It has taken some time, but I finally tracked down a fuel leak from the sender unit underneath the left side ( as if you were sitting on the bike.) A very slow leak is coming through the plastic connector that is attached to the bottom of the tank. If you disconnect the wiring plug, fuel comes out the plastic plug, tank side. It isn't much and seems to be nastier when the bike is on the side stand. Any suggestions? I don't really need the sensor as the fuel lights stopped working about 10 years ago and I manage without. The smell is more of a concern and whether it will get worse or let go all together. Any help would be appreciated. The tank is original on 10/83 K100 and has the 4 and 7 litre warning lights (which don't warn any more).

You may not need the fuel lights, but you do need the fuel pump which is powered through the same plug. Any second hand sensors in the wreakers near by?

oh ! ...so the early ones supply fuel power and sensor ....from the front/left hand side of the tank ?



if it was just the sensor ...a bung would fill the bill ?

I may be wrong but I recall the pump wires coming out of the top of the sensor inside the tank. The only other conections to the tank are fuel and vent lines, no other wiring connections. I do recall somebody on this group fitting an external fuel pump, which would allow the sensor being blanked off, but repairing the existing setup would be cheaper I suspect

I have tried Munich Motorcyles in Perth and they don't have any left. They do tell me that BMW still have active part number, there is a gasket as well as the sender unit. Some wire/s then connect from the sender unit to the pump. I am not sure whether the gasket will fix it or I have to get the whole unit. This tank was out for only two years and therefore not many second hand parts and I wonder how good they would be. So just blocking off may not be the solution.

if the genuine gasket isn`t avaiable, I would have tried to find a o-ring in the correct dimension and material.

You could get it from US, but it would be kind of expensive.
Engeland Moto
BMW Chattanooga

Inge K.

The leak may be from the O-ring. They get hard after a while and leak. I had this problem a few months ago and replacing the O-ring solved all leaking problems.

Go and see Pirtek the hydraulic hose dudes they have every sort of O ring and cheap too, and fuel safe.
RT

Just got hold of a NEW gasket from BMW for $10 and have sourced a second hand sender unit for $80 which should arrive this week. This way I will have both bases covered when I pull everything apart. I have been caught before by dismantling something, finding I can't get a replacement and then realising that I can't put the original item back in because I have dislodged something or an o ring is now out of shape.

In this process I have found that there is a massive difference between a technician and mechanic. The technician will only talk about computer linked problems and straight out replacements, whereas the old fashion mechanic has the concept that items can be repaired and there are different ways of tackling a problem.

Thanks to all who have answered my questions.

A few comments if I may. Don't worry when the second hand sender unit's wiring is not the same colour as your own unit's. I got a bit of a shock when the colours were completely different. There is a large and small nut and bolt on the fuel pump, so there is only one way that both wires can be attatched.

Secondly, the small nut on the fuel pump wire is very small and very easy to drop into the tank, not once but three bloody times. To get it out, turning the tank upside down may not get it out. Your tongue must be at a certain angle in your mouth as well as being able to swear in a number of languages may help.

The fuel was leaking through the wiring loom itself. The orange sealing compound that covers the wires in the plastic circular plug had separated at the plastic shell and fuel weeped through that and into the wiring plug supplying power.

Add a new gasket and the job was finished. Beware of small nuts.