If this model has a fuel vapor check valve (usually hidden) in the top of the fuel tank, that is a likely suspect.
Like Scrubcadet10 said, try it with the fuel cap loose and see if it keeps running like it should. Many of the newer machines no longer have an atmosphere vented fuel cap. Air must get in the tank as fuel is being used. If not, cavitation (vacuum) occurs, and the engine gets starved for fuel.