Bubbles in fuel line?

Anyone know why my fuel pipe on Vespa GT (1969) always has bubbles in it?
It’s causing fuel starvation and won’t go away. When I try letting the fuel flow before connecting to carb banjo there are always bubbles in it. It is fitted with standard pipe clips (new) and 24" (600mm) of fuel pipe.
Tried tightening friction washer screws which bare down on the rubber washer untill I can barely opperate the tap. No luck.
Tried tightening the sediment bowl screw. No luck.
Tried fitting a new tap today… still no joy.
Have I done something wrong??
Can anyone help?

Sorry, but these bubbles are there even when the carb is disconected.

Thanks though.

Sounds like you have a carby problem and not fuel tank problem.

I suggest rebuild your carby which is very easy.
Strip & clean in a good quality carby cleaner and then blow out all channels, holes etc with compressed air.
Use new gaskets and replace your float needle and check your float for leaks „if there’s fuel in it get a new one“

re-tune your carby and you may have the problem fixed.

Hi,

it sounds as a prob with the fuel tab

change it - it is not so expensive

 

greets