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.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop