Weber DCOE / IDF emulsion tube  F2. F9. F11. F16.

F7......... For mixture enrichment at low rpm or during slight accelerations ( no orifices at the top)

F2, F11, F15, F16............ For mixture weakening at low rpm or during slight accelerations (orifices at the top)

F11....... For high rpm mixture richness reduction when air jet is larger than 2.00mm (many orifices)

F2,F3,F4,F7...... For very large main fuel jets or alcohol based fuels.