Popping sound coming from the carb while driving at highway speed. what could it be?

The popping sound is backfiring this occurs for a few reasons one reason is your vehicle is running to rich or to lean this happens when you don't have the proper fuel and air mixture you can adjust this with a screw on the side of the carburetor. Another reason could be that your vehicle is firing to late or to early you can adjust this by retarding or advancing your distributor.