I have a 1985 Buick Regal. 3.8 carbed. When it is first started it idles high and blows black/grey smoke. Running extremely rich and gets terrible gas mileage. Since it's not a turbo engine I have no idea where to start. After it warms up it still idles a little high but the smoke clears up. I know it's a fueling issue but not sure what. Thanks for any advice.