If it still has the factory sock filter on the sending unit in the tank, take it out and remove the sock filter. One filter up by the carb is plenty.

For testing purposes, get one of those clear glass filters so you can see what it's doing. If it's filling w/ rust, you know you need to replace lines and/or the tank. When it starts acting up, you can also see if the filter is full of fuel or if it is pumping bubbles.

Definitely replace all rubber fuel line like the others suggested.