My car with a 6.5 went rich right off idle on the Air fuel ratio gauges. I put a 3.5 in and it was good. I am going to a 2.5 . I don't care what others have to say. I see it with my own eyes.
I can't post a link to a thread (because I don't know how with this dam iPad...I may have to go to the mothership and have them show me how to do it) but I said if you google Mark Whitner he has a video on you tube to prove it to you.
Mark Whitner is one of the best carb guys in the country. He proves the power valve has no affect at idle.