![]() In the future, if you're going to leave gas in the tank for a while, add fuel stabilizer. If your gas has been sitting around a while-either in the tank or in the can-drain the tank and fill it with fresh, clean gas from a clean gas can. Old gas that has absorbed water or gas that has dirt in it can keep a mower from starting. For these tests, be sure you’re in a well-ventilated area where gas fumes can’t build up.įirst, let’s look at the condition of the gas. Now, if the engine started and ran briefly when you did the starting fluid test, you know the spark and compression are okay and the problem is in the fuel system. The technician has the right tools and the expertise to diagnose low compression. If it’s lower than 40 psi, have a service technician examine the engine and fix the compression problem. ![]() The gauge should measure between 40 and 60 psi of compression. Pull the starter rope repeatedly, until the needle on the gauge stops rising. Insert a compression gauge in the spark plug hole and push the button to zero-out the gauge. ![]() You need a compression gauge for this test.įirst, remove the spark plug from the cylinder and pull the starter rope several times to purge fuel or oil from the cylinder. If the spark plug is good and the ignition system works, check the cylinder compression. If the tester shows that there’s no spark, follow the steps in our video about troubleshooting the ignition system. Pull the starter rope and see if the tester sparks. Clamp the bail control bar down to release the blade brake. Connect the tester boot to the spark plug and connect the spark plug wire to the other end of the tester. Release the rope from the mower handle so it's in reach when testing the spark plug. If the spark plug looks good, reinstall it and then connect a spark plug tester to check the ignition system. If you see excessive buildup or a crack, replace the spark plug. Also, look for a crack in the ceramic insulator. Look for carbon or oil buildup on the spark plug electrode that could prevent sparking. Pull off the spark plug wire and remove the spark plug, using a ratchet fitted with a deep socket. Spark plug and compressionĬheck the spark plug first. If the engine starts and runs briefly, click here to skip to the section about diagnosing fuel problems. If it doesn't start, that eliminates a fuel problem, leaving spark and compression on our list of suspects. Spray starting fluid through the air filter opening to the carburetor and then try to start the engine. While the air filter is removed, let’s do a quick test to see if the engine has a fuel problem. If your mower has a foam air filter, you can find cleaning instructions in your owner’s manual. If it’s completely clogged, then you need to replace it. If you have a paper filter that’s just a little dirty, you can tap the filter on a hard surface to clean it. This mower has a pleated paper filter, but yours might be a different type of paper filter, or it might be foam. Remove the air filter cover and pull out the air filter. Check the air filterĪ clogged air filter can keep air from getting to the carburetor and mixing with the gas. We’re going to start by checking a few easy things. ![]() To fix your problem, we’ll have to figure out which of these three is missing. Finally, it needs the right amount of compression in the cylinder to drive the piston. Then it needs a spark from the spark plug to ignite that fuel in the cylinder. The first is fuel, which is a combination of gasoline and air that mixes in the carburetor. Since we’ll be working around gasoline, choose a well-ventilated area free of open flame or sparks.įor an engine to start and run when you pull the recoil starter rope, it needs 3 things. These are the tools and supplies you might need, depending on the problem. Although your mower might look different from this Craftsman 21-inch mower, they all work pretty much the same. Today we’re talking about some troubleshooting steps to figure out why your lawn mower won’t start. ![]()
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