‘77 xs650, when i bought it it would fire up on starting fluid. I cleaned out the tank and carbs but when cranking I can see the lines from gas tank to carb is empty. I think the petcocks are clogged up so I’ll clean those out, but the fuel lines are not vacuuming and I believe 77 need the vacuum to suck gas right? If you do need the vacuum then what could be causing it not to?