G'day Members.

Recent few days riding saw me have an unfortunate out of fuel event 12km short of next town. Good riding companions helped out with some fuel but I have few questions.

I travelled 288km from full tank. What distance can I expect from full tank?
Is the fuel pump capable to get all fuel in tank or is some left?
Once I filled up I put 17 litres in to fill it. I thought capacity was 19 litres. Is that correct?

Additional background. When I re-commissioned it in 2020, I replaced fuel pump, mounts, filter, hoses and gauze filter.
I did not replace hose that fits on to the gauze filter.
Does this hose scavenge the last of the fuel? Because it appears that the pump intake does not go all the way to the bottom of the tank. 
If so, how do you get replacement hose to lay in the bottom of the tank because attachment point on gauze filter is pointing up? Is it molded shape? Also how does it draw fuel when it is mounted higher than the bottom of the pump which by now is sucking air?

Also my low fuel warning is not working, either globe or sensor itself. This is another issue I will work on.

Thank you all in advance for helping (I hope)

Kim. Oz.

Kim Hunter wrote:I did not replace hose that fits on to the gauze filter.
Does this hose scavenge the last of the fuel? Because it appears that the pump intake does not go all the way to the bottom of the tank. 

The hose doesn't scavenge fuel; it diverts air bubbles from entering the fuel pump and damaging it. Mine's been removed for 60,000 miles and I've had no problems. The theory is sound but I haven't read examples of such damage yet. Where is the return line dumping in your tank?

How far is your pump's intake from the floor of the tank? I usually get 224 miles from a tankful before the fuel starvation starts kicking in—around 50 miles per gallon during mixed elevation riding at 70mph or less with light headwind. The 1988 BMW service manual indicates a tank capacity for the K75 of 21L.

I got 320km at the most from my K100 and they hold 3 more litres than the K75 (except RT) Make sure the pump is as far down into the rubber mount as possible as that can cause the pump to starve early.

The pump is about 40mm / 1.5 inches from the bottom. 
the gauze filter seems to clip onto the rubber housing preventing it from going further down.
I have a look to see if I can get it closer to the bottom.

Kim Hunter wrote:The pump is about 40mm / 1.5 inches from the bottom. 
the gauze filter seems to clip onto the rubber housing preventing it from going further down.

The OEM 52mm diameter pump's filter cup is press-fit onto the pump; the OEM pump has locating bands pressed into its housing to position it into its vibration damper. The hose is not designed to do anything other than divert any air bubbles at the pump's intake out the fuel tank vent. Positioning it as Rick G suggests could be the way to go, especially if the pump is an aftermarket model without locating bands. Optimal mileage also depends on a clean air filter, good spark plugs, correct valve clearances, moderate speed, and clean fuel. A strong tailwind is also helpful. 

Where is the return fuel line dumping fuel into the tank—toward the front, toward the right side rear, or on the left side somewhere?

I made a journey through France kast Thursday. Pulled in to a services on the autoroute. Put in 20.26 litres. I did 20.40 and 20.23 litres some months back. In March replaced everything in the tank, pump, mount, damper, pipes, filter, basket. Cost me about 100 euros in total for the parts, no used parts.

The low fuel light should have turned on way before running out of fuel.

When low, the level sensor sends earth to the warning light, through the white wire, causing it to glow. Unplug the fuel tank connector and use a jumper wire between the white and brown wire, if the light glows, the level sensor in the tank might be faulty. If it doesn't glow, the fault might be in the instrument Cluster.

Edit: or the tank plug might be loose, rusty, frayed maybe.

Range depends on speed and load. 

My K75RT averages 270km touring with gear on the interstate at 145km/hr, and 320km daily riding at 80-120km/hr before getting the low fuel light.

++

I'm getting about the same range on my K75 as is Point-Seven Five above.

* Edit to the range listed in my post above. 

I have removed the flapper from the filler on my tank, so the tank holds at least a liter more than stock with the flapper.  That should add an additional 6-7% to the range before the low fuel light comes on for a bike with the flapper.

If you still have the flapper in your filler, my range numbers for reference to your situation are closer to 250 and 300km

I did some checking, and found the pump seated too in the rubber mount. Next time is workshop I will correct it and also do some testing on the fuel level sensor.
I think it could be faulty because when I got this bike it had been left standing for many years. The fuel in the tank smelt stale and like varnish.

Problems solved.
Found that the fuel pump not low enough in the mounting.
I have moved the pump as low as I can get it.
Also I have proved the fuel level sensor is faulty. Have order a replacement.

Thank you all for your assistance.