Well i managed to fix the problem by pulling each of the NGK BP6ES spark plugs, cleaning them with a wire brush and electronic contact cleaner, spraying contact cleaner to each of the terminals of the distributor cap and pertronix ignitor. I also filled up a Little bit more of Castrol 10w 30 engine oil in each of the carbs. Retuned each carb and balance them raising the fast idle screw to 1,500 RPM. I set the idle mixture knobs in each carb to 3.5 turns and the idle RPM to 1,000 RPM. At the moment no backfire or engine shut down. I will keep testing tomorrow and keep you posted! I need to sort this idle issue first before i install the AC system. Question: Are these NGK BP6ES spark plugs pregapped from Factory? or will i need to get a feeler gauge? If so what is the gap?