Those would be the plugs that cover the idle mixture screws. They made a special cutter for removing them. I still have mine somewhere. You can get them out with the carb removed. Use a small punch or caping chisel and cut the base out from the bottom to knock them out. That method does tend to leave the carb looking a little butchered. A couple small cuts on each with a hack saw will make it a little cleaner.
If you are having drivability problems I doubt if the idle mixture adjustment will help much.