Mine had an intermitent popping at low RPM's under load. New Eddy carb that was ran one summer with about 2800 mile on it. I threw a new Holley on it. Almost identical pop persisted till I added a little jet to the primaries. It was lean on the primary circuit. I would agree with the cam lobe if it was more consistent. If it was a lobe it would be more likely to do it all the time, not just under load.