetor. The carburetor’s job is to mix fuel and air in the perfect ratio for combustion. Over time, tiny particles from degraded fuel can clog its tiny ports and passages.
You can often clean the carburetor without even removing it. Locate the carburetor bowl (a small, bulb-shaped metal cup underneath the carburetor). There is usually a single bolt holding it on. Place a small container underneath to catch any fuel, and carefully remove the bowl and the gasket. Clean out any sediment you find inside the bowl and the carburetor body with a small brush or cloth. Reassemble it and try starting the mower again.
Don’t Forget the Air Flow
Your mower’s engine needs to breathe. A clogged air filter can choke the engine, preventing it from getting the air it needs to run after the initial fuel in the carburetor is used up. Locate the air filter cover—it’s usually a large, plastic box on the side of the engine. Unclip or unscrew the cover and remove the filter. If it’s a paper filter, hold it up to the light. If you can’t see light through it, it needs to be replaced. If it’s a foam filter, you can wash it in warm, soapy water, rinse it thoroughly, let it dry completely, and then apply a few drops of clean engine oil before putting it back.
When to Check the Spark Plug
While a completely failed spark plug will prevent starting altogether, one that is failing or heavily fouled with carbon can cause the engine to start and then die. It’s a good final step in your diagnostic process. Remove the spark plug wire and use a socket wrench to unscrew the plug. Inspect the electrode at the end. If it’s covered in black, sooty deposits or the gap looks excessively wide, it’s a good idea to simply replace it with a new one recommended for your mower model.
By methodically checking the fuel system, air filter, and spark plug, you’re addressing over 90% of the issues that cause a mower to start but not run. These simple solutions require minimal tools and can restore your mower’s health, turning a moment of frustration into a satisfying DIY success.