Easy fix -> Don't buy translucent fuel line!!!
[The pressure line feeds into the tank at the top and the fuel to carby is drawn from the bottom of the tank. For bubbles to form in the fuel inlet tube it has to come from the tank feed, nipple and tubing... Or.... it's a hot carby!!? If the bottom mix is too lean and the carby heats up to beyond that of the boiling point of methanol 65c (
https://www.google.com.au/webhp?sour...nt+of+methanol ) then it could be a backwash of boiling fuel. Since methanol evaporating in the carb will cool it down, try a richer bottom and/or top.
Also something to consider is siphon, as there's not exhaust pressure either the tank may cool and shrink but hey, if it's happy and you're happy a few bubbles wont hurt it, unless there's an air leak and there'd be fuel residue there too.]