Hello, I have inherited a zx25 from my grandpa, they have completely polished and cleaned through yet when I drive now I come in loud tacho in the second course on 40-50 km/h I don’t know if what was done about it or if that is the original condition. I need help to get back on something this 25km/h or should I have a mechanic come? P.s entered in the papers with 25km/h Thank you in advance Maxi