I don't frequently care about the MPG of my GS but I have noticed over the past few tanks that it might be much lower than I expected.

Some get >50mpg on a GS, I am guessing on an F model with lots of 6th gear 50mph cruising and with the 3-circuit carbs.

But few report <40mpg and it seems that I am regularly getting the 30s.

The trouble is that it is difficult to always fill the tank to exactly the same level, or even close, and I figure there's +/- 1/2 gallon each time which is a lot. But yesterday I put in almost exactly 4 gallons and it was 140 miles, 35mpg. This has been pretty consistent.

What do we think? too much main jet? I have 125s and the original 122.5s here. Bike runs basically perfectly but it's possible it's rich with the 127.5 jets. Would that explain poor mpg?

BTW probably 70% of my riding is sort of suburban commuting with stop-and-start traffic, occasional hilly 60mph stretches and part windy backroad 40mph. The other 30% is neighborhood/back-road/sub-45mph. I don't ride like a hooligan and I don't do high speed highways.

Over the last few tankfuls I've managed about 60mpg (40mpg with 3.7litre gallons) with a mix of in town, 60mph stretches and some 30s. mostly in 5th and 6th with a bit of hard acceleration here and there. All of that in ambient 20ish `C.

Thats with 115 mains and 40 pilots. if anything its slightly lean too, the plugs are 'too' white. its going to 125 mains tomorrow and a touch more idle mix.

Maybe its leaking fuel? or try for a different petrol station. a few years back my car went from 40mpg to 25mpg but filling with 97ron (I think thats your 95, our normal is 95 but I think thats closer to your 91) put it back to 40. after a few months I went back to regular and it was ok. other people nearby reported the same thing. duff petrol maybe, the car never felt like it was down on power just very thirsty.

It's possible you've seen some mpgs in UK gallons rather than US gallons - I average about 50 miles per UK gallon, which according to Google is roughly 40 miles per US gallon.

30 US mpg in stop-start traffic sounds like it might be about right - I think in the depths of winter, when I also lived more inner-city, 40 UK mpg (so down in the 30s US) wasn't extraordinarily bad due to all the filtering through crawling urban traffic. My current commute is a 9 mile motorway commute into the city with an average speed of 30-ish mph and far less acceleration.

Edit: that said, I just checked my mileage out. I filled it up with 10.8 litres today with about 140 miles on the clock, which works out to about 58 UK/48 US. As for filling the tank to the same level, my rule is to basically get as much fuel in as I can on the sidestand, so I can measure my mileage reasonably consistently. I guess if you fill it on the centre stand you've got to think about leaving some room in the tank.

I think I have been getting routinely 35-40 mpg with US gallons, but like you say, I fill it as much as I can on the sidestand except that I try to quit before it begins to splash too much gas out onto the paint. We don't have those funky Euro/California fuel nozzles that cover the inlet.

It's not bad enough that I am planning to pull the carbs JUST to change the jets down a size. Wait a minute, I bet I can change that jet by just pulling the float bowls.

I still think I need a smaller main jet and maybe a washer on the needle to get the bike to run more right.

But it sounds like 35-40mpg US is not awful.

switch to UK gallons for better mpg seems the easiest thing to do

I haven't checked mine for a while, but when I do I usually just fill the tank to the top while on the side stand, reset the trip to zero and repeat. I have a standard 2009 F, no mods whatsoever.  Just in case I usually do it three or four times which should even out any over/under fillings. I get about 75 mpg (UK) on a run, which for me is non-highway/motorway/interstate, but not around town either. So say mostly 100 - 110 km/hr with junctions every 10kms or so.

One thing I would do is to pull the plugs and check the colour - a nice biscuit brown tells you that the mixture is about right. Too rich (darker brown) tells you that the mixture is too rich.

Good luck.

Quote from: tobyd on June 15, 2018, 01:00:27 PM
switch to UK gallons for better mpg seems the easiest thing to do

Yeah, good plan! I suppose then Bob will be my uncle.

Quote from: barry905 on June 15, 2018, 02:51:54 PM
One thing I would do is to pull the plugs and check the colour -

yeah with modern fuel I have found that doesn't tell you that much.

My plugs are black on the rim and tan on the electrode no matter what I do.

If not that then Robert is your Father's brother at the very least.

I think plug colouring isn't entirely junk these days, whilst I can't get the plug rim to be anything but black the insulator goes through various colours, just not so impressively as the Haynes manual depicts.

not leaking fuel into the sump?

