Poor Mileage FAQ
by Kristian #562
Please read the Disclaimer before attempting any work in this FAQ.
This FAQ is ONLY about getting poor gas mileage. If you have a problem with starting or poor running, see the Hard Starting Poor Running FAQ.
Why is my mileage decreasing?
My bike’s mileage seems to be
decreasing. What is going wrong.?
A. It depends on a lot of things.
The FAQs below might be able to help you out, they are in no particular order, but try the simple things first.
Easy to Check:
Tyre pressure – See the Tyre FAQ. Some riders have gained 5mpg with the correct tyre pressures for their riding conditions.
Air Filter Condition – See the Air Filter FAQ. – Easy to Clean and has quite some impact on the mileage.
Idle speed set to 1400 rpms. Refer the Idle FAQ.
Chain Tension & Condition & Sprocket Condition – See the Chain FAQ.
Spark Plug Caps - See the Plug Caps FAQ for more details.
EPD Canister Canisterectomy FAQ. – Have you removed it, or removed it properly.?
Oil Condition – Poor Oil/Incorrect Oil will cause poorer compression, faster wear and could be the cause of a slipping clutch. You should be using FULLY Synthetic after the first 6000 miles (Note that BMW have a Service Bulletin which says to NOT use FULLY Synthetic. Semi-Synth is OK.). Oil Change FAQ
Spark Plug Condition/Mileage.
Are all your vacuum lines unrestricted.? See the Canisterectomy FAQ (The part on Vacuum Lines).
Are you just getting USED to the bike and driving it more robustly.?
Choke. Are you SURE you are using the Choke correctly. Is the Plastic Nut at the Carb Broken? (Very Easy to break).
Speedo Reads Correctly.
Medium to Check:
Valve Clearances – See the Valve Clearances FAQ for more details. Loose valves will cause lower mileage. Should be checked every 6000 miles.
Carburettor Condition particularly the Carb Diaphragms (Easy, can view from Top) or Venturi Jets (Inside the Carb). See the Carb Cleaning FAQ for details. More difficult to diagnose and to check, however does affect mileage significantly. "FWIW, I had holes in BOTH diaphragms and was still running 90 MPH with no choke. But gas mileage was in the 25-30 MPG range."
Check condition of Intake Rubber (Both Sides of Carb, but particularly into the head).
Carb Jet Sizes and Needle Clip Positions. See the See the Carb Cleaning FAQ. If you ought the bike used, someone else may have been fiddling around with the Jets, Needles and Float Bowls. See the Performance Modifications FAQ for details.
Exhaust (Catalytic Converter). If you put on an Aftermarket Exhaust this will affect your mileage. (Probably increase, with no other modifications)
More involved to Check:
Bike Mileage: Worn Valves, Piston Rings, Low Compression and Valve Guides will all contribute to low mileage.
Feedback on Reasons for Low Mileage:
Excluding tire pressure and weight, can anyone give me their top 5 reasons why one might get low miles per gallon?
Aggressive riding style - mucho in-city riding (stop&go traffic) - worn carburettor parts (if your engine has them) - dirty air filter - something the matter with the electronics if your engine is fuel-injected, veggie_deluxe '94 F650 -- Malmö, Sweden
1. Ambient Temperature 2. Speed 3. Type of fuel 4. Engine tune 5. Style of riding F650GS Dakar, Oregon. Steve 1130 Or
1. Heavy throttle and constant movement of the throttle. 2. High rpm, heavy loads and riding into the wind. 3. Worn or mis-adjusted carbs. 4. Fouled spark plugs. 5. Dragging brake pads and a worn, rusty, chain. A damaged carb diaphragm would hurt mileage, as well as power. Also a blocked or dirty air filter. My daughter once stuck a rag under the seat of her bike and it would partially block the air intake, occasionally and would reduce the bike's high speed power. Richard #230
Don't forget altitude! chppdlvvr 2001 F650GS, Aurora, CO.
