K75 fuel capacity problem

[weichesatan]

I just joined to tap into some of your knowledge.  A brief introduction.  I own and ride a 1988 K75C with 169,000 original miles and recently acquired a 1995 K75 with 30k miles.  The newer bike is the one I have some questions about and will just deal here with the most-troubling issue and see what you all think.  BTW, the K75 is the only motorcycle I will ride, as I consider it closest to perfection.

The 1995 low fuel warning light comes on at 165-170 miles.  At first I thought this was simply a malfunctioning warning as it should come on, like my other bike, around 200, depending on riding style.  They tanks should both have a bit over 5 gallons, not the 4 indicated.  So, I continued riding and the bike sputtered at 208 miles, suggesting that it was running dry after 4 gallons. 

I checked my Clymer’s manual and looked into the fuel tank and the pump is seated properly and the float is free and seems to move as it should.  My question, of course, is what might be wrong as the tank is running prematurely dry?  I am getting 47+ mpg.  This is cutting down my range and I am needlessly carrying an extra gallon.  Out here in Wyoming, that inaccessible gallon could mean the difference between getting home to my warm bed and spending a cold night outdoors with the pronghorn antelope.  Any ideas appreciated.

[kennybobby]

Maybe you need to  bend the arm down a bit to indicate the 4L warning closer to the actual 1-gallon-to-go point.  Take the fuel cap off so you can get your hand in there to adjust the arm.  drain the tank and refill with 1 gallon or so, then adjust the arm by bending until it just comes on.  It will be close enough, i don't do metriscles.

[Chaos]

when it sputtered and died was there a gallon of gas still in the tank?  That would indicate a pick up problem.  5 gallons is optimistic,  even with the flapper removed.  Most mine has ever taken is about 4.7. 

[weichesatan]

when it sputtered and died was there a gallon of gas still in the tank?  That would indicate a pick up problem.  5 gallons is optimistic,  even with the flapper removed.  Most mine has ever taken is about 4.7.

Yes, there had to be a gallon in it because only 4 gallons topped it off at the gas station.  I believe the manual states that the fuel capacity is 5 gallons.  The beauty of it is I have another k75 so can compare, and the discrepancy is significant.

[brianhinton]

My 1987 K75T fuel warning light comes on religiously at 175 miles...like clockwork. The 1995 K75S that we just sold came on at 172....and sometimes in the 180's depending on riding style.


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[weichesatan]

Maybe you need to  bend the arm down a bit to indicate the 4L warning closer to the actual 1-gallon-to-go point.  drain the tank and refill with 1 gallon or so, then adjust the arm by bending until it just comes on. 

So you're saying, with a gallon in it, bend the float rod down until the fuel warning light comes on?  Wonder how this would get so out of spec?

[weichesatan]

My 1987 K75T fuel warning light comes on religiously at 175 miles...like clockwork. The 1995 K75S that we just sold came on at 172....and sometimes in the 180's depending on riding style.

Interesting, but inexplicable.  That would mean you're getting 43 mpg.  Out here on the open roads I'm getting 47-50 and so around 200 is what I should be getting before the warning lamp goes on.  Humm....

[weichesatan]

the bike in question sans battery covers, since replaced...

[kennybobby]

a previous owner may have bent the rod while changing the fuel filter or pump, etc.  there is no way to know the past, but you can set the rod to indicate whatever level you desire now that it is yours.  Put a gallon in and bend until the light comes on, then lift the rod slightly and the light should go off.  Tweak the rod position so the ball is floating and just comes on at the level you desire.

i get about 56 mpg on the high end, so around 200 the light comes on and i start looking for pure gas, i don't buy ethanol except for gallon jugs or brown bottles for party liquer...

[weichesatan]

Thank you all. I will try that and report back. No ethanol premium is what I burn.

[Chaos]

bending the float rod  not going to address the problem of the fuel pump not sucking all the gas out of the tank.  Might want to replace the rubber hoses in the tank

[The Mighty Gryphon]

The only thing that controls how much fuel is left in the tank when the engine stops running ffrom fuel starvation is the mounting of the pump.

