Check for fungus in tank by seeing if hand pump creates a vacuum.
84 w123 300 turboD
my inherited car has that symptoms, it did ran and stopped, now i reversed the supply & return steel line the vacuum feeling is gone , is running now , but what should be the real solution?
and some say if it tank is 1/4 empty then it will suck in air and no go too.
since the return line is about 1/4 from bottom, whereas supply line is right at the bottom. regardless is never a good idea to run her < 1/2 tank.
TIA.

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