Don't use 'full swing' when checking the range on the hangar. Odds are it's greater than the actual height of the tank (both top and bottom).
Also, keep in mind, the float is about 1" around so it hits the roof before the fuel level gets to the top of the tank, so it's going to top out while you've still got a couple gallons left to go. That's the reason cars always seem to stay on full for so long then drop like a rock.
Edit: I just remembered my precision depth transfer tool(AKA Home Depot paint stick) was still on the hood of my TVR... My original tank was 8-3/8" deep to the baffle and my brand new Spectra tank is 7-7/8" deep.
Years ago, when I measured that while replacing my fuel pump, I ended up modifying the hanger base to let the pump sit lower. As best as I remember that extra 1/2" netted me something like 1.85 more gallons I had access to.
Also, since it appears that attachments work now, do this to the hangar and the fuel gauge will be so responsive that you can actually see fuel slosh on the dash.
OK, they still don't work. Basically solder a wire from the hanger tube ground to the float arm. Do it in a decent sized loop so that the float can't break the wire over time from actuating.
Odds are it'll change the impendance reading of the output. If you look at the design of the gauge circuit, it's utter shit and I have no idea how it even works in the first place. The ground for the reostat comes from the area the float arm passes though the metal holes on the thin casing that's mearly crimped lightly in four spots.
By giving the float arm and actual ground, the curcuit can actually do it's job.
