sxrbandit, with the skirt being broken would indicate to me that the piston skirt was worn beyond spec from not having the rings changed often enough, the piston does not hold stabilty in the bore and begins to rock back and forth cracking the skirt off, its those peices of skirt that were inhaled in the case up thru the trnasfer ports and on top of the piston.
jk auto, yours looks like a lean burndown, probally asscociated with mid range cruising speeds, this is why both pistons show the signs of slow burning off the piston crown edge, if you leaned out the needles you might have answered your own question as to why if the carbs were indeed clean. Most times if its a wide open burndown the ring will be bent up and melted as the crown is taken away, it becomes red hot,soft , bends and then catches the exh port from the high rpm lean condition.
