Corin Vuarrier-Lewis

Hi guys, I've had my Yamaha xvs 125 Dragstar since February this year. Everything has been running fine until now. I'm not sure what is wrong with the bike but it makes a really loud sound even when idling and the top speed is 30mph, people say I should get the engine reconditioned but really would just like to fit a new engine instead, except I can't find a second hand or new engine for my model anywhere. Can you guys help?