"At the bottom of my carb there is a plug in the carburetor flange, I think the idle mixture adjustment screw is under this cap, correct? If so how do I remove the cap? Drill it out?"
YES and YES. With a tiny drill bit say 1/8".
There is a screw on the lower part of the carb, on the side away from the engine. There is a mixture adjustment screw (MAS) plug covering it (if it hasn't been removed). This will have to be removed. To remove it, drill a hole into it (be careful not to drill into screw, put some tape around the bit so it can go in only a 1/4 inch). Drill off to one side not in the center. Then install a screw into the hole or a pointed object, and remove the plug with some pliers or by orying it out. Then turn the adjustment screw counter clockwise to make the mixture richer.
If this has no effect, then turn the screw in counting the turns (including how much you backed it off), until it is lightly seated. Then remove the screw and spring. Spray carb cleaner into the hole, then blow it out with [COLOR=green! important][COLOR=green! important]compressed [COLOR=green! important]air[/COLOR][/COLOR][/COLOR]
. Reinstall the mixture screw and adjust to the original position. If the idle smoothed out, then turn it in until it runs rough, then back off until it smooths out. If it is still rough then, back off the screw until it smooths out. If it doesn't, then the carb will have to be overhauled.