R100/7 Reserve?

Discussion in 'Old's Cool' started by Claim Jumper, Sep 23, 2010.

  1. Claim Jumper

    Claim Jumper will work for knobbies

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    Hey Guys, quick question. So last night i am on the freeway and I decide to open up the old girl (I have been doing a lot of work on it lately and have not had a chance to do WFO yet). Anyway things are going great and around 95 indicated it starts cutting out like it is running out of gas so I slow down, go to reserve and pull over and put in 4.5 gallons or so. Does this sound right for a stock R100/7 gas tank?

    Thanks
    #1
  2. Big John Sny

    Big John Sny Been here awhile

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    That is about where mine kicks in.
    #2
  3. Claim Jumper

    Claim Jumper will work for knobbies

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    Great. I haven't run many tanks through this bike and I have hard time believing that it really is ready for the open road. It does run down the road well. Is there any special procedure for the two petcocks for reserve?
    #3
  4. Big John Sny

    Big John Sny Been here awhile

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    just think of it as having two reserves. The one on the right is supposed to be a bit spaller for some years but it seemed to be pretty close to the same size on my 77 when I relined the tank. It is easier for me to reach the left hand reserve while I am riding, so if I am already on reserve I run on the right reseve untill it starts to sputter and kick on the left, or get to a gas station, whichever happens first. I am sure there are different methods for everyone. I heard that you can run one side in the on position and when it kicks go to the other side at on, then use the reserves one at a time to have more like 3 reserves, but that just seems like too much effort for me.
    #4
  5. Claim Jumper

    Claim Jumper will work for knobbies

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    Great, thanks for the info. The funny thing about these bikes is that everybody says how simple they are, but every procedure you do on them is complicated and cunfusing (at least to me). I think that is why guys stick with them and become such big fans, once they figure out some of this crap they figure they might as well get another one...at least that is what I plan on doing!
    #5
  6. bmwhacker

    bmwhacker Still on 3 wheels

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    My experience: As soon as you think you "know it all" something else shows up that will stump you...at least for a while. Old BMW ownership can be a humbling experience.:lol3
    #6
  7. Claim Jumper

    Claim Jumper will work for knobbies

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    Heck yeah, humbling but gratifying! I have loved my newer bikes they don't require much wrenching and to me that is much of the fun of motorcycles. With the R100/7 I know there is always stuff I can fiddle with/learn/improve.
    #7
  8. BKMLWR

    BKMLWR Wondering around...

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    just be sure to use both sides once in awhile, they will get stickey and then not usable when that 1st reserve runs out....then you have to stop and lay the bike on its side for a second....
    #8
  9. Rapid_Roy

    Rapid_Roy finally understands

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    It's not too much effort. I have to do it often when I ride with my friend with extended range tanks. I just reach down and flip the left side up. If I don't reach a gas station, I start to panic when I go on double secret reserve.

    In fact, I did run out because he was pushing it in SD.:lol3
    #9
  10. Rapid_Roy

    Rapid_Roy finally understands

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    Oops, this too.
    BTW, I have about 40k on my /7, and I have loved every minute of it (except when I hit that deer).
    #10
  11. fishkens

    fishkens Long timer

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    Bad deer.
    #11
  12. Bigger Al

    Bigger Al Still a stupid tire guy

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    :nod It's worth it, though.:freaky
    #12
  13. boxerboy81

    boxerboy81 Stay Horizontal

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    If this is a new bike to you, one of the things I'd suggest is to remove the tank, drain it, remove the fuel taps and inspect them.

    Don't be surprised to see lots of red flaky stuff if you haven't already done this. That's the tank liner and one of those "they all do that sir" things.

    I'd flush and clean the taps and the tank, and compare the lengths of the tubes. If they've been trimmed then you'll have a shorter reserve.

    It's a 24 litre "S" tank right?
    Fuel Tank Capacity: 24 litres / 6.34 gal US. 3.78 litres per usa Gall.
    This is how I work it....
    If the tap tubes are as they were when new (and not cut shorter) then you should run for 21 litres (5.5usGall) before res #1. I do right tap to res. then. Another 1.5litres of use to 22.5 litres (5.95usGall) to res #2. I do left tap to res. then...and look for a top up soon.
    In reality it's a tad under 24 litres to empty. I think it's very difficult to actually squeeze the full amount in there.

    On average I get about 15kpl, but that depends on how I'm riding at the time. Mountain riding with the rpm seldom below 5K the usage can go down to 10.5kpl. (about 40mpg)

    So I figure that when I get to 1st res I have 45 ks absolute max distance to go, more if I'm careful with the throttle.

    Over time with more use, your cerebral fuel gauge will know what your tank is doing re: fuel left and when to fill. You'll make your own calcs often enough.
    #13
  14. Claim Jumper

    Claim Jumper will work for knobbies

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    Thanks for the info boxerboy. I had the tank off in the spring when i lined it with POR 15 and I rebuilt the petcocks then. At that time only one of the petcocks had an in tank fuel filter so I replaced them both.
    #14
  15. Sniper X

    Sniper X De Oppresso Liber

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    HAHA! :roflI JUST posted a thread on this exact same question about a week ago! My 1978 R100RS goes on reserve right at 145miles....and there is at least 2 gallons left in the tank at that point. BTW when I fill up when it goes on reserve, almost exactly 4.5 gals go in!
    #15
  16. bmwhacker

    bmwhacker Still on 3 wheels

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    +1000:thumb
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  17. Jasper ST4

    Jasper ST4 Guest

    I replaced my petcocks recently with the 90 degree ones and they also hit reserve at 4.8 gallons.
    #17
  18. boxerboy81

    boxerboy81 Stay Horizontal

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    You guys are getting different numbers to me.

    My 11/1981 R100RS with Germa taps hit reserve today at 335ks or about 211 miles. This was 80% 100-120kph at reasonably steady hwy throttle, the rest commuting. I'm very happy with that fuel consumption.

    I rode about 18ks home after switching to the right reserve,

    I drained the unused left reserve of 1.9 litres. If the right side is identical, then reserve on this tank is at 20.2litres (/3.78 = 5.4USgall)

    My previous BM's all had Karcoma taps and I remember doing a calc years ago that the reserve was 1.5 litres per side, but my current bike has Germa taps. Might there be a difference in the reserve tube lengths? I guess any previous owner may have fiddled with the lengths?

    I have just bought some angled Karcoma's to put on this tank. When I get them in a few weeks, I'll do a similar exercise and compare the pipe lengths and the reserve numbers.

    Are my conversions to US gallons right?
    #18
  19. bpeckm

    bpeckm Grin!

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    Reserve depends not on the brand of tap, but on the shape of the tank and how long each straw is.... the longer the main straw, the sooner you will run it out of that fuel, and go to your reserve.

    Imagine two straws sticking up from the bottom of a glass: it will draw gas out of the tall (main) until that straw is level with the water. Then you can draw out of the short straw (reserve) until you get to the top of that one... that is when you are empty.... BUT if you can shake the bike around and get all of the residual gas over to ONE side, you will a little bit left... use that, and you are indeed e.m.p.t.y. .....:D
    #19