I ran across this picture looking for something else.
Several years back, I bought a 4100 carburetor from somebody (e-bay, swap meet ?). It was missing two vent tubes. I found some brass tubing the right diameter and wall thickness (0.219 in dia, 0.012 in wall thickness) and removed another vent tube to get the length. Using a Dremel tool saw, I cut several pieces to length and cut a slit in each for installation. Use a piece of wood on top of the tube and a small hammer, tap gently for instalation.
There are 4 required on a 4100, 2 each on a 2100 carburetor. These tubes are not serviced but are a part of the top cover (9524).
I got my tubes at a local hobby shop. It may be available on Amazon or e-bay.
Jim