If it were a Holley, I'd say "power valve"... but it's not a Holley. A pop out of the carburetor sounds like an intake valve is not sealed all the way and the fuel in that cylinder is igniting back up through the carburetor. A bent intake valve, bent pushrod or funky rocker all could do that, or even a weak valve spring or burnt valve seat. Maybe run a compression test & see if one cylinder is really low compared to the others?

70 Roadrunner convt. street car 440+6, NOS, 4-spd, SS springs '96 Mustang GT convt. street car '04 4.6 SOHC, NOS, auto, lowered "Officer, that button is for short on-ramps"