From what you describe it sounds like your bottom end might be rich, lean your low end needle 1/16 turn at a time and run your engine, allow it to idle for 10 seconds or so and punch the throttle wide open to see how your transition is. Repeat these steps until you achieve a sound transition. These same steps will work if the mixture is too lean, only richen the low end needle 1/16 turn at a time.

Bob Sawyer