Flame coming out of the carburetor indicates a cylinder is firing while the intake valve is open. Possible causes are many (stuck or burned intake valve; valve timing; timing chain skipped tooth; spark plug wires on on correct wires; defective vacuum advance; cracked or carbon track in distributor cap; defective carbon spark plug wires; more).
Would suggest starting with a compression test, which will tell you the condition of the valves.
It doesn't take many backfires to melt the venturi cluster in the carburetor.
Jon.
