GeneHinshaw, You must have run the fuel low and one of the pickup tubes go air in it. They would not siphon as the air prevented that. The tanks will pull from both on the Right setting, though if they are run down they will not siphon while sitting. If you have a half tank, and top one off, they should equalize over time. The newer 2009 to 2011 models have anti siphon pickups and will not siphon between rear tanks. Better keep enough fuel in those and you run them down before you fill up. Leave a little in the belly tanks for support also. BCB