I am not familiar with your carb, I did not realize you had a traditional "choke" which blocks the air intake.
Let me try a 2 cent lesson on carburetors and see if you can figure it out.
The float bowl simply provides a fixed level of gasoline for the carb to operate on.
The venturi and slide, the part where the air flows through into the engine, controls the volume of mixture fed to the engine and so the engine power output.
Some carburetors have a tapered needle which fits into the center of the slide and is withdrawn from a needle jet as the slide is raised. If you have one of these, its purpose is to control the flow of fuel from the main jet during partial throttle openings or mid-range. The needle can usually be raised or lowered to vary this mixture by moving a clip which fits in a series of notches in the top of the needle. Many ped carbs do not have this needle.
The brass tube you see, in the center of the venturi directly below the center of the slide, is the main gasoline supply which flows from the main jet, screwed into the bottom of this tube. The tube is sealed to the carb body at the top and bottom and there is a cavity around it between these seals. Air enters this cavity through a passage from the carb air intake side, then through holes drilled in the side of the brass tube. This air is mixed with the gas flowing through the main jet to form a "bubbly" mixture of gas and air which is much easier to vaporize than pure gasoline. This air intake may be what your choke plate is covering as that would make the mixture richer. Old carburetors with a manual mixture control, did so by varying this air flow.
At idle, with the slide in its lowest position, the idle adjustment screw raises the slide to allow just enough air for idling. The fuel for idling is provided in several ways depending on the carb, but they all achieve the same thing. Some carbs have a separate small air intake passage on the intake side of the carb which continues through a smaller passage to the engine side of the venturi. A side drilling provides gas either directly from the float bowl or from the cavity around the center brass tube. The gas supply is regulated by either a removable jet or a precision drilled hole to control the gas/air mixture. Large carbs provide a tapered screw to adjust the idle mixture by controlling the volume of idle air, or of the air/fuel mix. Most ped carbs don't have this.
Some ped carbs get idle fuel/air mix directly from the main jet. When the slide is in the idle position, a channel cast into the bottom of the slide, exposes the top of the brass tube to intake vacuum. This causes the fuel level in the brass tube to rise until the small air flow through this channel can pick it up. I have no proof of this, but I think that the higher fuel level in the brass tube helps overcome a "leaning out" condition as the throttle is opened.
As the slide is raised from idle, the idle passageways begin to lose ther effectiveness and the center brass tube is exposed to the air flow through the venturi. The faster air flows, the lower the pressure of the air. This low pressure above the brass tube allows the aerated gas to flow out of the top of the tube, propelled by atmospheric pressure in the float bowl. The cutaway or angle on the intake side of the slide, controls the speed of the air over the tube at small throttle openings which varies the gas/air mix. As the slide is raised, the cutaway hass less infuence on the mixture and at full throttle, only the main jet controls gas flow.
Cold starting mechanisms are of two basic types, the "shutter over the air intake" type and the "auxilliary carb" type. This type has an extra drilling in the engine side of the venturi, connected to an atmospheric air supply with a connection to the gas in the float bowl somewhere along its length. In operation, the air drawn through the air passage lowers the pressure at the fuel connection, just as the main body of the carb functions, except that the resulting air/fuel mix is very rich. This device is usually controlled by a brass slug which blocks the air and sometimes fuel passages.
A lot of older carbs had a "Tickler", this was a button on top of the carb bowl that allowed you to sink the float and flood the carb for starting.
OK, so my 2 cent lesson became a 25 cent lesson, hope it helps,