Honestly, your engine looks fine. A little carbon buildup never hurt an engine. In fact, many of the European fuel suppliers put organic content in the fuel to create carbon deposits inside the engine under the theory that it helps to seal the piston to the sleeve. The only thing you really need to worry about is when the top of the piston and the head get "speckled" or appear sandblasted. That means that you have too much compression and it's pingin'!
