SU Carb HS2 "Baffle-overflow" (Haynes manual)

[Phil-1954]

All,
The top of the float chamber on my new HS2 carb has been continually stained with brown fuel residue ever since fitting it (40 miles ago), and this is despite trying two different 1/4" new fuel pipes and using the correct fuel clamps (C types, not Jubilee). So I next suspected the brass pipe where it's pushed into the lid's casting was seeping at the joint, and was going to contact ESM and ask them to replace the lid. - that was until I noticed a clip as arrowed in red below. This is given as a 'Baffle-overflow' [27] in the Haynes.

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Does this just cover a breather hole in the casting or is meant as an actual overflow, as by the time the fuel is that high I would expect the engine to have stopped anyway - well on tickover at least!
Original HS2's don't appear to have this clamp.

I'm now wondering if fuel vapour venting out of this so called 'Baffle-overflow' may be responsible, or do the lid's have a tendency to seep around the brass inlet pipe joint in the casting?

[philthehill]

The part in question (No: 27) is only there to cover the float chamber vent and stop dirt getting into the float chamber.
If the vent was not there the fuel in the float chamber would not efficiently pass to the main jet.
If fuel is coming out of the vent the fuel level is either to high or your float needle is not correctly seating allowing fuel past the valve.
Not all HS2 carbs had the 'baffle' though it is better if the baffle is in place.

[Phil-1954]

No Phil, thankfully no fuel coming out. If it's only a breather hole I can't see the vapours being enough to discolour the float bowl lid as much as it does. I suspect it's where the brass inlet pipe is pressed into the lid casting then (that's all that's left).