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Testing different fuel tank venting.
Old method resulted in fuel siphoning out the bottom vent, and blows fuel out the caps (which is really noticable on a polished wing) when the tanks are over half full.
New method adds a top vent (actually a 1/8 NPT elbow for now), and blocks off the pre-existing bottom vent.
Consecutive test flights show the leaks are now stopped at current fuel level, which effectively increases the amount of fuel that can be put into the tanks.
Watching fuel pressure gauge carefully (and logging the data), and getting the same readings as before. Upcoming tests will be with full tanks and extended WOT.