My bike did the popping thing and it is cured by a full clutch pushrod adjustment. This is the procedure where you slacken the handlebar adjustment right off and then do the clutch pressure plate adjustment.

My 1967 bike also suffered from a lack of clutch cable travel. The clutch dragged really badly. In my case it was the cable nipple at the gearbox end getting caught on the abutment that screws into the top of the outer gearbox cover. I think that the cable nipple position is lower down on your bike so this might not be able to happen.