Originally Posted by BFlinn181
When the engine shuts down, have you checked to see if fuel is present in the carb? Sounds like the tank selector valve isn't opening for the main tank. Pull the fuel line off the carb and put the end in a container and see if fuel flows on the main tank setting.
I would do exactly as BFlinn said, and obviously if there is no fuel flow fromt the main tank you have an obstruction
How far from the aux tank is the main tank, maybe the electrical fuel pump can not pull that far.
Reread your post and saw that you replaced your selector valve...also line could be clogged or collapsing or line could have a hole so its sucking air.