thick black smoke, lack of power, poor acceleration

I have a 1985 F250 6 cylinder with a single barrel carbeurator with 45,000 miles. Now when I start it it runs really rough and coughs out thick black smoke with a really rough idle. Once I get it out on the highway it suffers from poor acceleration and awful fuel economy. I removed the EGR valve and there is no visible carbon build up. I could use any help. Thanks