If that one length of fuel line isn't rated for ethanlo fuel, that very well could be the problem...I was by my shop here one day and the tech showed me some old fuel line...split down one side, easy to spread apart, the inside of the hose looked like gator skin and crumbled when touched...those small pieces of crumbling rubber were going straight into the carbs...the rubber compound was not formulated for alcohol, only gasoline...replacing that line should be relatively easy to do...I would follow that advise next...

Reel, if that was grey line, it was actually an early attempt at alcohol resistant line, little did they know it would cause more problems than it fixed. I have yet to find a fuel line that I really like, some seem to hold up but are very limp and kink easy, A! type line does well but if its outside where the sen hits it, it breaks down quick, I've replaced more fuel line in the past 5 years than I have in the previous 15