I need to make a reducer for my Weber Carb Synchroniser / Meter which has a 40mm cone nozzle - I really need 35mm to fit my trumpets properly so a reducer of some sort is required. I was thinking that a flexible rubber cone or funnel would do the trick. The cone could just be held in place by hand over the trumpet and then the Weber Meter (with existing nozzle) pressed against it to take an airflow reading.

Any ideas where to look for said cone guys?

plastic funnel with the end cut off should do it

I have already tried a plastic one but it leaks too much air so I thought something more flexible was in order.