32 model B - Will not start

[greyhound]

I am looking for some advice. I have a 32 model b and it does not seem to draw fuel/air mixture from the carb through the intake. I removed the intake and it isn't blocked and there aren't any obvious areas where the may be a leak. Carb and fuel pump have been rebuilt, and there is good spark at all 4 plugs. Any ideas? Many thanks in advance.