Quote Originally Posted by mrmustang View Post
Spray a solution of soapy water at the base of the carb, and around the intake manifold to check for additional leakage.
Bill S.
My first thought too. If you don't find it with the soapy water, how confident are you with your head to intake seal on the bottom side? Did you check the fit of the intake before assembly, assuming that the block was probably trued up to square the surfaces?

On the stumble, have you tried increasing your accelerator pump stroke a bit?