[SBSerpent]

"then it means either your needle and seat is leaking or your floats are too high or the gas you are using is really $hitty and is percolating up and out through the boosters"

...or the O-ring on the N&S assembly may be leaking?

I experienced exactly what you described in your write-up but in my case, it was on a cold start (car hadn't been run in days), which takes the percolating gas factor out of the equation.