I owned a highly-modified flathead in a 47 Mercury convertible for 13 years, so the suggestions I'm about to make are from lots of hands-on experience!
First, be sure you don't have any seep leaks in flex lines, fittings, etc. The pump sits about 16" or so above the tank, and that's a long way to lift gasoline. I had a flex line from the body to the pump with a pinhole leak that drove me nuts! It would suck air, but wouldn't leak gas. Look for any flattened spots in the metal line down the frame to the tank, or rusty spots that might let it lose vacuum theough a tiny pinhole. Be SURE the tank pickup is clear. They didn't put a strainer in the tank, just an open tube, and a 2" long grasshopper will fit very nicely into the pickup tube. Don't ask me how I know, but it has something to do with a missing gas cap, and getting parked in a grassy field behind the shop for a while!
Last, and most important- - - -Forget the Ford-manufactured fuel pump, or its clones. Get a Carter pump if you can find one! Lose the electric pump, buy a good Carter mechanical pump, and new flex line, etc. Your fuel-starvation problems will disappear.
Jerry
