I have a 2002 Hustler Super Z 60in cut, with a 25 hp Kawasiki engine. It has 155 hrs on it. It has been dieing from time to time and won't start back without choking it. Today I was cutting grass and it started spitting and sputtering. Then it finally wouldn't run unless the choke lever was pulled all the way out with the choke on all the way. What is wrong with it and how do I fix it. Thank you in advance for your help.