Electronic ignition issue

Just a thought you said popping noise could you have a valve that is sticking. Maybe a little trans fluid down the carb while running may help sense it sat. And i have had this problem once couple cylinders not firing. I had a valve job done and painted the heads when put back togather. I had the plugs out when painted and the spark plugs werent grounding. Maybe try cleaning spark plug holes on cylinders in question.