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Thread: Intro to the K75 Motorcycle - 101 - Fuel Capacity

  1. #1
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    Intro to the K75 Motorcycle - 101 - Fuel Capacity

    OK, I gotta admit that I did not expect this. My sister asked advise (I am rarely in short supply) on a starter motorcycle and steered her to a K75 for her first bike. She is 45 yo and new to motorcycling. The rational was that it is not hard to manage and would last her a lifetime.

    So I test rode it for a while, and received some great advise here on common maintenance issues to keep her riding. As great a bike as the K75 is, it doesn't compare in performance or much else to my to date favorite scoot, a 2008 K12S. But whatever positive attributes the K75 has, it has in sufficient quantity that I just purchased an Arctic Silver 1995 K75 with ABs myself, and am considering selling the K12S.

    But I need some help, too. So exploring this bikes attributes may take this thread down a wondering path. The first, very strong concern about the K75 that I would appreciate help with is fuel capacity.

    The riders manual states that the fuel capacity is 5.2 gallons. But after running the bike to fumes, the most that I can get in the tank is 4.55 gallons. I can easily travel 700+ miles per day on this thing, and with a custom seat, that could increase substantially. But stopping between 160 and 190 miles per full tank for fuel is discouraging.

    Is there a way to increase this bikes range? I have heard of fuel bladders that extend the range, but cannot find them for sale on the internet. What other options are available for increasing the fuel capacity of this bike? Any thoughts or recommendations appreciated.

  2. #2
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    You should stop about every two hours just to stay mentally alert. It may not seem like it matters, but it does.
    Top the tank, walk around 5-10 minutes, take a whiz, get some coffee/coke, etc.
    It makes for safer riding.
    '03 R1150R, '03 F650GS, '97DR200SE,'78 Honda CT-90, '77Honda CT-90

  3. #3
    We - Voni and I - have owned 7 K75s. Still own 3. All of them held a usable 5.2 or so gallons, and I adjusted (bent) the float arm so the light came on with one gallon usable left.

    If yours was on fumes at 4.5 or so then I suspect that the fuel pump is mounted too high in the tank. Unless modified the pump fits down into a recess in the tank and is held down in place by two clips on the white nylon (?) mounting ring. If not pressed completely down and clipped in place the pump leaves fuel sitting below the pickup in the bottom of the tank.
    Paul Glaves - "Big Bend", Texas U.S.A
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  4. #4
    Mars needs women! 35634's Avatar
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    Does the tank still have a flapper valve? Removing that can give you an extra half gallon with no harmful side effects.
    1987 K75S
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  5. #5
    Dum vivimus vivamus ted's Avatar
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    I generally get about 200 to 210 out of a tank and it usually takes between 4 to 4.2 for that, less if I am really riding hard. I've never had a problem with that, it is actually nice to get off and stretch for a bit. If I needed more I would probably get one of the 5-gallon fuel bladders for inflatable tenders from West Marine and strap it to the back seat.
    Ted
    "A good stick is a good reason"
    1994 K75RT
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  6. #6
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    Quote Originally Posted by Ted View Post
    I generally get about 200 to 210 out of a tank and it usually takes between 4 to 4.2 for that, less if I am really riding hard. I've never had a problem with that, it is actually nice to get off and stretch for a bit. If I needed more I would probably get one of the 5-gallon fuel bladders for inflatable tenders from West Marine and strap it to the back seat.
    Well, yea you're right. Crossing from California to Houston on I-10 isn't fun, and we hit a heck of a dust storm in El Paso Sunday. Whew, it was blowin' some dust. So I was averaging about 85 mph. The speed limit on I-10 in extreme west Texas is 80, so I wasn't too out of bounds legally, but for a K75 that might be pushing it. But impressively, the bike acted like all was fine at those speeds for the entire day.

  7. #7
    gentleman rider Astrin's Avatar
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    Well, in fifth gear, you're not too far above the 6250 RPM torque peak at those speeds, so the bike is quite happy. Yeah, it gets noticeably louder at those speeds, but it's definitely built to ride up there. And, of course, it just purrs at 62 MPH, which is my standard speed on 55 MPH roads (Wisconsin cops usually give you 7 MPH).

    BTW, when mine's been down to fumes, it's filled a full 5 gallons. But I can fill mine right up to the cap, I think many have the flapper that cuts out a quart or so. That gives me a 250-mile range, and the light comes on at about 1 gallon, or 50 miles, left. I use the trip odometer as a fuel gauge.
    Sam Hokin, Madison BMW Club | Facebook | Flickr
    1991 K75RT (130,000 mi) road | 1983 KZ440 fun | 2006 SV650 track
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  8. #8
    rcbimmer 67972's Avatar
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    When you guys bend the flap can I assume that you bend it upwards. My light comes on at around 120 to 150 miles.
    Robert Cantrell
    Spring Hill, Fl
    92 BMW K75S 73 BMW R60/5
    14 Suzuki Vstrom 1000

  9. #9
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    Quote Originally Posted by 67972 View Post
    When you guys bend the flap can I assume that you bend it upwards. My light comes on at around 120 to 150 miles.
    Flap= the spring loaded 1" diameter flap the the gas pump nozzle opens under the gas cap. Primary function=to prevent the use of an unleaded fuel. It also prevents the tank from being filled higher than about 2" from the top.

