Unfortunately I am so old that when I push the button to take the picture I move the camera. It is simply a very fine screw thread that bites in the plastic when you turn it and push a little at same time. sorry
This picture shows most of the parts in a carb. You take it all apart with those 7 screws. Now those two rubber looking device are two pieces that I leave together if I am going to reuse them. These are very simple the only thing is to be sure which way to put the gasket/diaphram back on. The three pieces at the bottom of the picture is what I put in the soaker/vibrator machine..
This poor picture shows how nicely a pencil cut off can be used to push the screen back into the hole in the carb. That spring can be squirrely and pop off the table and be gone forever.
I cut a piece of wire to help put the spring back in place when I am about to reassemble. Fingars just won't do it for me that spring can also jump all over.
This bad picture is trying to show the wear surface that sometimes causes a lack of gas pumping. A dish wears at the place that the tip of the screwdriver is pointing. You get these new in gasket kits.
In the back plastic part if you rotate the two pieces you will notice how the parts cam apart. There is a plastic ramp so that when you pull on the throttle cable it pulls the needle up and lets in more gas. So I try to put some grease on that cam surface before puttign them back together.
In this picture you can clearly see the needle. So when you turn that needle with screwdriver CCW it goes up and lets more gas in. Likewise when you pull on the throttle cable the same thing occurs. These units become sensitive to temp as things wear in. That is the reason you need to be able to make these adjustment.