Congratulations on the longest running thread yet (I think)
My .02 sez its the carbs. My eldo was running the same way when I got it, popping, poor idle, overly rich, ran better with the choke, etc. The only difference is that I have amals on mine. I rebuilt them (including replacing the slides), and found that on the 'popping' side that the idle jet was clogged, and therefore the main was used to compensate. That little passage was a real bugger to clean out, but now the bike runs like a champ! No popping even though I have the ez-flo-thru pipes. Of course, they're amals so...well, they're amals.