After rereading your original post, this seems to be a fuel problem, not an ignition problem. The popping could be caused by excess fuel sitting in the intake manifold where the hot gases from the intake valves is igniting it, or the valves themselves due to carbon buildup. The plugs getting black is a sign of excess fuel in the cylinders, which supports that diagnosis. After driving it a little, return to the garage. Remove the carb and look into the manifold with a flashlight. If the manifold is wet at all, that's a confirmation that too much fuel is getting in to the manifold.
However, you also state that you have to choke the carb to keep the engine running. That is counterintuitive to the other symptoms you describe. Choking indicates fuel starvation. So it appears you may have at least two problems. You can only solve one problem at a time.
If it were my truck, the first thing I would do is tear the carb down again and go over the rebuild step by step, making sure every setting is precisely correct, every valve is free, functioning correctly and not burred or nicked or sticking for some reason. As you're rebuilding it, make sure that the float is free to move through its entire range of motion and not hanging up on anything. Sometimes a gasket can overhang enough to cause problems with float movement. Make sure the float valve is able to move freely as well, doesn't stick open or closed and seals properly.
