Please help! Trans Am with a 455 big block. It has twin 750 carbs and it wont stay running in my driveway when i crank it. i dont know why

. Any ideas? Also think I overpaid. Just took it 150 miles too.
Think i just made the biggest mistake of my life! Paid $4000 for a 1980 Trans Am with a built 455. Has hot intake, bored .060 over, has a new distributor and alternator straps, dual 750 carbs, new rockers, valve job, and rings. TH350 AUTO. Interior needs stereo system and new seat cover as well as seat belts that work. Power Disc front. 3.23 posi. No rust. good glass and lights. Hood is tricky to open.