Wow, thank you for posting this. I just restored a 1973 Eldorado and this is the kind of thing that keeps me up at night. Some observation that might help: - the two pistons have different rings, some work was done at some point to give old top end a new life (I am doing that myself!) - the blown one has all ring stuck. IF the rings stuck before the event, chances are you had low compression. That in turn will make the mixture lean despite perfect carb tuneup and perfect timing. At least that is the conclusion I would come to if this was my bike. The other piston has carbon deposit, it might be fine. What would I do? I would make sure the rings move freely in the groves. Then I would test the compression. You can loan a compression test tool from OReilly for $0 (they charge you a fully refundable deposit). I have done it, my old chrome lined cylinder were at 130/135psi, low but within acceptable range. I rode 100mi on them before one of them started to blister and the free ride was over. Anyway, anything approaching 100psi or less and it is time to rebuild. Hope this helps. [all reading this] BTW I am on the market for an Eldorado piston since I damaged one of mine during cylinder swap (I am putting iron sleeved cylinders on). PM me if you have one, please. Good luck!