Here's a link about Anti-percolation modification on IDA 3C carbs.
http://forums.pelicanparts.com/porsc...ification.html
The only benefit would be the bowl is directly vented to the throats of the carb, which is technically correct if the carb has individual filter screens or filter socks.
The bowl is normally vented to atmosphere which could be unfiltered air in some installations.
Any carb that is vented only to atmosphere could benefit from this sort of modification.