I'll assume you have a Carter BBD carburetor which is common on those.
Check to see that the choke pull off is operating and the choke is set properly. Should work like this-- cold. Press down accelerator choke snaps shut, engine starts and pull off pulls choke open 1/4". If it operates in this fashion but is still "chugging" open choke a bit more with a screwdriver. The stroke of the pull off is adjusted by pinching the linkage to make it shorter if need be. That is one of the most common rough idle and black smoke problems. As it warms up the choke should open fully.
http://www.carburetor.ca/carbs/kits/CK021.htm