[Eljaro]

ENTDOC
The F16 tube is common usage and will not lean your low end. You will still have too rich a transition.
The higher the holes on the emulsion tube the leaner the low end gets, which is what you want to achieve. The F7 tube commonly used is for a rich transition and the main problem in that area. That is why you have the black sparkplugs and that is the reason for the stumble: too much gasoline.
I simulated the F2,F3,F14 and F15 tubes which are all supposed to be for a leaner low end.I used several different sleeves with variable holes and the best results were achieved with the F14 tubes. This of course in combination with smaller air correctors i.e. 120.

I would like to see someone trying this out (in combination with larger chokes on a BB)and posting his results. This could come confirm my findings and make weber tuning less misterious for everybody.