Nissan Repair: Wont Idle down, ball point pen, nissan pickup

Question
I am working on a 85' Nissan pickup. It came in Idling at 3000 rpm, I found a lot of vacume leaks and I have it down to 1500 rpm. I can't seem to get it to idle to 800 rpm were it is supposed to be. Has a rebuilt carb on it that the customer bought. A12 I think. Lots of black soot coming out tail pipe, I believe I have carb problems, This is with the choke off

Answer
Mitch,

There is an electric power valve, looks sort of like a brass ball point pen, with wires hanging out of it.  This is most probably stuck and needs to be replaced.  If it is not the power valve then the float is sinking in the bowl causing an over rich condition.  Most of the time it is the power valve.