Poor Fuel efficiency

[Slycox]

Mornin,

I have noticed that I am still getting poor Fuel economy on my bike, it's better by about 6mpg than last year but I'm still getting about 27mpg. The carbs have been cleaned as per the tutorials and synced with the carbtune. When I checked the float height it was off about 2mm across the board And I did correct that. Not sure what else to check. If there is something that I need to do.

I will be pulling the carbs and cleaning again and double checking my work making sure I didn't miss anything.

Just wondering if there is another cause to this.

What had been done:
Carbs cleaned and dipped in Berryman's
New orings throughout new intake boots and orings.

Still needed as far as I can tell:
New air filter (I forgot I hadn't done this yet)

Thanks in advance

[Buffalo Bill]

Maybe the previous owner replaced the main jets with a larger size, thinking that would give it more power?
You can check those, and maybe replace them with the standard size.
Does it have the standard OEM air intake box and filter?
Again, many a silly man has removed those and replaced them with pod filters.
One guy can't beat all the man hours and testing the factory design staff puts into a bike.

[Slycox]

I'll be double checking the Jets and all that again.

OEM airbox installed.

[terrylee]

Don't know if it will help mileage but should adjust valves. Also did you sync carbs that should help.

[Slycox]

Forgot to mention that I did adjust the valves and new petcock.

And yes carbs were synced

[Buffalo Bill]

Well, if your bike is all stock, than something is wrong, it may be;
gas sucked in through the petcock vacuum hose?,
Carbs set too rich?
main jets too big?,
tire pressure low?,
brake shoes dragging?, check the calipers maybe one needs overhaul,
Slipping clutch?, replace discs and springs

[1980GS1000E]

Check if the carb vent tubes are are routed incorrectly. They should end above the float bowls.

[Steve]

Check if the carb vent tubes are are routed incorrectly. They should end above the float bowls.

Really? Never heard that one before.

I just checked all four GSes here, they ALL end below the bowls.

I just got "Junior" going last weekend, tomorrow will be the first long-ish ride to check mileage.

When Mrs. Steve and I took a lap around New England a few years ago on that bike it returned just about 41 MPG for the 750-mile trip. No complaints on that.

A few years ago, on a trip to West Virginai with her bike, she go several tanks over 50 MPG, with a high of 59 on one tank.

Nice to know that it might go up if I shorten the vent hoses.

.

[Slycox]

Well, if your bike is all stock, than something is wrong, it may be;
gas sucked in through the petcock vacuum hose?,
Carbs set too rich?
main jets too big?,
tire pressure low?,
brake shoes dragging?, check the calipers maybe one needs overhaul,
Slipping clutch?, replace discs and springs

What would be the best way to check of gas is being sucked in through the petcock vacuum hose?

Haven't noticed the brakes dragging but will double check.
Tire pressure is ok.

I haven't touched the clutch but if this continues after I pull the carbs and double check them then I will start working that end of things.

Thanks for the info

[Slycox]

Ok so I just got back from a longer highway ride this year, most of my riding has been in town this year. It was pretty windy out. When I left it was in between 15-20mph winds in town. Pretty sure I was fighting almost 30mph winds the whole time. But I topped off before I left and when I got back. I got almost 34mpg, I tried to keep the bike above the 4k line the whole time. Could this be part of my issue is the slower in town pace?

[tkent02]

Other things to check, cam timing, clogged exhaust, ignition timing if you have not checked it yet, bad chain/sprockets, spark plugs, carburetor synch. Wheel bearings, tires, brakes, all of the usual suspects that add a little drag can have some effect. Sometimes it is a combination of a lot of different things just a little bit off, it's like each is multiplied by the next until the fuel consumption really sucks.

[RedBaron]

I know my newer triumph even struggles quite a bit on lower speed stuff in town. On long trips it gets 50-55ish but drops significantly on fun roads or in town. I don't know how my GS does really as it's either through town or full tilt and not much in between so it sucks down some fuel. I know I fill up twice as often on the GS and I think it has a larger tank (and the Sprint doesn't go too far on a tank).If the air cleaner were restricted it could cause a rich condition but I do not know specifically how that would translate into fuel economy, but I'd assume it'd be for the worse. In 12 years I don't think I've ever had a bike come in with a fuel economy complaint so I'd be lying if I claimed to know exactly what needed to be done. If your engine is capable of good efficiency power wise I'd assume it would translate over to economy. In that case I'd wonder about compression, proper jetting, air cleaner cleanliness, and spark efficiency given you've already went through what you've went through. I suppose how efficiently it rolled would play a big factor too. Both shaft drive GS I've had weren't exactly without drag, but I know pushing around the shop the tire pressure that works for me on twisties doesn't roll as well inside for me. Guessing I'd say i'm in the mid to low 30s on fuel economy with my GS but the fun roads here are pretty tight and I don't treat it kindly.

[Slycox]

Many thanks folks, I guess I've been kinda focused on the fuel delivery system in my thinking for this, I will start looking into the mentioned things to check.

[JJ]

Check if the carb vent tubes are are routed incorrectly. They should end above the float bowls.

I have never seen a factory GS with the vent hoses ending above the float bowls. I have owned four, all in stock configuration, and the vent hoses all ended well below the carbs.

[Buffalo Bill]

What would be the best way to check of gas is being sucked in through the petcock vacuum hose?

Haven't noticed the brakes dragging but will double check.
Tire pressure is ok.

I haven't touched the clutch but if this continues after I pull the carbs and double check them then I will start working that end of things.

Thanks for the info

You can buy a hand vacuum pump, useful for some things. Test it with that or…
You can just suck on the petcock hose, and if you get gas in your mouth, the diaphragm needs replacing.
If you can't get a rebuild kit for the petcock, you'll have to replace the whole unit.
All these things I've serviced in my GS1100G, or other bikes.
Most recently I had the clutch slipping in my 1100G, so replaced the discs and springs. I calculated it was losing about 10% of power and RPM.
The first problem I had was the petcock diaphragm, I just replaced the whole unit, but on later bikes I found petcock rebuilding kits that saved me some money.