I has Webra T-4 with Dynamix carburator, the milled slot are placed to the hole who are entered in to the intake bore.

To test the mixture tube works: connect the silicone tube to carburator and blow through the milled slot with your mouth. If you feel the passage are more tight while the carburator are in idling position and vice versa means the mixture tube are in correct position.
If not, rotate the pin with milled slot to align with the hole who are in connection with intake bore.