Low fuel light problems

[Andy FitzGibbon]

My red low fuel light (the one on the right) illuminates in a seemingly random way...including, occasionally, as I'm riding away from just having filled up at the gas station. Ideas?

I've never seen the amber light (the left hand one) illuminate...the bike is an '85 100RS, so it *should* have both lights... but, the previous owner had the cluster replaced at a BMW dealer for a non-working speedometer, so perhaps it has only one now.

Thanks,
Andy

[Laitch]

Ideas?

I'm taking your post as an opportunity to use a descriptor than seems popular with Ozians. Your fuel sensor might be cactus. If it were my bike, I might remove the sensor to have a look at its overall condition and wiring. If that seemed too threatening, I might place a piece of tape over the light in the instrument cluster to mute its effect on me then learn first-hand what my average mileage-range-before-fillup is using my trip meter and a container with a gallon of spare fuel.

[The Mighty Gryphon]

+1 on the tape.  A pinhole will let you know when the light is on, but make it easy to ignore.

Safe range between fillups is about 200 miles; I try to fill at 180.  Use your tripmeter to keep track of fuel supply.  It's what I do to avoid having that low fuel light blinding me at night.

[Andy FitzGibbon]

Yeah, I keep track by mileage too. The light doesn't really bother me that much. I was more looking for advice on fixing it- wondering if there was some common problem I should check first before tearing into it.


Thanks,
Andy

[Brick_hack]

My K1100lt doesn't even seem to light up at all even when the gauge is reading empty and I can't see much gas in the tank. I've never run the bike empty (I don't know if it will overheat the fuel pump), so I don't know if it's actually working or not.

[The Mighty Gryphon]

I usually run my bikes to where there is a bit less than one gallon left in the tank.  I don't worry too much about how submerged the pump is in the fuel.  I figure it's got fuel flowing through it carrying heat away.  On my RT, I have a fuel cooler that keeps the tank a lot cooler even in temperatures above 100F. 

What concerns me is whether or not the pump can cavitate as fuel sloshes around in the tank when the level is low.  That can't be good for it, so I want to refill while there is still about 3-4 liters of fuel left.

[Filmcamera]

My light comes on with between 1/3 and 1/4 of a tank.  One of these days I plan on trying to adjust it.

[Laitch]

The light doesn't really bother me that much. I was more looking for advice on fixing it- wondering if there was some common problem I should check first before tearing into it.

If you have the fuel sensor with the float that is attached to a plate bolted to the bottom of the tank, remove the wires that go to the fuel pump, then pull the sensor through its opening in the bottom of the tank and assess its wiring and it's general condition. Immersion in old ethanol-laced fuel promotes its deterioration. There are aftermarket replacements for that one or you might be able to rehabilitate it. If you have the early sensor that is attached to the bottom of the tank by one fastener, that one isn't reproduced any longer.

This link shows the two types.