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Thread: crap gas mileage 1992 r100r

  1. #1
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    crap gas mileage 1992 r100r

    just ran through my first tank of gas. i went to reserve at not much more than 100 miles. demoralized
    my /5 always gets over 40. it has the smaller carbs "32mm." and seems to running swell,this was mostly city riding, lots of hills and fairly aggressive but not stupid.
    the valves are adjusted and the carbs are tuned and balanced. however not rebuilt.
    any ideas why the mileage might be so poor
    thanks

  2. #2
    Liaison 20774's Avatar
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    Other than such bad gas mileage, does the bike perform well as in acceleration, start and idle well, etc.? Can you go any speed you want like do you think the bike would get up to say 80-90 mph? I suspect with the poor mileage, your plugs are nearly black with soot.

    Things that come to mind:

    - plugged air filter
    - holed diaphragms in the carb
    - choke is always on
    - sinking floats

    Let us know what you find.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
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    Verify that the speedo is counting miles correctly with a gps or mile markers, then fill up the tank and run it through and check next fill. Do the math, miles driven, gas used. My r100r never did as well my /6. The r100r was lucky to do 42 mph, usually only in the high 30's. Good luck. Chunk.

  4. #4
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    carb rebuild

    i have all the parts in hand to rebuild the carbs,diaphragms and floats included
    i will have a look at the plugs
    the bike seems to run quite well at all speeds,up to 75 or 80 anyway
    i will check the choke and make sure it is completely off in the off position
    i was putting off the carb rebuild cause i was really enjoying the ride
    thanks for the advice

  5. #5
    Registered User tanker4me's Avatar
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    Mileage will vary.

    The cause for your issue may be with one of the things mentioned above, or not.
    The stock /5, /6 & R100GS Airhead bikes I ride have variations in range even when in good tune.
    When on my own, 40 MPG.
    Riding with the AMCA, 45MPG.
    Riding with the Airheads or SoCal Norton Club, 35 MPG.
    As little as 32 MPG, and up to 48 MPG.
    Bill
    We are all here for a spell, get all the good laughs you can.
    Will Rogers

  6. #6
    Registered User Anyname's Avatar
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    The only way my R80 will get 40 MPG is if there is a long hill I can coast down. The plugs look fine, and the heads were rebuilt last year, but it just gets lousy mileage. It's likely to go on reserve at about 120 miles.
    Last edited by Anyname; 06-05-2019 at 10:49 PM.
    BMW R bike rider, horizontally opposed to everything...

  7. #7
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    all seems well

    i have just completed a 200 mile trip on pretty flat roads and i got 40 mpg which seems to be normal.
    i did change the rubber sleeves to the air box
    i read that they may contribute to poorer mileage
    thanks for the help

  8. #8
    Registered User beemerguru's Avatar
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    R80G/S, dual plugged, PD tank..if I keep it around 60-65, I'll get 45mpg. Over 70, it drops to around 35.

    Rebuild the carbs, replace theO rings, needles and jets, check for air leaks, valves correct, carbs balanced? Timing right?

    Wander down to Redwood City sometime..have a few /5,/6,/7 builds going on.
    Greg Hutchinson
    R80G/S (4) 633CSi with 450K mile
    '68 R60/2 '88 K100RS Special Edition
    http://gregsgssite.shutterfly.com/

  9. #9
    There was a time 25 yrs or so ago when I got 33 mpg from my '84 R100, '90 Hawk GT and '96 Ducati 900SS. That always seemed just wrong. Might have been a wrist problem.
    '61 Clubman's Gold Star, '13 690 Duke, '13 Daytona 675R, '17 1290 GT, '18 Street Triple RS (gone but not forgotten: '76 R75/6, '84 R100, '76 R90S)

  10. #10
    Quote Originally Posted by tinkerer View Post
    just ran through my first tank of gas. i went to reserve at not much more than 100 miles. demoralized
    my /5 always gets over 40. it has the smaller carbs "32mm." and seems to running swell,this was mostly city riding, lots of hills and fairly aggressive but not stupid.
    the valves are adjusted and the carbs are tuned and balanced. however not rebuilt.
    any ideas why the mileage might be so poor
    thanks
    My first airhead, a 10 year old 1980 R 100T, gave mediocre gas mileage, mid 30s mpg. I found out that the compression was low and installed new rings and freshened up the valves and seats. Even before the parts were broken in mileage went up to mid 40s mpg riding conservatively.

  11. #11
    Just got back from a 3 day trip on my R90S. Average gas mileage was between 35 and 40 MPG. Two days of the ride was at Highway speeds - 55 to 70 MPH.
    My buddy was on a 650GS and was getting around 65 MPG. But then it's a new bike with Fuel Injection.

  12. #12
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    hey greg
    i may just wander down there and check out your shop
    i could use a little face to face chat

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