When you put the carb back on the engine did you put a gasket between it and the intake? There is a little vacuum passage drilled into the base of the carb that needs to see clear into the intake. A lot of the gaskets in the kits don't include a notch. This keeps the power valve circuit from operating in the carb and causes extremely rich off-idle mixture. If you have a phenolic spacer on the intake you can run the carb with no gasket, or just make sure you cut out the notch with a utility knife.
