The fuel system can be considered in two parts, fuel supply and fuel delivery with the fuel delivery system being the throttle body and injector. The throttle body and components are largely the same on all the year models. The pdf here has information on part numbers for all year models and variants. Fuel Delivery pdf
There is much discussion about the "mystery connector" on top of the fuel tank. It is the connector for the US only Tank Vent Valve. The pdf here has information on the valve and fault finding. Vent Valve Info pdf
The 00-09 Dash info pdf has information on the fuel lamp operation to assist repairs. 00-09 Dash Info pdf
The resistance of the BMW fuel pump is difficult to measure, readings between 1.5 to 9.0 Ohms may be seen.
Current draw is 2.6 amps @ 12.5 volts with the filter regulator disconnected.
Current draw is 4.6 amps @ 12.5 volts with the filter regulator connected.
The GS911 has diagnostics routines to operate the fuel pump and the fuel injector to aid in fault finding.
Replacement fuel pumps are available from HiFlow, notes on the procedure are here:
Fuel Pump Notes pdf
SFMike at f650.com has done a write up on fitting the Hiflow pump, a pdf is here: Fuel Pump Replacement pdf
A number of owners have reported fuel pump failures. It seems the three supports sag with age leaving the pump supported by the wiring. The power wire to the fuel pump can fracture and fail. The failures have been documented at f650.com and the repair procedure below is from the threads. A pdf of the repair procedure. Repair pdf
Remove the seat, disconnect the plugs to the fuel tank cap.
Unscrew the big plastic ring on the top of the fuel tank.
Pull the pump/gasket out of the tank.
Use a multimeter to check the wiring is connected.
Reconnect wiring & use a length of wire to extend wiring if needed.
Wire colors Red is Power, Brown is Earth
Carefully place the fuel pump into the fuel tank.
Take care with the rubber gasket, it can get caught on the big threaded ring and then does not seal well.
Run a smear of grease between the gasket and the fuel tank plus between the gasket and the ring to ensure it seals.
Reconnect the external connectors to the fuel pump & check the bike starts and runs. Put the seat on, all finished.
Full credit to Workerant and Richard who posted the details of the problem and the repair at f650.com
The seal on the fuel tank locking ring under the seat can perish or not seat correctly and cause fuel leaks.
The Sertao in particular has had problems with the seal and has been subject to warranty remedial action.
Bad connections in the fuel pump connector on top of the fuel tank can melt the plastic and cause fuel leaks. This is a known problem on other types of vehicles with in-tank fuel pumps. Check connections periodically.
The metal neck of the fuel filler can rust, particularly where the machine
has been parked for an extended period. The rust can fall into the bottom
of the fuel tank and clog the filter. Cleaning the tank is then hard.
The Filler Cap screws thread into plastic and brass inserts which can release and spin preventing removal of the filler cap. Once removed by either drilling the head or spinning out by rotating anti clockwise with a drill to generate some heat, they can be epoxied back into place.
The problem of cracking of the top of the fuel pump mounting has been reported on both US and EU fuel tanks. A recall was done on the F650CS models in the US only but not on the GS. The symptoms are fuel odour and fuel leaks when on the side stand. Check the mount during maintenance when the seat is off and if cracks are found replace the assembly. Note. The mount is only available new as part of the complete fuel pump assembly
There are 3 variations on the fuel injector, the basic connection and operation is the same on all the models.
Details of the injectors and the alternatives are in the pdf. Fuel Injector Info pdf
The filters and regulators have been a source of annoyance with owners, on the GS the cost of the combined unit and on the 650X, the lack of BMW part numbers for the filter and regulator. Alternatives to the BMW units are not well documented, what we do know is in the pdf here. Filter Regulator Info pdf
The regulator specification is for between 3.3 and 3.7 bar. This results in significant variations in fuel injector flow rates (341 to 361 cc/min). When replacing a regulator reset BMS adaptions with a GS911 to adjust for the change.
The G650X has a fuel filter system in the fuel tank freeing up space under the cowlings
eliminating the fuel return line. There are no Part No's for the filter/regulator. The F800 also
has the filter in the tank. It may be possible on the 650GS, more investigation is required.