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Discussion Starter · #1 ·
Hi everyone! I've had a look on the forum but couldn't find the information I was needing, and would love some help!

When I fill the tank up, the fuel light is off, but have noticed it turns on (and remains on) at approx half a tank of fuel. The fuel gauge/needle reads accurately, but I'd love to remedy this pesky light. Thanks in advance for your suggestions/fixes!

 

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Hmmm ... I had a look into how the low fuel sensor works.

It is a separate sensor than the float resister used to drive the fuel gauge. Its basically a thermistor - its resistance decreases as it gets warmer. When its covered in fuel, the fuel sucks away its heat so the sensor stays at high resistance, so it doesn't pass much current, so the fuel light which is in circuit with it hardly glows at all - not enough to be visible. When fuel level drops below the sensor position, the air around it doesn't conduct away heat as well so the sensor slowly heats up due to the current flowing through it, which reduces its resistance which increases its current which reduces its resistance and so on ... as the current increases, the fuel light glows brighter until its visible. This of course happens to a current limit, otherwise it would get so hot it would ignite the fuel vapour in the tank and its game over!.

The thermistor is mounted inside a can which has only small holes in it, such that the thermistor response is slowed and the light doesn't go on/off constantly when the fuel level is near the sensor level.

In your case, I'm thinking the sensor has moved and is positioned too high in the tank so its coming on earlier than expected. I've never actually looked inside my ('97) tank, but I assume there is some type of bracket the sensor is attached to? Maybe yours has come loose or is just sitting too high?
 

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I just had a look on ebay at the fuel level sensor, and it looks like the thermister is on a separate long coat hanger looking wire.

Has this only just started to happen with the low level fuel light? Or has it always done it?.
Have you had the fuel level sensor unit out recently for what ever reason?.
If the wire hasn't been bent by accident, then it could be like leighb suggested, the thermister had moved slightly on the wire.
If you took the fuel level unit out, you mite see if its moved on the wire, after all it's been in 1 place for a fair few years.
 

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Discussion Starter · #5 ·
Thanks for the advice guys, much appreciated!

I bought the bike late last year and it's hardly been ridden due to lockdowns, moving house, a new baby, etc. The bike has never been in an accident (not even dropped off the stand!). I regularly run the engine, and only recently the fuel level has dropped enough for the light to come on. I haven't removed the tank or fiddled with anything regarding the fuel system, so figured I'd see what people suggest.

I was thinking of replacing a few misc hoses (purely precautionary reasons), so when I'm ready to do that I'll also pull the sensor unit out and have a look at it in more detail. :)
 

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The Bird I just got (and put together) does this as well. My light turns on somewhere around a quarter tank so it's not so bad.. but I had a ninja 650 where it was the only fuel indicator.. I ended up making one and it worked perfectly. But for the Bird I thought maybe it was coming on early because these things are so darn hot..with all that heat, the fuel in the tank can heat up especially as the fuel gets lower in tank. I may just leave mine alone because it's not a terrible thing for it to turn on at a quarter tank
 
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