I have a Gravely zero turn with a 15 hp Kawasaki I bought used a month or so ago with 325 hours on it. The machine is clean well taken care of and runs like a champ...... until the other day I was using the mower and after about 20 minutes it sounded like it was starting to run out of gas and die. After doing that for a minute or so it completely died. I turned the choke up, turned the key and it fired right up and was fine for 5 minutes or so then the same thing. Im guessing its a carb/fuel problem but has anyone had this happen? Where should I start.