My WR250X's low fuel light came on at 50 mi today. It never comes on at less than 90 mi. It went off and came back and I turned off the ignition, checked the fuel level (about half full), and rode a little more and it came back on under braking. So something's loose or broken to cause it to illuminate with a half-full tank.

I let a photographer and his assistant borrow it at the local roadrace track this past weekend and they rode it for 19 mi, including bumpy off-road terrain.

I have no idea how the low fuel sensor works. Would I have to take off the fuel pump from under the tank to fix it?

What year WR250?

In a 2008 the light should come on with .5 gallons left (2.1 liters) of fuel remaining in the tank but most come on around 80 to 90 mles on the road. I am confused on how it works too since I have never heard of a low fuel sensor assembly or anything. I would guess that its part of the fuel pump in the tank. Maybe a float of somekind. Guessing here.

Sounds like the sensor is bad or needs to be slapped around. You can take it apart, try finding the part on one of the yamaha parts sites with the micro fiche type blow up diagrams. From the manual, it looks like its only part of the fuel pump assembly. I had a similar problem, but started working fine. Probably just getting hung up. Here is a thread with more info. Good luck! http://www.thumperta...ad.php?t=719161

Not sure exactly how the low fuel sensor works, but I can tell you it is not available as a seperate part. It is part of the fuel pump assembly and you will have to replace the entire fuel pump assembly to fix it if it's bad. Unless the bike is still under warranty, I wouldn't worry about it right now. Just keep track of your mileage closely. The fuel pump assembly is NOT cheap.

mine does this as well usually comes on around 75-80 miles depending on how the bike is sitting and then when i start moving it goes off then comes back on in like 10-20 miles

Dammit, after filling up it came on again at 53 mi. It's broken and I don't know how to fix itl.

If it's that upsetting buy a new fuel pump. Spendy but will fix it.

might just be dirty. i know with gmc/chev p/u from 1999+ they had an additive to clean the fuel gauge pick-ups in the tank. probably a lot cheaper than a new fuel pump.