Edelbrock mid throttle problem

Thanks for tips! Today I continued tuning by changing primary jets and metering rods back and forth. I also changed stiffer springs. I double checked the ignition timing and it is 14 initial and 37 total advance. Total advance occurs after 2500rpm. None of these settings changed the problem. I have used edelbrock carb tuning jet kit.

This problem is easy to notice, because when I am accelerating by using second gear only, engine first feels strong but then it takes time before you reach around 75% of the power, it really performs very well!!!