With altitude, air density decreases, so a computer controlled fuel injection system will automatically decrease the fuel in the mixture to match the air density. Thus all the electronic sensors needed to keep the motor running correctly. You will find that horsepower will decrease, but mileage will actually increase. This is why airplanes fly at the highest altitude they are capable of. When flying a piston engine aircraft, you manually lean the mixture with a control knob on the panel after levelling off at cruise altitude, leaving it at full-rich while climbing for cooling effect. SScratch '01 Dakar -- Nashville.
I agree with Richard. I would however change nr4. to old plug caps (to high resistance) instead of fouled spark plugs, since that is the same thing as nr.3 (worn or misadjusted carbs). Just my experience. Regards, Spakur #1117, Icelander in Malmö, Sweden, 1995 Classic Red F650 with 65.000+ KM
Low compression? no other symptoms besides low mileage? wicked94pgt BBG#22
Gasoline Octane County '01 F650GSA. Memphis, TN.
Wind resistance (related to speed). Tall windshield, handguards, tank panniers, saddlebags, topcase. Bad carb diaphram(s). Pukin' petrol syndrome. Marty #436-Chicago-97 F650F.
1: (by far) wind and wind resistance due to boxes etc. 2: EFI unit is "safe mode" 3: speed - above 60mph/100 kmph economy drops off fast. 4: road surface (sand not so good, hard cold asphalt good) 5: measurement: e.g. the speedo or the fuel pump (very rare) are incorrect. y_kiwi
MINE would be: 1. Going too fast. 2. Carrying too
much crap. <- Oops... that's too much weight 2. Headwinds. 3. Too many UPHILL
miles and not enough downhill miles.
4. Too much wind resistance due to luggage. 5. Suck-a.s.s "oxygenated" winter fuel. Flash #412
My top reasons: * Prolonged stop-start riding * Incorrect use of gears (not changing up early enough) * Riding 'on the brakes' (not reading the road ahead) * Insensitive or excessive use of the Go-faster switch * Too many racing starts * Dragging brakes * Tyre pressures * Obesity .chiefkeefe Keith - Hampshire, UK -- '02 F650CS -- '71 Moto Guzzi Nuovo Falcone -- BBG#17, CG#1310
What Mileage should I be getting?
So, what sort of mileage should I be getting.?
A. This is a very difficult question to answer, because it depends on so many things which you as a rider control. These cannot be considered as “repairable” contributing factors to poor mileage. These are riding conditions, on/off road, around town, preferred rpm range, altitude, riding style, laden/unladen weight, choke use, modifications. Some inmates get 45-50, some 50-55, some 55-60. If you get less than 45-50 with a stock bike, normal around town riding on the road, and you have a high mileage bike, it’s probably time to check the Carbs. Same goes if you get less than about 50-55 on the open road.
those in the US: a UK (imperial) gallon is 4.55 litres. A US gallon is 3.79.
Which is 1 Imperial gallon = 1.2 US gallons
Thus, US mileage for a reported 50mpg (UK) = 50 / 1.2 = 42 mpg (US)
Classic” Funduro and F650ST.
Richard#230 has a Staintune but no other modifications, gets around 55-60 mpg, but he is an older gentleman, who drives in the lower rpm range and I believe very steadily, by all accounts. Flash#412 on the other hand, gets low 40’s when he’s really going for it or fully laden and up to mid 50’s when he’s cruising.
I've got a 94 Funduro and get better miles to reserve. Average is 205 miles, best was 240 at 60 mph on motorway. This works out to 60mpg to 70mpg. I've even put 15 tooth front sprocket on. This mpg figures have remained pretty constant from 17,000 miles on the clock I started at last November to the 35,000 I'm at now. r1speedyrider.
I'm experiencing avge 40 mpg on my ST. Best tank, 47, worst tank 34.5 MPG. I lust to have 55 MPG from my bike. Combined with my new 7.0 Gallon Acerbis, that would be about 350 Miles between stops! Makes me smile just thinking about it. Steven "scooter scum" Johnson.
