Many problems can cause a Murray walk-behind lawnmower to stop running. However, the mower's engine, with a simple design, needs three basic things to start and stay running. Check the Murray lawnmower for fuel and oil, a proper spark and enough air. Get all these three components back in line to keep the mower running.
Before each use, open the fuel cap and check the level of fuel, making sure it is at least ¾ full before starting it up. Low fuel levels are the cause of many running problems. Also, make sure the fuel is a higher grade regular unleaded gasoline with a rating of 87 octane and higher. Don't use gasoline that is blended with ethanol, and never use diesel fuel. These will damage the carburetor and fuel system. Fuel older than 30 days also should be disposed of as it can also damage the fuel system.
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The crankcase and piston need constant lubrication. Otherwise they will start overheating, and the engine will shut down. Oil also should be checked before each use to ensure a sufficient supply for the job at hand. Put the lawnmower on a level surface before checking the oil. Pull out the oil dipstick, wipe it off with a rag and insert it again. Pull the dipstick out and check the oil reading. If reads "Add," slowly add more oil to the oil tank, according to the engine's oil specifications. Also check the low oil automatic shutdown switch, which can be activated by trapped air during an oil change.
The fuel valve switch must be fully engaged in the "On" position for the fuel to flow through the carburetor and cylinder. Engage the "On/Off" switch fully into the "On" position as well. Inspect the wires leading to the switch for any damage, corrosion or loose connections and replace wires if they're damaged. Remove the rubber boot on top of the spark plug, unscrew the plug with a socket wrench and pull it from the cylinder. If the electrode gap is dirty, corroded or damaged, replace the spark plug with a new one.
The lawnmower engine must get sufficient air into the engine and expel heated air. If the intake and outtake air ports get clogged with dust or other material, the mower will automatically shut down to prevent further engine damage. Pull out the air filter after every three to four uses and clean it according to the mower's specifications, as some may require a washing. After every 60 hours of operation, pull the spark arrestor screen from the muffler and scrub the muffler and screen.