Big Block Fuel Filter Bubbling Fuel, What The ???

[savatreatabvr]

I've got a 1973 C20 454, this morning I decided to pop the hood just to check things out and when I fired it up the fuel in the clear fuel filter was bubbling. It was running ok so I took it for a 5 mile drive and it was still bubbling and still running fine. I'm assuming I've got air getting into the fuel line or fuel pump some how some where, is this a common thing, has anyone seen this before or does things like this only happen to my truck, lol?