MPG woes - need guru help. Okay, I am about to crash the server I have spent so much time going back and forth between my bike and the FAQs. Basically here is the deal:
I left Seattle in June with 13k on the bike, heavily loaded Touratechs, and an attitude. I got about 45-48 mpg riding fairly hard with that setup; I noted that that was about 10% below normal, understandable given the load.
Late in my trip, with about 23k on the bike, I noticed a precipitous decline in mpg, around 38-42 depending on conditions. so I changed chain and sprockets in Minneapolis, having noticed that the rear wheel would not spin real freely even after doing the chain clean/lube routine.
Still ended up getting at best 43 mpg.
So I get home and I proceed to:
- change oil (as had been done regularly and properly with synthetic 15w-50);
- replace spark plugs and air filter; replace and properly inflate new tires, checked bearings while I was at it;
- check valve clearances (they were in range);
- replace battery (which had dried out a few times but never failed);
- perfunctory check of carb needles and diaphragms which looked fine, and eyeballed float bowls which looked okay to my utterly untrained eye;
- and -- here's the fun part -- I put an ohm meter on my plug wires and the caps both looked fishy ... later a tech confirmed their gone-ness and BMW replaced both caps under warranty! eureka, he shouts, prematurely.
Tonight I rode 200 miles (27k total on bike), totally unloaded, not working it hard at all. my fill up at 156.9 miles took 3.628 gallons of gas for a whopping mpg of ... 43.25. this is only slightly above the _lowest_ reading I had ever gotten previous to my long tour; that was one tank of gas that sat in the bike for nearly 2 months of only short in-town commuting 4 miles each way to school and back, giving me 40 mpg (almost 2 years ago).
Okay, I mean this totally serious now, WHAT GIVES?
I've done everything the FAQ says except tear the engine open and look at
rings and valve seals, which makes no sense anyway given that the oil has been
kept religiously. (Note: Norm had NOT changed the Carb
Venturis/Diaphragms when he made this statement, ed)
** Given the above, why in the ^%$# would I now get a good 8-10 mpg less than I was getting 4 months ago?
** How can replacing demonstrably bad plug caps not improve performance (I did not experience any great increase in power or smoothness of the bike after replacing the caps)? oh, I also replaced battery and did a volt test with bike running, it is right in line with reports in the VR faq ... (never over 14.x volts at battery at various rpms)
** Which major part of the carb (Venturi?) is most likely to be the culprit here given that I have done/fixed/checked/danced over everything else?
**This is seriously pi**ing me off. it makes no sense, unless the unexamined carb part is the sole culprit; you would think that all of the crap I have done so far would have had some kind of additive effect to increase mpg at least slightly.
In the end Norm changed his Venturis + Diaphragms: Woooohoooo!! 55mpg!! Well, finally tore my carbs completely apart, and replaced: diaphragms, Venturis/needles, needle valves, seals and those crappy brass screws. The old diaphragms were definitively shot to hell; they basically disintegrated when I tried to stretch them for inspection. The Venturis were not wobbled-out in a tear drop shape, but once I got the new ones, I could see that the old ones appeared to be uniformly enlarged by a small fraction of a millimeter (i guess from vibration of the needles). the new needles fit noticeably tighter in the new Venturis. one old needle valve had an obvious stepped wear mark.
I ended up paying the tech across the street an hour labor to reassemble the carbs. he then sniffed the bike to get the best settings based on CO emissions. the bike now has a sick surge/stall issue at idle > < 3500 rpm (only when cold), but the tech's going to help me sort it out, gratis.
So, today I went for a rip on a cool but crystal clear day here in the Pac NW, and went 175.7 miles on 3.190 gallons of premium. that comes out to 55 mpg or so; this is a rebound from the 40 mpg I was getting with the knackered carb parts.
