How do I adjust carb chock on 78 chev pu

The choke should have a housing with maybe three screws holding the cover on. I think all you do is loosen the screws and rotate the housing so that the choke butterfly is closed when the engine is cold. Tighten the screws when you are done.

if it starts fine first thing and when you hit gas it idles down then choke it fine carb is flooding your float is set to high, or it keeps dripping into the intake, with key off hold gas to floor to let gas evaporate for atleast a min or more then try. after you turn truck off and walk away for 3 to 5 mins open up air filter and see if you smell gas,depends if you have rochester carb might need to get carb kit and fix it, or just tighten up carb bolts just a little thet get loose after so many years dont torch just tighten