wow, thats Black, you must have tuned the motor to race speck, cause if thats only running in, then that piston should be still shinny, what your piston looks like there is how my pistons look after a big race event not when im running a motor in. see if the black carbon on the Piston just wipes away with a rag, if it dose then you are using a good quality fuel, if it needs polish to remove, then the piston is running dry and the Caster in the fuel is baking on the Head of the Piston.