What you are describing is what happens when a hole appears in the accelerator pump diaphragm on a Carter YF2100 (I know, nothing like looking at an apple to find out what's wrong with an orange).
I am not familiar enough with the Model B to know if a faulty accelerator pump circuit will also cause your issue.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission