Depending on the cam in the 307, a four barrel may STILL be to much for the digestion of fuel.

Bill - Somthing that I havn't seen discused yet is ignition timming. If your timming is not set correctly it can cause serious hesitation issues. Also don't assume your harmonic balancer timming marks are correct. Dampners go bad and the outer rings can move causing fales readings of timming. I have repaired many a big block and small block for this issue over the last 40 years. You also didn't mention what size of cfm Holley your running. A 307 cu. in. Chevy usally will be quit happy with a 650 cfm carb. on a street driven vehicle. To large a cfm carb. can cause tunning issues.

Bill - Somthing that I havn't seen discused yet is ignition timming. If your timming is not set correctly it can cause serious hesitation issues. Also don't assume your harmonic balancer timming marks are correct. Dampners go bad and the outer rings can move causing fales readings of timming. I have repaired many a big block and small block for this issue over the last 40 years. You also didn't mention what size of cfm Holley your running. A 307 cu. in. Chevy usally will be quit happy with a 650 cfm carb. on a street driven vehicle. Too large a cfm carb. can cause tunning issues.