If this E350 is plumbed like ours was, full pressure doesn't really reach the Float Needle in the Carburetor. The Supply and Return Lines meet at a fitting right at the Carb. It's a "Y" where Supply, Return, and Carb Feed all come together. Fitting is supposed to restrict Return enough that Carb gets what it needs but the system is never totally shut off when the Float Needle is closed.
I've mentioned in other correspondence that Dealers and many Shops want to replace the entire "Pump and Sender Assembly" NOT just the "Pump Kit." This case is an example of WHY. Sometimes the extra expense and shop profit actually work in the owner's favor.
