If you are running a 2 line system you can have a few bubbles after a refuel. This will cause a little hesitation untill the line is full of juice. I also have this problem on my QQ yak with a 2 line , I can see the bubbles through the clear canopy. I also have a WH with a DA fiddy , this has a 3 line, never have a bubbly fuel line.

If you have some pops while flying dont be scart, twist the neddles . Little at a time.

Have fun, Kent