When I built my Four Star, I cut the brass fuel lines too short, so that less than 1/4" of fuel tubing was biting on the brass tubes. I pull tested in the shop and they seemed secure. I even put retainer clips on them. The first time I went to fly it, between the heat and the fuel, the lines slipped off and I couldn't get them to stay on. I ended up pulling out the tank and installing longer brass tubes.