    Remove 4 screws from base of gas cap assembly, then invert assembly and remove 3 screws that hold flapper assembly to gas cap assembly.

    Store flapper in that safe place in your garage that you've got all that crap that you think you should save but can't quite remember what it's for.

    Reinstall gas cap assembly. You now can SEE what your doing when you fill the tank. You also can monitor the condition of your fuel pump vibration damper. AND you can put more fuel in the tank. I regularly fill to with in 1/2" from the top with no ill effects. More miles per tankful.


    As far as when the low fuel light comes on, that is controlled by the float arm on the right side of the tank (inside). If you bend the wire so the float ball is lower, the light will come on later.

    Ideal is when the light comes on with 1 gallon USEABLE fuel left. That way it's easy to calculate how many miles you have to find gas. Your MPG= maximum miles till stranded.

    Best policy is to look for gas as soon as the light goes on. That should give you at least 35+ miles, but those miles better not include any hard cornering or acceleration as the fuel at that level is prone to wash away from the pump and cause hesitation (not what you want when trying to cross a four lane highway in front of an oncoming semi).




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
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  10. #10
    Registered User beemerguru's Avatar
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    The other possibility was the change in tank capacity around '93 or so. I got a factory replacement tank when the paint peeled on a new K75 back then and immediately noticed a decrease in range.

    Popped the tank off and compared it to another off an earlier K75. There was a change in the bottom design..took away about 1/2 gal.

    Called BMW and got my old tank back..repainted it and got my 1/2 gal back.
    Greg Hutchinson
    R80G/S (4) 633CSi with 450K mile
    '68 R60/2 '88 K100RS Special Edition
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  11. #11
    Bob T
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    Quote Originally Posted by 98lee View Post
    Flap= the spring loaded 1" diameter flap the the gas pump nozzle opens under the gas cap. Primary function=to prevent the use of an unleaded fuel. It also prevents the tank from being filled higher than about 2" from the top.

    Remove 4 screws from base of gas cap assembly, then invert assembly and remove 3 screws that hold flapper assembly to gas cap assembly.

    Store flapper in that safe place in your garage that you've got all that crap that you think you should save but can't quite remember what it's for.

    Reinstall gas cap assembly. You now can SEE what your doing when you fill the tank. You also can monitor the condition of your fuel pump vibration damper. AND you can put more fuel in the tank. I regularly fill to with in 1/2" from the top with no ill effects. More miles per tankful.
    Outstanding...Thanks!
    I just did this to my '95K11....

    Not so worried about capacity, but I like to see the gas as I fill her up....

  12. #12
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    Fuel Pump Placement

    I am hoping that the fuel capacity is due to the improper replacement of the fuel pump, and indicated as a possibility by Paul. I noticed that the POs notes indicated some fuel pump work, but we've had company so there has been no time to check. The bike performs well, so it was replaced and working well, but may be riding too high in the tank to suck out the last bit of fuel.

    Would love to have the ~250 mile range that the R12R does... Will know more in a few days.

  13. #13
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    Quote Originally Posted by gregfuess View Post

    Would love to have the ~250 mile range that the R12R does...
    Not going to happen, unless you're willing to end up on the side of the road out of fuel and who knows how far from the nearest gas station just to reach some magic number.

    Should easily be able to get to at least 160 or more (depending on your riding style) before the 1 gallon to go, gotta look for gas light comes on.

    I always end up near the low end (160- 175) because I am NEVER trying to get good MILES per gallon on a straight flat road at the speed limit. I guess some one MIGHT be able to get close to 200 before the warning light comes on on a flat straight road with no wind and at a constant 55mph, but what fun is that (and that means that you've been in the saddle for almost 4 hours to do it)?

    As I said before, riding with less than 1 gallon in the tank can result in the bike stuttering under hard acceleration or cornering as the fuel temporarily washes away from the pump. Starving the pump can also cause damage to the pump if done often enough.

    I'm always looking for SMILES per gallon on twisty mountain roads and the big numbers on the signs are just just helpful advisories to make sure I'm in the right gear so I don't overcook the blind corners.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  14. #14
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    Quote Originally Posted by gregfuess View Post
    I am hoping that the fuel capacity is due to the improper replacement of the fuel pump, and indicated as a possibility by Paul.

    but may be riding too high in the tank to suck out the last bit of fuel.
    Quite possible. Even in the correct stock position, they ride too high to pickup all the fuel (might be on purpose so they don't pickup the sediment or water in the tank in areas with poor fuel??)

    I've moved mine down, past stock, 3/8-1/2" so the strainer JUST touches the tank. Worth doing to maximize range if you aren't consistently in an area with questionable fuel and you don't let the bike sit for months at a time.



    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  15. #15
    Registered User breyfogle's Avatar
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    Quote Originally Posted by gregfuess View Post
    I am hoping that the fuel capacity is due to the improper replacement of the fuel pump, <...snip...> Would love to have the ~250 mile range that the R12R does... Will know more in a few days.
    K75's will do 175 to 190+ before the low fuel indicator lights up (with the flapper removed). After that, its up to you about how much reserve fuel to burn. I figure I could go, maybe, 225 miles but I'm not comfortable doing so.
    '89 K75S Original Owner
    '94 (Beta) R11RS, ( RIP 12-5-2010 courtesy of blind left turning cage driver ) ....

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