There are at least two other threads on the MC34063 here.
The best way for communication is inside this thread, since so anyone other needing help will find info without asking.
Please post the V,I specs (VinMIN, VinMAX, Vout, IoutMIN, IoutMAX), and the configuration you are using (you can just tell which figure of the datasheet or of the app note you are following).
The Ton/Toff ratio you posted seems strange, if (as I guess, but don't know for sure) you are trying to convert from 5V to 15V.