If the mower fires and then dies out, or, the mower runs however begins to loose power and dies out... drop the 1/2" bolt that holds the carburetor bowl assembly on - use either a box/circle wrench or 1/2" socket. Remove the bolt from the bottom of the bowl and make sure not to loose the plastic washer for the bolt. Also, when dropping the carburetor bowl, do no loose the gasket that fits inside the upper ring of the bowl.
Before you dump any fluid (gas) in the bowl, make sure there is no water in your gas. Next, after dumping the liquid, clean the bowl of any dirt/debris. Next, inspect the 1/2" bolt - there are two opposing pick-up holes (180 degrees) plus on that runs up the length of the bolt - make sure these are clear of any debris.
Reinstall the bowl, bolt with washer and tighten. Assuming there was some dirt and debris in the bowl/bolt that has been removed - your mower should start up like a champ.