i have a tomos targa. i took my air box out because it would four stroke. the point is that the engine started popping. the day before i left i took the bikes cylinder off and cleaned everything up. one thing that i noticed was that there was a lot of carbon on the head and the pison and the exaust port had a lil more that the last time i cleaned it. all these parts had no carbon on then before i advanced the timing. could this be the reason for the carbon? and another thing... the piston had a brown is yellow kinda color on it. this color was found right after the rings and in the middle of the rings. does this mena my rings are dead? or could this be because i put a new piston in it and the new piston/ rings dont match my cylinder exactly. the cylinder had no scratches along with the piston.could the new piston be the reason for the popping? any more feedback.