GAV question-28 Roadster truck

[Bob from Northport]

We have a 28 Roadster truck in the shop with a fresh rebuilt engine. We have gone through the carburetor several times. Truck runs great, idles great, engine sounds good at full retard on spark. It does not start as quickly as I would like. If you touch the GAV and open it at all, the carburetor will flood. When driving, if the GAV is opened, there is a decrease in performance/power. Every other vehicle we have worked on starts very fast with the engine hardly rolling over. Any suggestions as to how to improve this starting??