Gas Dribble from vent

Anyone having seepage from their gas cap vent? The one on their bike, that is.
The cap vent is a copper tube curled in a spiral 4 3-4 times
It's clear when I blow through it, and dripples gas at odd times when riding.
The tank is not completely full. Motor's a four stroke (Honda clone), 49 cc with a stainless tank under the bar (typical boardtrack configuration).
Also, I notice that sometimes there are air bubbles in the fuel line.
Revs seem to surge and then slow at idle...and when riding...with occasional stalls when braking the bike.
Thanks, in advance.....

 

Thanks for the reassurance and advice.
I have a curly-Q copper tube on it....but maybe I'll carry a short length of extra tubing to divert the drips when the tank is full.