[bobcowan]

Unless you installed some really cheap or really old rubber hose, that doesn't make sense. E10 has been around for a long time - like 1-2 decades. And yet nobody else has this problem.

You should be able to install one filter near the carb and call it good. You drained the fuel tank, and it was clean. So it must be coming from the lines or the pump.

Remove some of the rubber line and cut it open; see what the inside looks like. Put it in a jar of gasoline for a few days, shake it up every once in a while, and see if it softens up and deteriorates.