Ignore it and ride it. There will be no stumbling, coughing, stalling or hesitation. I imagine this 'bubble' forms in most if not all fuel lines at some point, but most fuel lines are black, rubber and therefore can't be seen. The bubble you see does not impede fuel flow; the fuel simply flows around it, and at some point the bubble will slowly migrate to the fuel/carb bowl, quickly followed by more fuel. I have run this set-up for over a year and a half, and have never had a fuel starvation issue even at extended freeway trips at or over 75mph.