Sputtering is not stopping.  Carry a gallon of fuel in a can and run the bike until it STOPS.   That is the only way to really see how far you can travel.

[weichesatan]

Well, sounds like there are two schools of thought here.  Can anyone answer this: Does the float mechanism shut OFF the fuel flow through the pump?  If it does, then bending the float wire would make sense, if not, then I would concur that the float would not affect the flow of gas if there is a gallon in it. 

Thanks.  I'm not a mechanic but a teacher.  After being burned by TWO incompetent regional BMW dealership service departments, I am doing all I can to work on my own bike and your input and time is appreciated.

[Laitch]

Does the float mechanism shut OFF the fuel flow through the pump?   

No. It's purpose is to indicate the remaining fuel supply.

[kennybobby]

Sorry if i mislead you--i was focused on your issue of the 4L light coming on with more fuel in the tank, and what you could do to 'calibrate' the rod to indicate the correct amount remaining. 

As stated the rod has nothing to do with the pick up by the pump.  Make sure the pump is pressed into the holder as deep as possible and the clips are pressed in until they latch.

The Haynes manual says capacity is 5.55 US Gallons, but not sure you could ever put that much in or use it all--seems like i pumped a tank empty to drain it and there was still at least a quart left that the pump couldn't pull out.

[Laitch]

My 1987 K75T fuel warning light comes on religiously at 175 miles...like clockwork. The 1995 K75S that we just sold came on at 172....and sometimes in the 180's depending on riding style.

Interesting, but inexplicable.  That would mean you're getting 43 mpg.  Out here on the open roads I'm getting 47-50 and so around 200 is what I should be getting before the warning lamp goes on.  Humm....

Part of your bafflement, weichesatan, might be the belief that German engineering=pinpoint accuracy. Well, that's not exactly the way it works with this system. A fast ride into a headwind uses more fuel than a relaxed tour on secondary roads so the fuel level lights sooner because the mpg is lower. The tank isn't designed to be emptied completely so until it's remaining contents are emptied into a container and measured after the bike has stalled from fuel starvation, using assumptions about the amount of remaining fuel to calculate mileage are unlikely to be useful.

Gryph, in a previous post in this thread, has explained the way many of us have adapted to this light's function. To learn what's what, carry spare fuel, run until the light comes on then track how many more miles you get until the engine cuts out and won't restart without more fuel. Do that a few times in mixed driving and you'll soon know when to start panicking after the warning light is triggered.

Another factor affecting the light's accuracy is the condition of it's electrical components. Read this well-written, illustrated article for further understanding.

After I ran a few experimental rides, I learned that my fuel sensor light would be triggered between a reading of 140 miles and 180 miles on the odometer. At 140 miles I could still ride approximately 80 more miles then the engine would quit. The most fuel I've put in at a fill-up has been 4.2 gallons. Usually it's between 3.2 and 3.6. Based on what I've learned from my trials, I can work with that.

[rbm]

The fuel level sensor has an adjustment mechanism built into it to calibrate the level of fuel that turns on the low fuel warning light.  Bending the float arm is not necessary and not recommended.  The adjustment is a toothed wheel that can be rotated. 

• Rotating the wheel CLOCKWISE will cause the wiper to contact earlier, resulting in a LARGER reserve volume.
• Rotating the wheel COUNTERCLOCKWISE will cause the wiper to contact later, resulting in a SMALLER reserve volume.

[Chaos]

My light started coming on around 130 miles instead of 180 when the speedo got flakey and only worked part time.  Stealing gas out of the tank for the lawn mower probably didn't help either.

[Chaos]

Part of your bafflement, weichesatan, might be the belief that German engineering=pinpoint accuracy.

Caution, Laitch,  he did say "BTW, the K75 is the only motorcycle I will ride, as I consider it closest to perfection."  Let us not burst that bubble!