Sounds like you need gaskets on both sides of the insulator. Make sure the hole on the bottom of the carb has a passage in the gasket to reach the vacuum in the manifold. Make sure you have the float level set right & the power valve piston goes up & down & kicks the ball off its seat.
Throttle shaft wear on the B carb is seldom a problem. The base is cast iron & both sides have a long bore.
