Ignition....somewhere. The loud pop and resultant backfire (causing the interior of carb to blacken) is the ignition coming back "on Line" and back firing. Check the heavy black and red wires from the MSD box, then check them again, then check the small red one that goes to a switched 12 volt source. Once those are deemed good do this:
http://www.msdignition.com/1troub1.htm
You may want to check ignition switch too.
Fuel will normally cause it to nose over and if rectified, start again but not "POP".