RE: DC2/GT5/C5/FG/EVO/ELCON/CAD/BEETLE
DC: the walbro 771 carb has the same internals for fuel flow as the 813..just no pump..
and I thought you did say air bubbles from the tank...That there says a line pin hole...
but the klunker could be clogged a bit forcing a suck action from the attached line at the barb connection...
For now DC go with the stock carb..& rest of new stuff..too see if you get this sorted out....
All just my opinion...Slawhammer