2.0 with dual carbs

[fiat218]

what is this brass tube for ?

[fiat218]

here what they are

The brass tubes on your IDF rather belong to a full throttle enrichment system, and are a feature solely found on the 40 IDF 13/15 type (These carbs were stock parts of FIAT Spyder's 1600cc engine back in the 60's). The tubes are meant to work together with the cylindrical velocity stacks that bolt onto the carbs. The principle is very simple: the brass tubes are directly linked to the float bowls. When the engine is operating at WOT, a certain pressure drop compared to the surrounding atmosphere pressure is developing in the velocity stacks. This causes the fuel out of the bowl to be drawn upwards through the tubes and being sprayed into the intake air, thereby enrichening the mixture.