Very interesting. I've been having a devil of a time with my YS63S. Broken in on 20/20, runs great when first started cold but after 5 - 6 minutes, begins to run eratically, always followed by dead stick landing when throttled down to idle. Tried to adjust with mid-range regulator and idle bleed air needle screw adjustments. Not having much luck. Never gave bubbles in fuel tank any thought. Tettra tank mounted over CG with brass clunk. One fuel and one pressure line with aluminum fuel dots tee'd in. Not enough room for a smaller header tank, so, does YS sell the "special foamie clunk" separately ? Don't want to ship back to YS without trying to solve on my own.

Steve H