Hi there,
This happened to me too.I have an r50x (r70x) and I took it back to the shop and they fixed it free of charge,as there has been a problem with this.
I have been riding it now for nearly one year and no problems,the only complaint I have is, with the new cdi,it has a rev limiter on it,so need to get an AFTER MARKET (Malossi)cdi to get full revs.
ALL THE BEST,,,,,,,,,,,,ENJOY THE RIDE