Ok, a bit over 12,000 miles, mostly city driving, I got 55+ mpg when I got my 93 GS 2yrs ago, riding like I did not know what I was doing (mainly because I still don't  ).

Now it is down to around 35 mpg, basically riding like I stole it. 

New plugs, oil change w/filter, air filter, brakes and tires two wks ago.

Starts fine, sounds fine, rides fine.

Comments or suggestions? (Yes I have my asbestos underwear on. )

Jim

Check your plugs.. you running rich? Check under the bike, you leaking gas?

new plugs, no leaks.

consider me an idiot, how do I check for running rich?

by pulling the plugs, and seeing what color they are.

AHHH someone else is having MPG problems like me, except I've been getting 25MPG. Same symptoms (basically no symptoms).

How do these look?

Edit: I looked at the threads more than the head of the plug.. they look ok-ish to me, but I'm an idiot, wait for a guru to chime in..

Black = rich, white/grey = lean

Plugs should be an even tan/light brown color (I don't have any pics to show, sorry)

Did you do ANYTHING to your carbs at all?

also edit: here's a picture from google

I did nothing to the carbs at all.

ya know, those plugs don't look new to me, I think the guy that "changed" em didn't. 

Wondering about the oil and filter now also. 

I think those plugs look pretty good. I'd recomend checking your float height and make sure you don't have any leaks. Do a valve clearance check too. When was the last time that was done? Dirty and worn chain and sprockets could have an effect too, as well as low tire pressure.

Gunning your GS good will return low mileage, like all engines. Try riding around at some legal speeds in top gear. Take a trip and then fill up and calculate your mileage, if it returns ok then you have no problem. Around 45 should be ok i think for modded bike.

ok, I'll try riding smoother for a good distance. btw no performance mods to bike.

unknown when last valve check done, chain & sprocket clean, tires at 33f 35r.

Make sure your chocke isn't stuck partially oper too. Try disconnecting the cable for a while and see if that makes a difference.

Hmm yes, +1 on unadjusted/stuck choke. That would explain bad mileage.

Do the valve adjustment.  It might help some and if you don't know when the last time it was done, then it is time.  I agree with checking the stuck choke.  But, that would make your plugs look super rich.  The choke blocks air flow and therefore richens the mixture.  Your plugs look ok to me, but if you have a stock bike they normally look lean on the GS.  So for your plugs to be the right color something doens't seem right.  Which leads back to the choke and valves.  Those are the only things I can think of.  Just basic tune up type stuff. 

Just a point of information, I'm fairly certain the choke on our bikes is an enrichener, and it's its own circuit which adds more fuel, instead of a traditional choke, which chokes off airflow. But yeah, that would make your plugs show really rich..

There's definitely something wrong with that mileage.  My GS is modded / jetted and I ride around like I'm high on crack all the time and get close to 50 mpg. 

But yeah, your plugs look fine and dandy, so I doubt you're running rich in anyway.  If you were, especially with a stuck choke, you'd start to have serious running issues as those plugs fouled up, and that doesn't seem to be the case here.

Do the basic tune up stuff: clean the chain, check valve clearances, check/replace the plugs, clean the air filter, check tire pressure, check float height, etc.  I would also check all the hoses under the tank, make sure none of them look damaged.  Maybe also try running a can of Seafoam in the fuel, oil, and through the intake.

Gotta agree there I WOT from light to light in town and still get about 40-45 mpg.  When I act right and am out on an open road its in the 50's.   Seafoam is magic though, I've got a buddy that has an 84 honda POS car with like 350,000 miles on it all he does is keep the oil fresh and add a can of seafoam to his gas every other tank....