What is "quite a while"? If you blow air into the fuel return line (at the engine) does it bubble in the tank or just build pressure?

The benz I just got (sat for 2 years with half a tank of gas) required a new in-tank strainer as the old one would barely pass 1 cup/minute, and the in-tank fuel return check valve cleaned. It got plenty of gas, but since the check valve was frozen shut, it had nowhere to go.

I would do the pump volume test to make sure you're getting adequate gas out of the tank.

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.