Carter bowl vents are notorious for allowing evaporation from the float bowls. Every AVS carbed motor I own does it. Electric fuel pump is one solution. As for a 'fire in the carb'? You'd be losing more than floats if that were true - you could be melting the castings and burning the car to the ground. Black smoke and running on 4 cylinders sounds like it's flooded. I'd chase the source of any 'backfiring' down first, like timing, crossed or bad plug wires, valves lashed too tight or burnt valves. And then buy new floats.