I have been running a WS7 for the last year and a half, aprox 5-6 gallons. I decided to pull the motor apart for a little PM, and noticed a proportionaly large amount of carbon build-up just on the top of the piston. After some carefull cleaning I also noticed two very small nicks in the top of piston maybe from a coil on the plug. I was wondering what caused the build-up ie. tune, fuel, wrong plugs, and if the nicks in the piston itself would hurt performance or tune. I have been running OD 77t and 97t plugs. The rest of the motor is basically spotless and it ran fine prior to tear down.