Fuel will not equalize when driving

There is vents on top of your tanks, usually they have i little lose running down the tanks on the outside. I would check and clean/replace those before i do anything else. Is they are dirty it will cause vacuum in the tanks.

 

Sure sounds like a dirty dober done clogged one of the vent lines off the top of fuel tank.

 

On a 2004 t600 and my current 2015 t 680 I run into the same issue .. after changing numerous parts on the t600 I figured out its temperature related and just dump a bottle of conditioner in tanks .. it solves the issue for a month or two and I repeat the process .. I think it's moisture related .. You may want to try this first before going through the parts changing procedure

 

There should be a little canister type filter at the end of each of the breather tubes 20$ or so. Change em both or pull em off and see if your tanks equalize.

My lines were clear however I found if there wasnt equal restriction between the 2 filters, it would throw it all out of wack

 

I'l try to take a pic tomorrow. Mine is a '14 (Im assuming it's the same)

The breather hose should run from that brass fitting, down around the tank and into a little white plastic filter (the size of a mini pop can, shielded with a bent piece of tin held by 2 or 4 little bolts) on the lower inside of one of the tank straps