How many miles were on the bike/carbs when you did your rebuild?. 28.5k miles. What year "classic"?. 1999. What kind of environment has the bike been stored in when not in use? Outside but covered, in the mild Seattle climate (I.e., never super hot nor frigid cold) How often did you or someone ride it? At least weekly, except for last winter when I put it up for 12 weeks (using proper storage protocols, drain carbs/tank, etc ...) all kinds of use: city commute, touring, some dirt roads. The precipitous decline in mpg occurred while on my 13k mile trip this summer. NormJ #473
I get over 55mpg when riding solo with all kinds of 'gunning it'... and about 50mpg with a rider. 97 Funduro w/ 9200 miles. Omnikron.
Something to check, the choke cable goes into the carb and attaches to a brass type piston thing (a good tech term). Mine was gummed up and wouldn't go all the way to the off position. At the same time I found holes in both diaphragms. Each had a largish tear and a smaller hole. Charlie #070 from Pennsylvania.
If you are riding in states with oxygenated gas (MTBE or Ethanol) your mileage will go down quite a bit. This is why truckers hate oxygenated fuel. Its basically filler-you get less for more money. Check the rear wheel is not binding. It should just rub the brake disk but not be too stiff. It does have to move the chain and sprocket. See if the wheel is much harder to turn after braking a bit. Also, your rear wheel bearing maybe toast. I need to replace mine soon. My rear wheel doesn't spin as easily as it used to and the bearing felt a little notchy when I checked last. Justin843.
My '99 with 18,000 miles on it routinely gets 40-42 mpg (depending on speed). When I first got the bike, I got 50 mpg. I attribute the drop to: 1) getting used to the bike and riding faster; and 2) wear in the slide needles and Venturis. My low speed jets are adjusted to just less than 3 turns out, and it still runs a tad rich, if anything. For my bike, 3.5 turns out is just too rich. I'm not going to tear into the carbs until the mpg drops below 40. Bob#550 (Olympia WA).
Hmm, 43mpg is about what i calculated during my trip this summer, I kind of expected more, but its a big step up from the 15mpg or so I get in the SUV. Will K, TX
IMO 43mpg isn't bad, nothing I would even consider taking the bike apart for, expectations of major performance improvements based on minor increased resistance in the plug caps is unwarranted, and I didn't see you mention FAQ's regarding worn emulsion tubes. Todd #389.
Slow down. You mileage will go back up. You're getting used to the bike and because of that you are going faster. Running 85-95 mph (WFO) fully loaded, I get 35mpg. Running 75 mph with the same load... 44 mpg. 43.5 is NOT bad mileage. I'm HAPPY when I get that. Flash #412 (CO).
I only get around 37mpg, but most of my riding is stop-start city, with 75mph highway miles sprinkled in. I think mine also needs a carb adjustment, and it is running a bit rich. Mason #631 - 97ST in PA.
Flash makes a great point. WFO highway cruising uses up a lot more gas than you would think given that mpg ratings for cars always give a city/highway that makes it look like you should get better mileage on the highway - but 'taint necessarily so. Try riding the same route at or near the posted speed and then again at the speed us regular human beings ride - you should notice a significant difference in fuel consumption. On the other hand, pull and clean the carbs too - it is actually easier than you might guess when looking over the FAQs and IMHO a damn sight easier than checking the valves! (Just remember to pull the hose clamps as far back on the rubber as they'll go before inserting or removing - it makes a big diff - and remember Flash ain't joking about the usefulness of Astroglide etc in the process), it's a good exercise and getting fresh o-rings, needles, jets etc isn't too expensive. Sean #1015 Ottawa Canada.
43 ain't bad at all the drop can probably be blamed on worn needles and inserts, big singles do shake a bit and the soft metal of those parts can't take it forever you could try raising the clips on the needles one notch will cure it for awhile till it wears a new spot on them,,,,just remember slightly rich is good, lean is bad! mike410(Iowa).
I get between 45 and 55 (driving at 60mph) mpg after I changed a lot off stuff last spring (se the carb cleaning FAQ for info). Spakur.
