Hi, welcome to the forum. I second the idea of bubbles in the fuel lines. You can see them streaming through the whitish looking plastic fuel lines. If the lines are older, they may be dark brown and you can hold a flashlight behind them to see through.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250