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Old 09-27-2004, 04:15 PM   #16
TEXASYETI
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91 PD, staying at about 4,000 or 60 mph gets me 42mpg.
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Old 09-27-2004, 07:51 PM   #17
Cpt. Ron
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I consistantly get 34mpg while on the highway and twisties. Cruise speed is usually above 5500 rpms. In the dirt and other slow going, it climbs to 40-ish.

There was some discussion on the airheads mailing list a while back about the fuel economy of the GS's. At least one lister claimed to have a big increase in gas mileage by switching to the 40mm carbs and larger valves (Euro spec) as well as upping the compression ratio (dual plugging too?). Sounded interesting, all BMW parts.....
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Old 09-27-2004, 08:58 PM   #18
clang
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Currently 35-38 mpg on the '92GS with 22k miles - no carb rebuild yet - 33 -35 on the '90PD with 47k and a carb rebuild about 10k ago........

These are average over all kinds of riding. I track it with every tank of gas on all my vehicles - can be a good early indicator of problems. I think you're in the range. A valve check/adjust and a careful carb sync may bump you up a few MPG......
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Old 09-27-2004, 09:38 PM   #19
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A great resource! Thanks for all the comments. Sounds like my issues are more behavioral than mechanical.
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Old 09-27-2004, 10:54 PM   #20
gaspipe
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My '94 R100GS gets about 36MPG +/- 2MPG depending on how I ride it. It's sorta disappointing, but it's a great ride anyway. I love the bike. It's got that Briggs and Stratton technology thing going on , yet it has nice torque. Maybe it's time to experiment with some Mikunis.

These bikes sound great with a Supertrapp pipe, if you can find one.

I find myself riding the F650 Dakar a lot these days since it's getting almost 70MPG.
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Old 09-28-2004, 12:44 AM   #21
Tim McKittrick
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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!
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Old 09-28-2004, 05:08 AM   #22
JamesJWeg
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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.

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Old 09-28-2004, 07:03 AM   #23
Mully
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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.

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Old 09-28-2004, 09:30 AM   #24
Stephen
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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.
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Old 09-28-2004, 09:51 AM   #25
Mikey Monger
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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.
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Old 09-29-2004, 08:08 AM   #26
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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!
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Old 09-29-2004, 10:19 AM   #27
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Quote:
Originally Posted by Gringo
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.
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
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Old 09-29-2004, 12:17 PM   #28
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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...
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Old 09-29-2004, 12:43 PM   #29
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...and drafting behind a great big handsome guy on an 1150 helps, too~
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Old 10-01-2004, 11:26 AM   #30
rlonstein
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Quote:
Originally Posted by summerinmaine
Wondering what the normal range is for gas mileage on the big airhead. I've searched the archives, but results were inconclusive (too much oilhead data).

I recently bought a 92 R100GS with a PD tank, and was surprised to see that my range is lower than I expected. I recently ran a test on a one day ride (one up,
I recently bought a 92 R100GS/PD (also fitted with Parbellum and bags) myself (thanks assrider , 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.
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