Looks like there is a burn hole on the piston? Left side by intake window! Pop that piston out and lets see what the inside looks like and the top of the piston, transfers look pretty clean, what's the black spots just untouched?
Pics would answer your questions buddy. Also some answers to the questions that were being asked by previous members.. When you put the motor together did you proceed a proper break in. If the bike was rejeted for the pipe what jets did you use. Did you perform any leakdown test? Are your reeds working properly? The head would not be the solution to any of the problems that are accuring.