Just a thought but it may be miles off....if your mower has a Briggs engine with the fuel tank on the side, the fuel is actually pumped to the carb (using crankcase vacuum) via a rubber pipe that connects from the engine to the carb itself. If this pipe has come off, no fuel gets pumped through. Failing that, look for air leaks around the pipe that draws fuel from the tank.
John
March 2008