Gordon, some good help and some not. Webers should be 3 to 3.5 psi, just like Dells. Solexes want 1.5 psi. Dell stuff(especially accelerator jet sizes and emulsion tubes) doesn't help this guy tune, he's got Webers.
I agree that 32 vents are the correct size for a 1915 with 40 x 35 heads. Before anything else, put the 32 vents in.
Then get the idle jets right. 80% of drivability is idle jets. Then get the mains correct. After that, you can play with air correctors and finally emulsion tubes. You can really fine tune with 1 mm of float height in transition too.
And BEFORE you do any of this: ice cold valve adjustment, clean plugs gapped correctly, and rest of ignition system checked and timing correct. Don't forget fuel pressure, no more than 3.5 psi running.