Fuel trouble on a throttle body

1989 nissan sentra 1.6L tbi 2wheel drive manual 213,000miles and just breaking it in. I haven't been able to pass emmissions, which I have narrowed down to a fuel issue. Everything ignitionwise has been replaced. (cap, rotor, plugs, wires, ignition coil) and emmision controls also cat O2 sensor mass airflow. The problem I'm having now is that it is getting too much gas. There is the black soot-like deposit all throughout the exhaust. It's definately not oil, just gas. I've replaced the fuel filter, fuel pump strainer, and rebuilt that one trooper of an injector; which had been previously replaced about three years prior. What I'm mainly concerned about is if there is some way to manually adjust the fuel coming in on this car that I don't know about. Again this is that beautifully dasigned tbi engine that they made for my car for 1 year. Any suggestions would be greatly appreciated.