42 mpg was the best I ever got, down to lo/mid 30s on last trip. Carb rebuild parts are in the saddlebag...all I need is the time... (at 25K miles right now) . Marty #436-Chicago-97 F650F
I have a '02 Dakar, and always enjoy 70-72 mpg when I cruise at about 55 mph average speed. I get about 62-65 mpg when cruising at about 60-65 mph. It drops to about 52 mpg at 75+ mph. I get a low of 50 mpg around town. My wife tells me our monthly gas bill has been reduced to about half what it was before I bought the bike. Scott, ID
Records. According to my Records for the Classic, with Staintune and a 135 jet,
I got average 42mpg, but when I started at (and went back to) stock it went up a
bit to about 47-48.
Kristian#562 HK ex'96F, '00 GS.
55 mpg round town, up to about 75 on a decent run if you take it steady. Don't know what that works out at in US gallons. Andy Leeds UK #982.
40 miles per US gallon if you flog the snot out of it. Visit the FAQ for a wealth of info about your new steed. Welcome to the Chain Gang. Consider supporting the endeavor here by joining. Flash #412 (CO).
Our 97 F650ST gets just over 50mpg. DaveJ#888(Hannibal,MO).
My '97 gets 41 driving around town. When flogging it, or holding 80 mph on the freeway, it drops to 39. YMMV! Scott LS
I, personally, prefer not to FLOG my bike. But I do like to RIDE HER HARD! Riding her hard, I find I get around 40 mpg US. In the winter with an extended warm-up (<30degFar), I've gotten 34.Shawn #1051 Maine.
I get 50 mpg around town and about 54 mpg on the freeway (at 70 mph) on my 1997 bike. No flogging, though. Richard #230, Pacifica, CA.
I get about 50 mpg around town or on the highway, except when cruising at 75 to 85 mph with my 2000 Funduro. Leo #699 Utica, NY - 2000F
My classic '97 gets between 40 and 45mpg, no matter how I ride it... Robert #959 in TX - '97 F650
Yup, about 45 mpg commuting on my '99F on a mix of secondary & HW miles. I usually have top box & saddlebags mounted. No flogging. About 215 lbs total rider & gear. Andy #618 (MD - '99 F650))
I've got GIVI bags on the 1999 Funduro and get almost exactly 40mpg. There are a lot of very hard winds lately here and I weigh almost 240. Joeg #1102 -Fremont, CA.
Fuel consumption. I recently bought a 2-year old F650 Funduro. It round out of fuel after 80 miles. Admittedly this was riding through congested city streets. But it seemed low to me. My BMW dealer said I 80-100 miles around town sounds about right. Martin, London, England
150 miles is about the least you should get on a full tank. Your dealer is either uninformed or lying. Consider finding another dealer or else use the FAQs to take care of the bike yourself (preferred). Flash 412 (CO)
Dunno about the UK, but in the USA in the winter they add "oxygenators" to the fuel. Fuel prices go up and the energy content goes down. So not only do we get to pay more for fuel, but we get to fill up more often, too. Supposedly it reduces air pollution. Unfortunately, one of the oxygenators, MTBE, does whatever it does at the expense of ground-water pollution and increased cancer rates. Meanwhile, it hasn't been proven that MTBE causes any improvement air quality. Flash 412 (CO)
All factors, for me, considering partial highway (with/without traffic) and city riding. I go around 140miles before I fill her back up...upon fill-up at that point she usually takes about 2.43 gallons. With the prevalence of stations. Why not. MPG on the bike is not critical to me. It sure as h*ll beats whatever I am getting from my truck...the difference between a 5$ fill up and a 25$ fill up make all the difference... However, I have had the bike sputter and stop at 100 miles and had to go to reserve...I need to check the screens before I blame it on anything else...I have not done a Canisterectomy...as yet. Nick #1085 Glenwood NJ 07418. 99 F650
