This is my husband's write-up since he did all the real "work". I just held stuff out of the way.
There are many many posts on here for fuel light/sensor not working, etc. but none that I could find describing how to actually fix it. Thought this might be useful to some others here:
Kristen's bike (2002 M750S) has been telling her she is out of gas even after filling up, which means a bad fuel level sensor. Prior to not shutting off at all, it would flicker on and off for no apparent reason.
She ordered a new one for $150 (ouch...and this was a discounted price) and we spent the better part of the day today getting the old one out and the new one in to the tank.
The fuel level sensor is number 5 in the below picture.
This was kind of a pain, and still easier to extract than the fuel pump/level sensor on my VFR - I kind of like the way they set it up on the Duc tank.
First step is to drain the tank as low as possible (we unscrewed the sensor part way and situated a funnel where any gas would leak out to drain into a bucket), then make sure you unplug the sensor wire from the bike harness. It is a 4-wire plug. We still had a little fuel leak out onto the rags under the tank when I completely unscrewed the sensor.
You have to remove the gas cap, and then the ring that the gas cap attaches too is held onto the tank by 7 or 8 set screws. We ended up using a 5/64 allen wrench since a 2mm one was too small and the 2.5mm one wouldn't fit.
Once you remove the set screws you can pull the aluminum ring out of the gas tank and set it aside. I wrapped a long screw driver in a towel and used it in the filler neck as a lever to get the ring out. Note that there is an o-ring around it that seals the aluminum ring/tank interface - this is what makes the ring fit tightly. The aluminum ring is shown in the picture above the hole in the tank, that is not the gas cap. We left the hoses connected to the vent hole lines at points A and B and Kristen just held the ring out of the way.
After that it's very easy then to reach down and get to the fuel filter - it's right under the filler neck area. That will be an easy change when the time comes.
In order to get the fuel level sensor out of the bottom of the tank, you have to unplug the fuel pump power wires, which enter the tank through the body of the fuel level sensor. To do this you have to reach your arm down into the tank and pop the fuel pump out of the C-clip holding it to the bottom of the tank. The fuel pump actually has a separate rubber surround which protects it, that is what the c-clip is grabbing. In the parts photo the rubber surround is #1 and the fuel pump is#2. The picture is misleading since it is an exploded view. The fuel pump will be inside the rubber and held in the c-clip.
I pulled upwards on the fuel pump and it popped out of the c-clip very easily. Then I pulled it towards the filler neck hole until the power cable clip could be reached. There is NO way to unclip this plug without pulling it up to the top of the tank, as you have to depress the clip from the side that points towards the bottom of the tank and at the same time pull out the plug. In the picture the plug on the pump is that tab looking piece that points to the top of the tank.
After you unplug the power plug from the fuel pump you can unscrew and remove the fuel level sensor. Make sure your new level sensor has an o-ring. Buy one when you buy the part or if you feel lucky use the old one on the original sensor.
Put the pump power wires into the sensor hole first when putting the new sensor into the bung on the bottom of the tank. Tighten the plastic nut snug enough to prevent leaks, but don't overdo it and strip the plastic nut threads on the metal bung threads!
Now you can reach back into the tank and pull the power wires (black and red) up to the fuel pump and plug it in again. At this point you are ready to begin the epic struggle of getting the fuel pump/rubber grommet back into the c-clip. This took most of the time on reassembly of the fuel system. You have to do it by feel of course since you can't see into the tank with your arm in the way. Actually after I got it lined up properly it went in pretty easily - the trick is that you can't push it in from the front of the C opening, you can to put the pump and grommet at the top of the C (the side of the C) and push down. The rubber surround has a taper to the bottom of it that facilitates this installation method. The hard part was making sure I had it aligned properly in the clip before exerting downward pressure.
After the pump was back in the C-clip you can reinstall the aluminum ring. Oh but before you do make sure the fuel filter is placed back into its clip as well. You might want to have a new o-ring for it in case yours is in sorry condition.
We buttoned everything back up and put in some gas - hoping that the new sensor wouldn't leak. It didn't, and the fuel pump also worked properly.
The next time we have to mess with the fuel system it shouldn't take so long.