hpergm

The idea is for the carb to breathe within a plenum where pressure differences are not really that pronounced; this means a volume with dimensions much larger than the trumpet's bore and as much separated as possible from openings that create negative pressures (louvres) @ speed. Ideally, then, the carb should breathe through the fuz - which, in turn, should have some air pressure "relief" holes (i.e. openings parallel to the flow direction, ideally at the bottom and/or sides) to maintain an even atmospheric pressure at any speed.

What I did in practice: my FG-60carb was just 1cm from the face of the firewall, a distance dictated by the length of the stand offs I used (had to be longer than Saito's). This would give rise to uneven flow, since the ~1cm distance is comparable to the trumpet's diameter plus it would only breath through the cowl's volume the pressure in which is strognly affected by speed (I also got louvres). So, I opened up a hole (28mm) in the firewall right opposite and then used a sort of "sleeve" to take up the distance, so that the trumpet could breathe "cleaner" air from within the fuz plenum. As it happened, I had measured several plastic cups from... toiletries' bottles until I found a plastic dosing cap from a medicine bottle to be a perfect fit. Photos below tell the story..