Got my dual Holley 390's (4160) up and running on my little 302, stock fuel pump. Not leaking when the car is running, but a few moments after I shut her down, gas dribbles out of the DS of the front carb at the fuel line tube. The carbs were fully rebuilt less than a month ago, including the fuel line tube O-ring seals. I believe the seals are good, because it doesn't seem to leak when it's running.

I checked the float levels; everything looks kosher. Is this just backpressure? If so, how do I alleviate this?