Having that vacuum tapping on the carburetor work properly matters, Jaffa, but it wasn't the issue that prevents it from starting when you put the top on the air cleaner box. It's a basic rule of scientific investigation: cause and effect. If you put the top on the air cleaner, it won't start. If you take the top off, it will. You have repeated that experiment at least twice, and got exactly the same result each time. Therefore you only need to look at things that are different when the top is put on the air cleaner box.
