40 is very small for your motor. Des Hammill makes the following recommendations for fuel orifices
40 - 250 to 350 cc/cylinder
45 - 350 to 420 cc/cylinder
50 - 420 to 490 cc/cylinder
55 - 490 to 560 cc/cylinder
Alfa fitted 50F8 in 2L motors and that should be close, even with bigger cams.
50F11 is one step leaner and 50F9 is one step richer. I would be surprised if you had to go outside of that range.
Here is a copy of the Weber tuning manual. http://www.lainefamily.com/images/WeberTuningManual.pdf
You will find dimensioned drawings of all idle jets. It may be possible to drill out an orifice to make a different idle jet if you do not have it on hand.
the list of idle jet air bleed suffixes from rich to lean is F6, F12, F9, F8, F11, F13, F2, F4, F5, F7, F1, F3