As stated by Joe in the previous post, the "plug" is the main metering jet.

While it is impossible to know what Dr. Goodpliers (the evil twin of Mr. Goodwrench) may have put in any carburetor; Carter built the type W-1 without the use of loose check balls. The inlet and outlet check valves for the accelerator pump are encapsulated balls or wafers. These valves screw into the pump column which connects the accelerator pump well with the pump jet.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop