Are you getting any smoke when its running rough? Next trip out, carry a jumper wire and go straight from battery to + side of coil, maybe even second wire to ground side. You will bypass the whole ignition wire harness this way. You might also add a temporary fuel gauge to monitor pressure at the carb.
Nothing mechanical will come and go, its either broke/worn or its not.
A lean condition will cause backfires and no smoke, so fuel pressure or delivery is a real possibility. Joe