If it's not leaking it could be a problem with your right hand....

75 mpg?! I'm not even sure my old 125 scooter got that kind of mileage. Although junctions every 10km sounds like you hardly ever have to slow down, so maybe that would explain it.

Quote from: alpo on June 15, 2018, 03:48:44 PM
If it's not leaking it could be a problem with your right hand....

I dunno, when I ride I'm not exactly hypermiling!

For a more accurate picture of fuel consumption I'd start using the Fuelly app.

Essentially it's every time you fill up you note the mileage and the amount of fuel you add.  Over time you get a good average.

Of course filling the tank consistently is basically a requirement.  For the purposes of the test you could "bury" the fuel nozzle in the tank, let the auto-shutoff do it's thing, and make more frequent stops.
I usually fill to the bottom of the filler neck of the gas tank every time I refill.

I have a 2010 GS with the 3 jet carb, running stock exhaust and stock air filter. Using the km/litre to US mpg conversion charts 40US mpg would be the absolute minimum I would ever get and that's only happened once, to get that bad a milage I'd be on the highway fanging it at 150 to 160 km/hour between 7 and 8k rpm,  or riding in the 7 to 8k rev range doing the boy racer thing in the twisties, doing a sedate steady 100 km/hour on the highway I'll get 60 USmpg my usual milage though it 52 USmpg. My record is 323 miles on a full tank including reserve.

So yes there's some problem with your bike. I recently changed from the stock 17 60 130 to 20 60 132.5 and I did not notice any appreciable difference in milage.

I put my bike on the side stand and fill it so that the petrol covers the low side of the filler neck and almost touches the high side of the filler neck. I have also discovered that this tank does not have 4.3L reserve but instead has a 5.3L reserve, although the total tank takes 20.3L, I get 70 miles on reserve!

Quote from: mr72 on June 15, 2018, 06:28:51 AM
I bet I can change that jet by just pulling the float bowls.

But it sounds like 35-40mpg US is not awful.

Don't kid yourself 35-40 is a big problem. If you've got the Allen bolts on your carb then yes you can get to them via the floats, but I'd still take them off.

Quote from: user11235813 on June 15, 2018, 08:41:36 PM
I have a 2010 GS with the 3 jet carb, running stock exhaust and stock air filter. Using the km/litre to US mpg conversion charts 40US mpg would be the absolute minimum I would ever get and that's only happened once, to get that bad a milage I'd be on the highway fanging it at 150 to 160 km/hour between 7 and 8k rpm,  or riding in the 7 to 8k rev range doing the boy racer thing in the twisties, doing a sedate steady 100 km/hour on the highway I'll get 60 USmpg my usual milage though it 52 USmpg. My record is 323 miles on a full tank including reserve.
...
Don't kid yourself 35-40 is a big problem. If you've got the Allen bolts on your carb then yes you can get to them via the floats, but I'd still take them off.

None of your use cases include suburban/urban traffic, though. Depending on how bad it is, that could slaughter fuel economy, probably especially so if you live somewhere filtering is illegal and you have to sit in that traffic (so anywhere in the US outside of California, I think?). Traffic here in the UK is pretty awful - in the cities cars averaging only 10 mph/15 kph at rush hour is common. We can filter, but the repeated heavy acceleration that involves still kills your mileage. It's probably not that bad where mr72 is, but still. I don't think 40 mpg for a rush-hour commute on busy streets necessarily indicates something wrong with the bike.

@Kookas,

My normal use case is 22km/l which is 52 US mpg, 18km/l (42usmpg) is continuous 7.5 to 8k rpm fanging, 28 km/litre (65usmpg) highway cruising at 90-100km/hour. We do have filtering here but then that will be mitigated by me redlining through the gears up to the speed limit when I take off which is normal 22km/l including lots of stop start and short burst trips to the local shops. Under 40 USmpg is definitely an indication of something up. I get better milage than the gf's 650 Savage under the same conditions.

Quote from: Kookas on June 16, 2018, 03:54:08 AM
especially so if you live somewhere filtering is illegal and you have to sit in that traffic (so anywhere in the US outside of California, I think?). Traffic here in the UK is pretty awful - in the cities cars averaging only 10 mph/15 kph at rush hour is common. We can filter, but the repeated heavy acceleration that involves still kills your mileage. It's probably not that bad where mr72 is, but still. I don't think 40 mpg for a rush-hour commute on busy streets necessarily indicates something wrong with the bike.

