I agree with 4129R to check your timing. If that's good, I'd check your carbs. I'm assuming you're running Dellortos or Webers and your float level is set correctly...
Popping is normally a symptom of a lean condition. I am NOBODY's carb tuner but I'd turn one or more of your idle mixtures screws out a little. Which one? Since this is a new situation, I might turn out one idle mixture screw a half turn and see if it helps. If not, I'd turn it back and go to the next one.
HOWEVER, what I consider the real method for setting your idle mixture is in the attached file (which must be done with a hot engine). I have not been able to actually do that because my ear is not good enough to detect a 50 rpm difference reliably but I'll continue working on it. In the mean time I have gotten my car where it idles at a steady 1000 rpm and not pop or spit so I'm at least not embarrassed with the way it runs! I'm really proud of that!
But as I say, I'm nobody's carb tuner so I have a lot of room for improvement.