Do you have a pin guage set or a set of numbered drill bits and a dial caliper? If so, you can gently insert the guages or bits into the air bleeds that are already there (there are some in there I'm assuming) and then measure to see what size they are. The outside ones will be for the idle circuit and the ones closest to the squirter nozzles will be for the mains. All of the outside ones should be the same size, and the inside ones should be the same size as well, but smaller than the outsides. What model of carb is this?