My push lawn mower had been running fine until this week. I pull the cord and the lawn mower starts for a second or two and then shuts off. I changed the gas, oil, and airfilter. Not sure what else to do. Looking for any trouble shooting pointers.

How old is the mower

I would check spark plug also check fuel supply hose. If u have 2 prime it check bubble

The fuel system probably has moisture contamination. Remove and clean the tank with carb and choke cleaner.