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Thread: crap gas mileage 1992 r100r

  1. #1
    Registered User
    Join Date
    Mar 2019
    San Francisco

    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

  2. #2
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    San Antonio, TX
    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
    Registered User
    Join Date
    Apr 2013
    Southern California USA
    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
    Registered User
    Join Date
    Mar 2019
    San Francisco

    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
    Join Date
    Mar 2011

    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.
    We are all here for a spell, get all the good laughs you can.
    Will Rogers

  6. #6
    Registered User Anyname's Avatar
    Join Date
    Jun 2007
    Portsmouth, NH
    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 likely to go on reserve at about 120 miles.
    BMW R bike rider, horizontally opposed to everything...

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