Donna and I on our 99 and 97 F650 regularly go to 170 or 180 miles before filling up. Have gone to a little over 200 miles before filling. Get about 50 mpg all the time on regular 87 oct. gas. 99 F650(mine) & 97 F650(Donna's) Dave #888, Hannibal, Mo
I regularly got 40 MPG (US gallons) which was considered pretty low by most. I wrote it off to lots of frontal area (+6" windshield, tank panniers, topcase, etc) and the great flatland. At the end of the summer, the mileage began a greater slide, to occasional upper 20s/low 30s. Recently rebuilt the carbs, and found two torn diaphragms, two mis-adjusted floats (too high), and the mix screws at 2.25 turns. Unfortunately, looks like it'll be spring before I get to find out how much improvement I'll gain. Look in the FAQs under carbs. Marty #436-Chicago-97 F650F
Many factors are associated with fuel consumption, as you know. With my carburetted Funduro, I'd get about 45-50 mpg. The fuel injected bikes will give 60-65 mpg, depending on how hard you trash 'em. Fuel is the least expensive cost involved with riding--- depreciation and parts are the most cost, IMO. Steve#1059
Commuting in DC traffic on my '99 F I've gone as far as 186 miles - I usually top off at 165 so I'm not caught short. Something is wrong with your bike. As Flash said, the FAQ is a good spot to start. Andy #618 (MD) 99F
UK carbed F's have no canister. The fuel is the same summer or winter (you actually get more for your money if the tanks are colder!). My 99 does about 50 mpg round town on a bad week in the cold. Winter makes it worse as the visibility (freezing fog today) and road surface (covered in Diesel) prevents you making progress steadily above car speed. Take in into the hills for an hour and you get 75 mpg. I'd change the oil and filters, use some carb cleaner and if you don't have an inline fuel filter, get one. If the range is a problem you can still get the Acerbis tank (200-450 miles). Andy Leeds UK #982
50 mpg is about 270 miles with the Acerbis tank. I can't remember what the standard was (17 litres?) but I'd guess at 170 miles. Andy Leeds UK #982
I reckon I'm getting about 39mpg (UK) 32 mpg (US). But I'm only getting about 8 litres in the tank between refuels. The tank capacity is 17.5 litres. Martin
That is a bit low. Maybe a tune-up is in order. I was getting 50 mp US g around town and recently dropped to 47 mpg, when the winter smog gas arrived. At a steady speed on the freeway, I get around 55 mpg. Richard #230
Okay, I've visited the FAQ on gas mileage, but I'm a little concerned about my '99 ST. It's got 17,000K on it and I'm experiencing 30 mpg in the city (35 if you use Imperial gallons). The last tank was about 25% highway, the rest was very short (3 km) trips to work and back. I got only 195 km before I hit the reserve. My driving is fairly moderate, I don't exceed 60-70 km/h too often and I'm usually not gunning it to get up to speed. My tire pressure seems okay, and it was serviced just before I bought it in January so I'm assuming the engine is in good order. The dealer I bought from is reputable and I trust that they've done their part. The other part of this is that I'm a new rider, so maybe I'm shifting at the wrong times? I generally wait until the Tach is at about 4K before I shift up, is that too soon? I worry that I'm revving the engine to high. When I slow down to stop, I generally don't use the engine to slow me down, I just clutch and brake - shifting down as I'm slowing down, but not engaging the engine. Vancouver650ST '99 F650ST.
