How to identify why my apprillia habana custom 50 wont start?

Hi, Basically i was ridding my apprilla habana custom 50cc for about a hour then it decided to gradually slow down then cut out. I checked the spark plug instantly and it had a good spark. Starting motor sounded fine and turning over but the bike just wouldnt start. Have had problems with my drive belt and have replaced it correctly via haynes mannual but had suggestion from a friend that the centerfugal clutch may be jammed opened forcing the bike to remain in top gear (preventing it from starting). Really at wits end with it, Any suggestions would be much appreciated. :)