It looks like you're missing the fast idle link between the choke linkage and the throttle. There's a picture of that link in the 1948-1951 Truck shop manual on page 6-60, although it looks a little different than yours. There should be some kind of link or rod between choke and throttle mechanism.
A PM to carbking here would probably sort out your issue. As his username says, he's the carburetor expert.
