Airhead GS - Gas Mileage?

Discussion in 'Airheads' started by summerinmaine, Sep 27, 2004.

  1. Tim McKittrick

    Tim McKittrick Long timer

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    My R100GS was doing well to return 40 mpg- there are ways to improve things, though. With a set of 38 mm flatslides mounted, mt buddy's R100GS's mileage jumped almost 5mpg and made more power. If you add high compression pistons, dual plug the heads, and install a freer flowing exhaust, things will only improve. My Dad's R75/7 had dual plug heads, electronic ignition, 900cc Venola pistons(10.5:1) and an RS fairing and it regularly sipped it's fuel to the tune of 60 mpg at a steady 70 mph. Grab those wrenches and get busy!
    #21
  2. JamesJWeg

    JamesJWeg "Speedy"

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    I have found that on the 32 Bings the richning (choke) plate screws will get a little loose and cause your MPG rate to drop way off. It will also cause the bike to start hard or if it's minor to start better with little or no choke. Locktight is in order on those 4 screws. On my RT with 32 Bings I was getting only about 17 - 19 MPG and after fixing that one problem it jumped to around 32 - 35 MPG depending on wrist wieght.

    James.
    #22
  3. Mully

    Mully Kineticist

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    On all three of my airheads I found: 1) clogged atomizer ports, and 2) air leaks at the enrichener cover gaskets, 3) worn needle jets & needles. Fixing those problems improved mpg and roll-on smoothness.

    My two GS/PD's (`91 & `93) got on average about 38~40 and my `78 RS about 42~43. One guy I knew with a GS swore that the Bing independent float kit raised his mileage by about 3~4 mpg, but I never tried it.

    HTH
    mully
    #23
  4. Stephen

    Stephen Long timer

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    Theses last two posts....YES!...absolutely. Careful valve adjustment (do this first) and a good, complete carb overhaul are very good ideas. Bing says replace needle and needle jet every 20k miles, which is likely a tad extreme, but mine were in sad shape at 30k miles.

    All that stuff about the choke cover is true. And replace all the rubber bits--the idle mixture screw o-ring and such. And the diaphragms. Yeah, I know, you couldn't see any holes...if you have the originals, it's time to replace'em. Age is as hard as mileage on rubber.

    As to radical engine mods...raising compression probably does the most to improve fuel economy, and is the simplest path to improved performance.
    #24
  5. Mikey Monger

    Mikey Monger When pigs fly...

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    89 R100GS- Usually about 32mpg. It can get as low as 26mpg when I'm really hammerin' it or up to 36mpg when I baby it.
    #25
  6. Gringo

    Gringo simple by nature

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    Mine's a '92 GSPD with 52K on the clock, stock carbs, exhaust, etc. pushing a Parabellum windshield. I always burn high-test, though the bike doesn't seem to mind regular. I've had it almost 12 years and check mileage every time I fill up, and consistently get about 43 mpg for normal riding - loaded and two-up I get around 40-41. For awhile I was fiddling with the carbs trying to max out mileage, got into the upper 40's and was shooting for 50 until it gagged from fuel starvation when I tried to pass trucks on the interstate, which was unacceptable. At current settings it runs so nicely in all situations that I've accepted the compromise. Was getting ~45mpg before I removed the 'pulse air' system last year, but the idle smoothed out so much that I like it better this way - may have just had a vacuum leak with all that silly plumbing, but it stays off.
    I'm a fanatic about keeping the carbs balanced for ultra-smooth running and suspect this helps fuel efficiency too. Makes for a nice range - I always get at least 300 miles out of the left lobe and then start playing the right/left petcock game to get 3 reserves out of her; I've never run it dry but went 360 miles on a tank once, well into my second reserve and sweating bullets when I couldn't find a gas station open after 6pm in rural Montana; finally found an ag station open, run by Slim Pickins' twin brother, but that's a whole other story... Love that big tank!
    #26
  7. summerinmaine

    summerinmaine Hells Atheists MC

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    Thanks Gringo! It appears that our bikes are pretty equivalent, so unless you consistently run at very low revs, it sounds like I should be striving for a bit better mileage.

    Summer
    #27
  8. Gringo

    Gringo simple by nature

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    Yeah, your mileage sounds real low to me. I seldom ride below 2500-3000, like to be in the 3,000-5,000 range most of the time, so I don't think I'm babying it; and I just swapped plugs and mine were a perfect light tan color, very clean. Do you keep the carbs well balanced? If you have one side richer, the engine is probably not able to use all that extra juice with the other side limiting revs, so it just goes out the pipe; plus the bike is so much more enjoyable to ride when it's tweaked to perfection. I like spark-plug extenders better than vacuum for this - gave my Twinmax away after I did a few adjustments with it and was able to get a noticeable improvement on that adjustment using the shorting method. You might want also to check your mixture screws on the bottom of the carbs - I've found mine runs best if I'm not more than a hair or two off the recommended starting point of a half-turn out from seated; the bike will run with that screw just about anywhere, but a proper setting makes a difference across the entire range (cured my fuel starvation issues...). Also make sure your air filter is clean, valves correctly adjusted, tire pressures are good, blah blah blah...
    #28
  9. Jabba

    Jabba "HOLD THE LIGHT!!!"

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    ...and drafting behind a great big handsome guy on an 1150 helps, too~ :evil
    #29
  10. rlonstein

    rlonstein Simple by choice

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    I recently bought a 92 R100GS/PD (also fitted with Parbellum and bags) myself (thanks assrider :thumb, great bike) and ran a couple of tankfuls through it. A weekend of keeping up with the sportbikes on the twisties, twenty-odd miles of hard pan/gravel, three hours suffering in stop-and-go city traffic and four of hours in crosswinds on the slab highways still got me 34 mpg (same as my Honda CB750 when wringing it on fast backroads or slab with a head wind). I spoke with my brother-in-law out in California and he gets similar from his '91 GS. I'd expect mileage to go up with less exuberent and more steady riding.

    A valve adjustment and pulling the carbs probably wouldn't hurt. I'll take a crack at that this winter.
    #30
  11. deerslayR

    deerslayR Spodely Adventurer

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    Uh-huh, My PD returned 28 mpg during the Dead Horse Bean Run this past October. We were running up and down the hollers of Pennsyltuckey like a bunch of butt shot turkeys and I was glad to have that 9 gallon super tanker
    between my legs.
    Gonna rebuild the carbs this winter if it gets cold enough to stop riding. :lol3

    deerslayR
    #31
  12. Eurobiker

    Eurobiker Vintage Cat Herder

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    [​IMG]
    #32
  13. Possu

    Possu de-nOObed!

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    My old 94' airhead GS used to return somewhere in the mid 50's per (Imperial) Gallon or 4.54 litres. Best was 223 miles on 20 litres when I hit reserve, 200 plus was common before reserve.
    #33
  14. Malindi

    Malindi Zen Adventurer

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    Sounds like the mixture is a bit too rich. Small changes in the mixture make a BIG impact on an airhead's consumption.
    #34