kmx 125 starts speradically?

My bike starts when it feels like it sometimes it can take up to 20 mins to get it to start. i,ve changed the ht leads, coil, spark plug, compression tested and even changed the carburettor. The most puzzling part of it is it my start fine for up to a week then next morning its not starting again, once started it may run fine again for a week or the problem can be there when i start it later that day the bike is never left standing more than aday. I,ve had it in a garage and he says he cant find any thing wrong with it. can any body help plz.....