How much fuel needs to be in the tank to create fuel flow when the tank is in the firewall?

As the fuel outlet is at the bottom of the tank any thing above that.

Likely a pint or so. The sediment bulb outlet is at the base, but in a corner. The tank base is rather flat.

So if the T is on an opposite slant grade, maybe more needed to get to the other side with the outlet.



But safer to say, 1 gallon would assure fuel flow with a running, driving T over roads!

Thanks for the diagrams, Dan. Apparently my fuel flow issue is something else. I think I may just take it all apart and investigate, starting from the bottom up, as the glass bowl is filled with fuel. I suspect a stuck needle valve.