If it is a Holley it could be jets, accelerator pump springs, float levels, sticking choke if so equipped, vacuum leak, weak fuel pump delivery pressure, clogged/hampered air cleaner element(the oval Cobra style aren't all that good for air delivery) and a myriad of other ailments.
Can you tell I'm not enamored with the vaunted Holley
I spent close to $150 on rebuild kits, jets, etc. on my Holley--I put the Edlebrock on changed one set of metering rods and my car has never run better.