The fuel sender that is fitted to the ST range of Ducati motorcycles can be problematic, just try a Google search to see what I mean. After filling the ST2 up with fuel and resetting the trip meter I was stunned to find the low fuel warning light came on at 209 kms and there were no bars showing on the fuel gauge.
The green arrows show the fuel light (off) and the gauge showing all bars (full).
When I filled up at around 215 kms and measured the amount that went in I found that there would have still been at least 9 litres in the tank despite what the indications were telling me! This was something to be investigated as I understand that there is no way to adjust anything on the system.
A few weeks later my wife (BMW F800ST) and me on the Ducati filled up with fuel, my gauges were showing full for about 30 kms then everything went down to empty. I stopped and looked into the tank, it was still full. Off we rode again, the light went off and the gauge showed a quarter full for 10 minutes and then went back to zero. Time to investigate.
The first thing that I did was to get a large spanner and tap the fuel level sender in the tank (shown in the next picture) to see if anything would happen, nothing did.
Time to start draining the tank to look at the sender. I had an empty 20 litre can which was just big enough. The tank was emptied, removed from the bike and placed upside down on a blanket to get access to the inside. Three nuts were removed which allowed the fuel pump assembly to come out of the bottom, and then the sender was pulled out. It is only fitted in with rubber cups top and bottom (shown in green in the picture below) . When out the sender (shown in red in the picture below) could be tilted up and down and a float of some sort could be heard going from one end to the other.
It looks like it should not be dismantled and there is no obvious way into the sender so I left it as it was. I decided to adjust the position of the sender just in case it was working again, so that the light would come on with less than 9 litres left.
Both the rubber cups (green) are the same and they both have step inside them to stop the sender sliding up and down when in position. I cut the step and the bottom of of one of the cups and fitted that cup to the bottom of the sender so that it sits about 15 to 20 mm lower in the tank. The sender was refitted in the new position and the fuel pump and tank were all fitted back to the bike.
The tank is now full, as the pictures show, and everything seems to be indicating as it should. Perhaps something was sticking and has been freed up by my playing, but we shall see. I will run the bike till the low fuel light comes on and report back on the new position of the sender unit.