Given the long time it has sat, and the quality of "fuel" we have masquerading as gasoline, I'd guess that the internal passages and/or jets are clogged. Best answer is rebuild the carbs. But as a quick check remove the jets and check for blockages and clean. I don't know Solexes so don't know if the jets are easily accessible, but that would be my next step.
You have fuel all the way to the float bowls, thus the problem is downstream from there. Gordon Raymond has posted in the past on filling the bowls with carb cleaner and letting them sit overnight to partially clean the carbs in situ. Please don't take these comments as instructions for the procedure, but search for his post.
Good luck and HTH,
Gone but not forgotten: 70 GTV, 76 Alfetta, 82 GTV6 Balocco, Step front GTV race car. Current: Giulia Spider Veloce race car, 105.51 GTV race car to be.