I've got a new Briggs and Stratton push mower I used only about 4 times without any problems. Started on the 1st pull. Today it starts on the 4-5 pull and runs about 2 seconds and stops. The filter and spark plug look fine and yes it has gas and oil. Any ideas what to check next?
Tekajake

It sounds like it is filling with gas and then the gas gets burned off and stalls because there is a clog somewhere not allowing enough fuel to sustain its operation. Fuel filter, Air Filter and fuel lines should be checked for obstructions.

Another possibility is gas left in there for a period can affect the carburetor, getting it so dirty as to affect its performance. If this is the case, you would need to remove it and clean it with carburetor cleaner, being careful not to spray any rubber or plastic parts.

Have a toro lawn mower walk behind and some times won't start and now will not stay running changed primer bulb air filter and cleaned the carb