[tubman]

Whenever I've had this problem, it was usually the power valve leaking. These days, when I change one, I set the carburetor (without it's top) on a pad of paper towels in a metal pan and fill the bowl with gas. When you come back the next morning, you'll know if it's done right. Power valves for Holley 4-BBLs will screw into the Ford carb, but generally won't seal right; it's a common problem.