76 gmc sierra probs

Ok im having a problem with my truck

it is shooting out black smoke. like when i start in the morning and let it sit for like 10 mins running, i come out again and its "sputtting" black smoke and it sounds like its gonna stall, never does though. When i go to give it some more gas to stop the sputting a big puff of black will come out when i rev it. I would like to know what might be causing this.

If anyone has "ANY" suggestions i will take them into consideration.

wow so many helpful replies

thanks guys.......... :(

Black smoke could mean it's running too rich. There are a lot of possible reason's for this including a stuck choke, incorrect timing, or clogged air filter. On a 76, I'd start with the air filter and then choke.

Ya sounds like a stuck choke

ok i shall start with air filter

thanks for the help