Hello, first - if it looks like a screw, as in a slotted screw head then it is not a plug but a AF screw. If it looks like a half circle or "D" then is not a plug but a spec head on the AF screw. If it is a flat surface it is a plug. If is a anti-tamper plug I will not say it can't be removed while on the bike but you will have to creative and agile. A small hole will need to be drilled in the end and use something to
get a bite into the plug and leverage it out. If it is a "D" head adjustment screw some people use a Electrical Butt connector heated until soft and pushed over the head and allow to cool. That can then be used to either extract the "D" head and replace or use as is withe the connector end as the thumb knob.
Not sure if that helped or not. Using a mirror you can do some further investigation and see what you have and proceed.
For what it's worth - the numbered thumb adjusting screws are really nice to replace the OEM slotted adjustment screw.
It's a tight area to try and work and rotating the carb bottom to the left really helps do any work on the carb. Loosen the boots and give the throttle cable some slack and it will rotate fairly easily.
Geez, that seemed like a lot of chat for a simple thing. I think I'm becoming Jim !
](./images/smilies/eusa_wall.gif "Brick wall"){kind=small}
