Why wont my mower wont stay running *READ ALL*?

Sounds to me like it isn't getting enough fuel. Could be water and or debris in the float bowl. I agree that the factory settings are probably lean to begin with to limit pollution. I guess what I would do is clean the carburetor. At the same time I would look at the main jet and talk to the local repair shop and see if you could go a size larger. Look into your fuel tank and see if there is any dirt or water. Water will look like blobs on the bottom. also look inside the float bowl for the same thing. Make sure that all the fasteners are tight around the carburetor.