Hello Rod, Margo is right on with the visitors visa, you can only stay for 90 days. Some of the tourists take into consideration going to Belice for a few days (If I'm not mistaken, you have to be 72 hours out of the country).... BUT! You can go to migration, La Ceiba would be the closest one to Utila, and get an extension. Some people don't know it, but it's cheaper to get a month extension than leaving and coming back into the country.
I live in La Ceiba, I lived for most of my life as a child in Florida. I don't know if I would recommend Utila for so long, it is pretty affordable though. Try touring the country instead. That's only my opinion though.
Let me know if you need any help with travel arrangements, I have friends who own a tour operator and can find you affordable rates in different hotels.