Do you have the vacuum advance line connected to the fitting at the venturi area on the carburetor, or to full manifold vacuum? You've got over-advanced timing for some reason, either an incorrect setting of the ball & pointer, or too much vacuum on the advance unit. Try turning the dizzy housing clockwise with the advance connected a little at a time during a test drive until the pop goes away.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!