Tors removed, so its not the handbrake.
left cylinder not fireing, i would say leaking oil seal on the ignition side (behind the stator) this would lead to sucking "false air"
also,
Let the bike idle and spray ether around the carbs, if you have any airleaks in your carbs or boots the bike will start reving up.
(a leak in the carb could be a lose or stripped carb top)
You checked your carbs, as a test you could try to open the fuel drain screwon the left carb to see if fuel is flowing to that carb aswell.
I hope this helps.