Edited to say this only applies to the 152G model weber carb with the 4 progression holes.
Assuming you have the Weber 45 152G model and the correct idle jet, emulsion tube etc. etc then the sequence of setting the idle should be :
1) Disconnect the throttle linkages from the carbies so you can accurately set the position of each carbies throttle plate via the idle speed screw
2) Remove one of the screws covering the progression holes on each carby
3) On each carby, adjust the idle speed screw so that the edge of the throttle plate is covering the first progression hole
4) Replace the progression hole plate screws
5) Gently screw in the idle mixture screws until you feel them "tighten" and then screw each one out 2 turns
6) You can now reattach the throttle linkages making sure that when you do they do not move the position of the throttle plate previously set.
7) With things now set up check that if you depress the accelerator pedal it does not try to move the throttle plate beyond the maximum opening (adjust the bolt under the accelerator pedal to limit the travel of the pedal).
8 ) Now try to start the engine (after fully depressing the accelerator pedal 3 times)