In restoration of my '90 K75 I mucked about with the gas tank and took the sensor mechanism out. Since putting it back together I've been wondering if the low fuel light works -hadn't seen it - and what it signifies in amount of fuel left. So this afternoon filled with curiosity and no sense, I drained all the fuel I could with a siphon. The light does work. But then tried refilling it 16 fluid oz/1pint at a time to see what it took to turn off the light. Answer was:
reserve comes on between 80 fl | .5 gal |  2.5qt | 2.3 liters
and                                  96  fl oz| .75 gal | 3qt | 2.8 liters
This isn't quite the same as my '91 K75 which gets about 50 miles after the fuel light comes on. So I'm thinking of doing another check by simply running the bike out of fuel and noting when the light comes on and how much further it can travel before being out of fuel.

Does anyone know of a more sophisticated or useful method?
best regards
J. Jefferies

NO,i did what you are thinking of, i carried 3 ltr canister in a pannier then ran until  light on then ran it dry.Put the 3 ltr in rode to garage and filled up 

The easiest check I know of is to run until the Light comes on.  Note the mileage on the tripmeter and fill the tank as soon as possible, noting the mileage and amount of fuel when you refill.  Do it 5-6 times to get a good idea of when the fuel is running low. 

The K75 tank holds about 5.3 US gallons, my experience is that in normal riding around town the K75 gets about 45 to 48 mpg, and the low fuel light comes on at about 190 miles.  Touring at 85mph on the interstate into headwinds lowers the fuel efficiency to as low as 38mpg.

I have removed the flapper in the filler on my bikes.  I fill to the bottom of the filler neck, and after the low fuel light comes on the tank will take about 4.5 US gallons.  This means that there is .8-.9 US gallons remaining which is reliably capable of running another 25 miles before the pump begins to cavitate.

I mentally calculate fuel mpg every time I fill up the tank.  If you don't do it, it's a good habit to get into.

on my 1988 K 100 RS the light comes on at around 100 miles when traveling at steady speed around 120 . I fill it and it takes around 2.5 us gallons ,sometimes less. sometimes more depending. I like to keep the fuel pump covered in fuel to keep it cool so I'm good with filling every 100 miles anyway. When I do my gas mileage checks I usually am getting between 45 and 50 MPG

Checked mine yesterday. Whew! what an adventure when you don't check your route ahead of time. Almost screwed the pooch. Poor pooch. Picked up a gallon in a small carry tank. Took off to BMW of San Jose down 880. Hey what could go wrong? Right? 880 a road I know well and hate. Low fuel light came on half way down the 40 mile trip. Got down to the shop and picked up a set of hinges for the integral bags and put them on right there in the bright sunshine. And decided to come directly back. Ten miles further on bike starts the "I'm out of fuel" stutter. I'm thinking I'll just pull off the road and put the extra gallon in once it's completely out. Then I notice that there's new road construction going on. The right hand side (the off side for you Brits & Aussies) is completely closed off with concrete barriers. Ouch! And it looks like it goes for several miles like that. Doubts as to whether I can make the next exit ramp before total fuel exhaustion. Zip over to the center where there's still a bit of off road/break down space and stop. Most vehicles passing me are doing 80 mph. Biggest concern was a vigilant CHP might come by and try to help - which wasn't needed. Put in the gallon and put everything back into place and waited for a break in the traffic flow and took off like the proverbial bat out of hell. Not a major issue just a bit of a screw up on my part relying on recent memory of that road.
Bottom line, 30 miles of freeway travel on an essentially flat surface at 80 mph. My other K75 will get about 50 miles and it has a barn door fairing on it. Wonder if you need to recheck these numbers anytime you remove or mess with the float/reserve fuel assembly.

I read somewhere that you add a piece of hose to the internal return pipe from the FPR. You then feed it over so it returns next to the pump, this will slightly increase mileage in a emergency situation. It will also keep the pump a bit cooler in a low fuel situation.
Regards Martin.

MartinW wrote:I read somewhere that you add a piece of hose to the internal return pipe from the FPR. You then feed it over so it returns next to the pump, this will slightly increase mileage in a emergency situation. It will also keep the pump a bit cooler in a low fuel situation.
Regards Martin.

Thanks, but think I'll just try to keep it fueled properly. Only time I've ever seriously run out of fuel was leaving Death Valley two up. Thought I had at least 40 miles of spare but a head wind and up hill ride cut it in half. A passing dirt biker was able to spare a half gallon which got me to the next gas station. Bless him.
And since then I pay attention to the light and to my trip odometer which I reset at each fueling.

Speaking of trip odometers - not to hijack the thread - but I recently fixed mine on this silver project bike. It had lost the circlip that keeps the reset knob in. Anyway I've now noticed that when I reset the trip  odo it takes more than one rotation to get back to 0 and then it'll show  1.0. Always the first digit is off. On my regular ride I have an Avocet bicycle speedometer which provides a secondary trip odo. But it's a pain to install the sensor ring. So, has anyone had any experience with the new GPS driven speedo/trip odometers? Know it sounds weird but I've been a bit hesitant thinking that a speedo using GPS just sounds imprecise or something.

MartinW wrote:I read somewhere that you add a piece of hose to the internal return pipe from the FPR. You then feed it over so it returns next to the pump. . ..  It will also keep the pump a bit cooler in a low fuel situation.
Regards Martin.

jjeffries wrote:Thanks, but think I'll just try to keep it fueled properly.

The modification Martin mentions is described in this service bulletin. The point of it is to help fuel the pump properly. The need for it is based on riding style. Somebody who is able to fill the tank every hundred miles won't need it. Somebody cutting a razor thin margin between fuel stops and fuel starvation in and out of the twisties might consider implementing it.