First, take the fuel line off the carb and turn the petcock on, if fuel pours out, then tap on the sides of the float bowl, you may just have a stuck float. If that still doesn't work, take the carb off and take it completely apart and clean everything, also check the float adjustment. If no fuel comes out of the fuel line when you pull it of the carb, then your problem is a bad petcock, clogged fuel line, filter or blockage in the tank. If the machine has been sitting for a while, I would definately start with fresh gas and give the inside of the carb a look.
Yours truly, sincerelly, love always, Josh aka The DirtDemon.