Yes of course "filtering" or so-called "lanesplitting" is not allowed here.

Austin suburban traffic is probably somewhat unique among American cities. The city of Austin has had a war on effective transit for 2.5 decades now and they are winning.

For this last tank of gas it was probably 25% sub-40mph kind of neighborhood streets and no traffic errands, 2-mile-at-a-time trips. The rest would be this Austin suburban traffic which is like 2 miles of neighborhood surface streets, a couple of long traffic light stops, then a 17 mile stretch of about a 50/50 mix of 60mph and stop and start. Like, it'd be maybe a mile on 55-60mph road with a couple of traffic lights then two or three miles of stop a long time, then accelerate up to like 45mph, then stop a long time, etc., then a couple of miles of faster, less frequently interrupted stoplight, 60mph, stoplight, etc., and then a 5-8 mile stretch of truly miserable stop and go, but like on TX highways, the "go" is like accelerate and try to get going quickly so you can maybe make it through that next traffic light before it goes red.

My sub-20-mile commute takes about an hour on average. There's a road where I'll get going >60mph at times, so as you can imagine a 20mph or so average speed with 65mph peaks is a genuine mixture of fast and stop/start.

Oh yeah and my commute involves a big hill that's like 1/2 mile long and probably a 5% grade or more each way which frequently has stop/start traffic.

Now that I consider it, it sounds like 35mph on a carbureted motorcycle under those conditions may not be that bad. But I'd still expect to get more like 40.

I need new fuel lines so I might order a length of tygon hose and then take a Saturday morning to swap those and while I'm at it pull the carbs. Heck, it's been 3K miles or more since I had them off so it might be a good time for some light cleaning anyway. I'll go down one size on jets then (probably back to either 125s or 122.5 depending on what's in there now, I can't remember) and put a washer on the needles.

Running on reserve 24/7

I get about 150miles on a tank REALLY stretching it.

2006 gs500f (totally stock, 15,000 miles)--mid 50s US MPG around town. Just about the same on the open road (I go too fast). My Chevrolet Spark (standard transmission) gets 35 mpg around town, so it seems to me that a GS500 should get at least 45 MPG.

Quote from: J_Walker on June 16, 2018, 09:00:27 AM
Running on reserve 24/7

I get about 150miles on a tank REALLY stretching it.

What is this nonsense, on a 20.3 litre tank that is less than 12km/litre. That is less than 28 US mpg!


Yes of course "filtering" or so-called "lanesplitting" is not allowed here.

@mr72 Just to be clear, they are two different things. Lane splitting is what we call people who split lanes in normal traffic that could very well be on the highway going at over 100km/h and usually is on the highway because of the wider lanes.  However where filtering is legal as in Queensland, Australia, is only for traffic that is either not moving at all, or is going at less than 30km/hour. It allows bikes to filter their way to the front of the queue where it is safe to do so. It is very handing on non moving or heavy traffic on an expressway as you can ride on the hard shoulder. It is also allow between lanes but it not allowed between an outside lane and parked cars or in bicycle lanes, however (I've never let that stop me).

I think actual lane splitting is a very unsafe practice in fast moving traffic.

128 miles on 10.41 litres for about 56mpg old money, 45 new. Mix of commutes and aimless evening riding around. Gone down about 4mpg since switching to 125 mains but I have been giving it more beans as a consequence. going to try and hypermile this tankful.

£13.42 ($17.71) for the privilege so thats £5.85 a gallon UK or $6 a gallon US.

FYI just closing the loop on this thread:

I went chasing a stumbling issue (separate threads about this) and wound up switching the jets down from 127.5 to 125 and shimming the needles a notch, riding about 50 miles, then swapped the non-stock needles for stock needles with no shims, and rode another 50 miles.

For that 99 miles, I got <43mpg. After 99 miles I put in 2.3 gallons. I was ordinarily refilling at about 130 miles and putting in about 3.6-4.0 gallons for under 35mpg. This is a huge improvement.

I anticipate one I go through a tank of gas with the 125 jets and stock, unshimmed needles I'll probably get >45mpg. I'll report back here once I have a number.

I think the bulk of my poor mpg was being jetted one size too rich. Then a part of the problem was the non-stock needles with more aggressive taper in the midrange (richer). Both of which contributed to the stumbling as well so I fixed two problems at one time.