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Thread: 93 R100pd Fuel Mileage

  1. #1
    Registered User
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    93 R100pd Fuel Mileage

    THIS 93 PD IS MY FIRST BMW AND IT IS VERY LIKEABLE. I AM GETTING TERRIBLE FUEL MILEAGE (32-34 MPG) AND I AM WONDERING WHERE TO BEGIN. I DID NOTICE SOME FUEL "SEEPAGE" FROM AROUND THE CARBS BUT HAVING RUN F.I .BIKES IN THE PAST-I FINALLY GOT USED TO CLOSING THE FUEL SHUTOFFS ON BOTH CARBS AND THE SEEPAGE HAS STOPPED.

    OTHER THAN REPLACING THE PLUGS AND CHANGING THE MOBIL ONE I HAVE DONE LITTLE ELSE TO THIS 50K BIKE. WHERE SHOULD I START WITH SOLVING THE PROBLEM?

    THANKS KEVIN A.

  2. #2
    Registered User lkchris's Avatar
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    Diaphragms.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S, '84 R80G/S

  3. #3
    Rbike
    Guest
    My 93 PD also gets 33 mpg no matter what. It recently got the same mpg riding two up in the mountains and communting back and forth to work.

    Just a little seeping out of the carbs coud be worth 1 or 2 mpg. Like Ken wrote, make sure the diaphragms aren't torn...and then be sure the carbs are properly balanced.

  4. #4
    HMFIC
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    PD Fuel Mileage

    my last tankful got me 303 miles and it took 8.3 US gallons to fill it. Somewhere around 36.5 mpg
    I was kind of happy with that, considering 250 miles of that was at 75 to 85 mph and the rest commuting with plenty of stop signs and traffic lights.
    1992 R100PD
    Bob

  5. #5
    Registered User
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    SO IN OTHER WORDS, IF I AM IN THE THROTTLE AND RIDING IN THE OZARKS-I AM PROBABLY NOT GOING TO GET A WHOLE LOT BETTER THAN THAT? MAYBE HAVING THE CARBS RE-BUILT ETC IS A GREAT IDEA BUT MAY NOT BE NECESSARY-
    THANKS FOR THE INPUT-KA

  6. #6
    Registered User lkchris's Avatar
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    "Carbs rebuilt" is a way more daunting sounding term than is really applicable with Bing carbs.

    All you really do is pull off the float bowl cover and replace rubber o-rings on the main jet carrier and on the idle mixture jet. The idle air jet has one, too, and is accessable outside the float bowl area.

    A "kit" will probably also include a new gasket for the enrichener (choke) cover and an o-ring for the shaft of the aux carburetor that's under there.

    Most of the time that's all you need to do, but every other time or even less often it's good to replace the float needle and also the slde needle and needle jet, as all are subject to some wear.

    After 20 years I finally replaced throttle shaft o-rings on my bike and didn't think it was really necessary after the fact.

    The biggest recurring problem is tears in diaphragms, which require removal of the top cover.

    You may spend more time resynchronizing the carbs than you do replacing the rubber and perhaps some of the moveable jets.

    Pictures of all these parts are available in exploded view here .
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S, '84 R80G/S

  7. #7
    HMFIC
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    I knew it (36.5mpg) was tooo good to be true, yesterday the mileage dropped to 28.5 mpg. This was riding 2 laners for about 200 miles.
    Bob

  8. #8
    Rbike
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    My mpg can drop down like yours when I run above 80mph. At 90mph it falls to about 25 mpg

  9. #9
    Narcaleptic Insomniac TZOLK's Avatar
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    PD MPG

    On a trip to New York last week with jesse bags filled, a tent and two folding chairs riding highway and two lane RT#6 in PA my 1990PD was getting 40 mpg. Everytime we filled up, after the calculations, it was always 40mpg. My girl was getting 74mpg on her F650GS worst for her was 64mpg. So guys, whats the real capacity for the PD tank? I dont think it is 9.2 like the book says. Maybe more like 8.2??? It probably doesnt matter but do any of you ride with one or the two petcocks open. Also, at the auto parts store they have vinyl(colored plastic) vacuum port covers and some are big enough to fit snugly over the pilot mixture screw housing to just "make sure" no more air leaks up through the o-ring. Havent done diaphragms yet.

  10. #10
    Rbike
    Guest
    Having pushed my PD about 100 yards into a gas station, I've found that it holds 8.4 gallons.

    And yes, I ride with just the left petcock open without any problems. I have tried another time to see how much fuel is left on reserve, and if I open the second petcock after the first runs dry on reserve, there is only enough fuel for a couple of more miles. I don't remeber exactly how many but it still filled with only 8.4 gallons.

    Since I am living at a bit over 5000 ft. where engines will make about 20% less power than at sea level...I guess my 32 mpg is about equal to your 40

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