Hello dear comrades, I have some problems with the star behavior of my Yamaha XS 250, it starts badly, and when started, it has from 7000 rpm quite stutterer or offseter. the left candle becomes very fast black and rusty, the right candle becomes rather light brown to white. Since I am relatively new owner and not yet experienced with 4-strokes, I now do not know exactly where to start with the troubleshooting, since someone has a tip for me ?