Most running problems on a Poulan Pro push lawn mower occur due to a decrease in the air and fuel supply needed to power the combustion engine. If the fuel tank and oil supply are fresh and topped off and the engine still won't stay running, a thorough inspection and cleaning of the fuel and air systems will be required.
Dirty Air Filter
The air filter expunges any particulate matter in the air that would otherwise damage the piston or the cylinder walls. However, these filters trap so much particulate matter that they can choke up and kill the engine. Most often, a dirty air filter will allow combustion to begin, but as the engine accelerates, requiring a larger amount of fuel and air, the supply will be too restricted to maintain adequate power. Remove the filter after each use, and slap it against your palm. Wash the filter after every 10 hours of operation.
The muffler pushes out all heated, combusted gases from the crankcase and cylinder. As these gases leave through the exhaust port and muffler, a small portion of those gases go back to a liquid state and get trapped on the muffler walls, the spark arrestor screen and the exhaust port. When these carbon deposits build and harden, they will gradually choke off the engine, which will fire but won't stay running. Open the muffler and scrub the walls, the screen and the exhaust port every 60 to 80 hours of operation.
Dirty Fuel Passages
If after cleaning the air passages, the mower still won't stay running, take a look at the fuel system. Fuel needs to travel in a circuit from the tank, through the hoses, to the carburetor and back. Over time, fuel impurities and bad gas will also build up gradually along the tank walls, the fuel hoses and the fuel filter. Dirt and other material may also have gotten trapped in the tank and, when the engine starts pulling gas in, the trapped material may suck up against the filter or hose, stopping gas flow. Clean out the fuel tank, wash the fuel tank cap in soapy water, scrub the tank walls, pull out and replace the fuel filter every season and replace the hoses every other season.
Bad or old gas happens frequently as gas will go bad after just 30 days. If the gas is used after this time, a small residue will gradually build up in the inlet and outlet bores inside the carburetor, which will cause a severe drop in engine performance and eventually shut your engine down. Never use any gas older than 30 days; just pour it into your car and start fresh; Always store the machine without gas in the tank or carburetor. If running problems persist, pull out the carburetor, disassemble and clean it.