Engine died down at high RPM.

[tsubaki]

If you're sure there aren't any loose connections between the tank and the point where you're getting the bubbles, remove the hose at the tank and try the same thing at the fitting at the tank.
Useing the clear hose helps a lot.
I'm sure this is going to involve removing a floor hatch and a lot of other crap.
Try everything else first, replacing filters, checking for loose connections (there should be a gas leak)
If you have to access the tank, might as well inspect the fitting and tube by removing it. Last resort.