Well, I believe the '99 is still the carburetted bike, if this is so you should check how you are using the choke. I made this mistake when I started riding my '98 classic. I would slowly push the choke away from me after riding a bit, the bike would then stall so I assumed it was not warmed up. What it turns out my problem was is that I was assuming the choke is progressive, it is not it is basically an on-off switch. If you ride with the choke on you get milage approximately around where you are. once I figured it out I get more like 50 MPG and I like to hit 80 MPH on my morning commute. If this is not your issue check the FAQ as there is a section on poor fuel economy that gives a list of stuff to check from easiest to hardest. MasterITRIT #F650-1231, '98 F650 Classic
I ride much like you do and get 50 mpg (the small US version) around town and about 55 mpg on the highway at 70 mph. My bike is a 1997 model and has over 30,000 miles on the clock. My guess is that your carbs have either been rejetted richer by a previous owner or are in need of a rebuild. But check the easy stuff first, such as replacing the sparkplugs and checking the carb vacuum rubber diaphragms (which can be done with the carbs on the bike) to make sure that they don't have any rips or holes in them. When you check the diaphragms you can also check the condition of the needle and the position of the needle clip. Of course, also check the air filter to be sure that it is clean and check that the "choke" turns off when you push the lever. Richard #230
Well I am 225 (lbs) on a good day. I also almost always ride with the City cases with rain gear and some tools etc. int hem. I would say that is close to your frame, I have also often ridden with my top case with lots of stuff (even a Dutch oven which easily puts me over 240) and I have not noticed too poor gas milage from that maybe I average 45 mpg. how tall are you, but I don't think wind resistance could make a difference of 15 MPG. I am 5'8 also on a good day. I definitely ride her hard, I am always twisting the throttle and have had her in triple digits on more then one occasion. I average 80 when touring around (well the cop said it was 77 in the 55 zone and I did not argue, and got out of the ticket anyway ;-) MasterITRIT #F650-1231 '98 F650 Classic
Well, I just ran through my first tank of gas on my newly acquired 1999 model. It got almost exactly 40MPG with a good combination of highway and twisty travel. That seems a little low to me. What are other carburetted inmates seeing? Joeg #1102 -Fremont, CA.
My 99 F650 with 28500 miles gets about 185 mile range to a full tank, that's with the reserve used up, I flip to reserve at around 140-150 mile mark. cat0020 #1056
I get between 50 and 55 mpg, depending upon the type of riding that I do. Richard #230, Pacifica, CA
I figure out my mpg pretty much every time I refill normal city/suburban commuting (avg. 12 mile rides): 45-50 mpg the worst I ever get is about 40 mpg and that was when I was riding only in the city avg. 2-3 mile trips Tom (Maryland)#773
I also have a '99, and with 23,500 on the clock and I get 40mpg or less. I do LOTS of city riding, lots of lane-splitting in first gear @ 5000 rpms, and ride generally ham-fisted. Shank
I got 45-50 with my 97 until I opened up the airbox, added a K&N filter and raised one needle one notch. Now I get 40. I am looking into finding some needle shims so that I can raise the needle less than one notch. Chris in Santa Cruz, CA #782
My 97f gets about 45mpg: daily 30mile round-trip commute on rejetted carbs, and I will say I flog 'er. I think it was closer to 48mpg when it had std carb settings. you may want to see the FAQ and see the rejetting spreadsheet for a comparo of various configs. tom 
I get from 40 to 50 mpg with my '99 F, depending on what I'm doing. A moderately slow (45-60 mph) ride in traffic on a two-lane gives me 50+. Having fun in the twisties and commuting around town gives me 40, or a little more. It seems my mileage has steadily gone down since the bike was new (at 14,000 now). I give much credit for this to my own right hand; and the rest to the carb needles and seats wearing. Bob#550
On our 97 F650ST we get about 50-52. On a 99 we had previously, we got about 50. DaveJ#888(Hannibal,MO)
F650ST with 20k miles: City riding: 41 mpg Backroads: 53 mpg Bike guzzles less with 89 octane than Premium. On some other Ganger advice I filled it with 87 octane for the first time two days ago.. I'll see. Jean #636
Drop in gas mileage. I usually got about 210 miles
per tank on my 97 F650ST. I'm now getting about 150 miles per tank. Any input on
reasons (excluding speeding). '97 FT650ST. I have checked the pressure and
cleaned my air filter, changed the plugs and checked the valve clearances. This
is over a period of 15 tanks of various gas.
