I am going to assume that you have a ZD1011 Kubota Zero Turn Mower.
Check your air filter and fuel flow to the injection pump. The fuel flow can be checked by removing the rubber fuel hose at the injection pump, holding the hose over a catch can or bucket, and turning the key switch to the RUN position. Do not start the engine.
You should have a good full stream of fuel that is pulsing coming from the hose. If not, you have restricted filters or debris in the fuel tank that's plugging the fuel supply. You can check the flow from the tank to the first filter by removing the hose to the filter and seeing if you are getting a good flow there. It is located right behind your heels when setting in the seat.