I seem to have problems installing the fuel level sender, so I though I'd ask if there's a trick to it? I feels like its hanging up on something slightly, but I can't see what.

The fuel gauge has been bouncy, particularly when the car first starts. Going rapidly between 3/4 and 1/2 full or so. After a little bit it will settle out, a week ago it was about 1/2 full, maybe just under. This past Tuesday I went to drive the car and the gauge read empty, then bounced between empty and 1/8. I was already late, so I took a different car and have only just got around to investigating. I measured some resistances and, from what I can find online, the wiring seems fine. So I removed the level sender and had a look. The fuel level is conveniently right up to the bottom of the level sender opening. It didn't leak, but I wouldn't want it any fuller. Putting the sender in, I need to curve it around an opening in a baffle. That goes fine, but it doesn't want to seat against the tank. There's a little springiness that I think is the problem. I can push it and get the sealing ring on, but I don't think its right. Having just messed with it the gauge now reads empty with the light on, so I've definitely done something wrong. But what?

 

Sounds like it’s upside down.

 

It seems to be hanging up on one of the baffles. While inserting it I gave it a bit of a twist, and it is now seated properly against the rubber gasket. But the gauge is still bouncing around. This is, as far as I know, the original sending unit for the car, but it might not be. The float is rectangular in cross section, with small radius corners. All the images I see online have oval section floats. When I try to install the sender, the float insists on being horizontal and I think that's why its hanging up on the baffle. So I guess I need a new sender? The float doesn't seem to be available separately. Maybe I need to do that anyway since I'm pretty sure this started after I replaced the fuel tank a couple of years ago.