I have noticed that my mileage has been dropping as my bike gets older. I believe that it is a combination of general carb wear (mostly needle wear) and the new blends of smog-gas, which have less gasoline and more other things that don't burn as well in the mixture. My recommendation is that you try replacing the carb needles, which are very easy to do by just removing the top of the carbs. Assuming that your air filter and spark plugs are clean and there is no unusual drag on your wheels, that should help. My mileage has dropped from 55 to 50 over the past 6 years, but that still isn't low enough to motivate me to take action. Richard #230: 1997 Funduro, 2002 R1150R, 2002 Yamaha YZ1, 1993 Honda CB750 - Pacifica, CA, USA
If you want to see what sort of mileage some people are getting after a new exhaust/rejetting, see the F650 Exhaust Rejet Spreadsheet.
GS and GS Dakar
See the Fuel Tank FAQ GS
What is the Range of the F650?
See above for Mileage, but in General:
About 380 km on the standard Funduro European tank, 500 km if you are an angel with the throttle. The Touratech tank pushes this out to 520 and 660 km respectively. I have done 420 miles on the Touratech tank (680 km) but I was a bit stressed on arrival at the North Cape, had emptied my stove into the tank and was coasting down all the hills. I put 26 litres in a 26.5 litre tank at Skarsvag (you need a mortgage to do that)! Bike averaged 71 mpg in Norway, but speeds are low. 55 mpg is typical UK mixed running. Standard tank is 19.5 litres (4.33 Imperial gallons, ??? US gal.). Andy Leeds UK #982.
What does 50mpg translate to in terms of range? The tank (classic) holds 4.62 gal. per the manual. That would be about 225 miles plus a little to bone dry. Dave 99 F650(mine) & 97 F650(Donna's) #888 #888A
See the Fuel Tank FAQ GS
What About Ethanol in the Gas?
Q. I see in my latest Motorcycle Consumer News that all of the major oil companies in California, except Chevron Texaco, will be removing our beloved MBTE from the gas in California next year and replacing it with ethanol, to produce a new and improved smog gas. Does anyone know what this is going to mean to our motorcycle engines? Are they going to run better or worse? Are rubber parts going to dissolve faster? Inquiring minds want to know what will be in store for us next year, besides higher prices and fuel shortages. Richard #230, Pacifica, CA
It's CORN you guys and we have been running it in Iowa for years was a big rhubarb when first started but it actually makes NO DIFFERENCE to a late model bike. Both of our 99 F 650's run just fine on it, Gas milage is as good or better that "straight" gas it may dissolve some crap out of older cars and bikes with metal fuel tanks and plug some filters at first but that stops after the first few tankfuls and then should be fine. I run the stuff in all my old bikes and have had NO problems with rubber parts going to hell. Maybe if you guys out west burn it too we may get more than 3 bucks a bushel for corn. Mike410 (Iowa).
the gas tank won't be much of a problem (Dri-gas is basically 2-propanol, i.e.,
isopropyl alcohol). Do you have any specs on what the percentage of ethanol will
be? I would imagine that if you filled your tank with the bike nice and hot
(Classics only, no idea about them GSs and Dakars) and then let it sit in the
nice hot sun, getting heated from above (sun) and below (engine heat), the
ethanol would evaporate rather quickly. I don't think the ethanol will do much
to the various O-rings it will contact. Could cause some swelling, which may or
may not be a good thing.
I think it will mainly cause starting problems, low rev sputtering and generally bad manners. But the Merck manual states that it's an octane booster in gasoline, so maybe it'll make the bike run better. Incidentally, every winter I pretty much put isopropyl alcohol into my tank at every fill-up to avoid water in the gas tank problems. I put it in at about 0.0025% (50 mL in 20 liters). Never had a problem. Of course, ethanol isn't the same as isopropyl alcohol. But similar enough. I'm sure since this is a CARB dictate, it'll cause ALLLLLLL sorts of problems. Shank NYC USA