Model b carb

[DMontague]

Gentlemen,
I just rebuilt the engine in my 28 AA. It's a diamond block, bored .020 over, touring grind cam, crank grind and all new bearings. I also installed a 6:1 snyders head. When I got the truck it had a model b carb on it. The only way I can get it to run decent is with the gav at least a full turn open. It's my understanding that you shouldn't have to run a model b open?
Thank you!