When I read "clear fuel lines" I thought "Uh-oh". Everything I have ever read about diesels warn against using the clear ones. Something about needing to be rated for diesel fuel. Little bubbles turn into big bubbles in places. If you're having problems running diesel, but not VO, then it might be your diesel lines (diesel half of the system, not what they share).

BTW, my 617 primer pump sends the air back to the tank via the fuel return line, so cracking lines is not necessary.