The velocity stack may help, but I never have seen much difference, other than keeping the carb from spitting fuel.

If the diaphragm vent hole is into the air stream. Solder a piece of brass tube over the hole. You may have to put a new hole in the plate (center) and seal the other one off.

Attach a piece of fuel tubing to the brass tube, and put the end through the firewall and into the fuse, so it will have undisturbed air.

This picture was not taken for this purpose, but you can see the tube in it.