I picked up an old book by John Passini on Weber Carburetors that gives the most comprehensive analysis of emulsion tubes relative to theory and practise. I am not sure I understand it all but if anyone would like a copy, email me @
dhampton@rwbaird.com and give me your fax and I will try and get one out. Etubes are the mysterious part of the Weber carb and this chapter may help clarify some of the issues surrounding them. Interesting reading, in any event