This is wierd and embarassing.  I have  a GS500F.  I'm not sure about its fuel capacity but I think that main is about four gallons, reserve about one gallon.  My petcock has three settings, "on", "res", and "pri".  This is what I THOUGHT that they meant:

"on"= main tank only
"reserve"=reserve tank only
"prime"=inject fuel into carbs, if needed

Each time I fill the gas tank, I fill it right to the brim and reset the trip odemeter.  I get 55mpg and I refill at 200 miles.  This afternoon I was at 191 miles before starting the bike.  I decided to switch to reserve before starting my trip, just to be safe.  

I looked down and was surprised to see it ALREADY on reserve.   I thought "Gee, how could I have driven it for months on reserve? The reserve is only a gallon.  I should be running out every 55 miles."

Then I did something really stupid.  I decided that I must not understand what reserve means.  So I switched it to "ON".  I got about ten miles before the bike stopped running.  

Then I did something else stupid.  I decided that the bike must be out of gas.  So I went and got a gallon of gas.  When I started to fill the tank, I was shocked to see gas already in the tank.  There was about a gallon in the tank, BEFORE I started to refill it.

After emptying my one-gallon gas can into the tank, I switched it to prime and started it. It ran perfectly.  I switched to reserve and it continued to run fine.

Clearly there is something that I just don't get about petcocks.

http://www.gstwins.com/forum/viewtopic.php?p=145199#145199

http://www.gstwins.com/forum/viewtopic.php?p=145312#145312

The ON setting will run all of the gas in the tank except for the reserve pocket.  The Res setting will run all of the gas in the tank including the reserve pocket.  If you're careful about filling by the odometer, you can run on Res all of the time.  ON/Res is just there to give you warning of when you're low.
Pri runs fuel to the carbs without a vacuum.

You might have the 'direction' the valve is pointing backwards, in which case you had it on Pri and not ON, and you flooded the engine.  Possibly.  Read manual, young man.

I guess that's a search ding and a manual ding.

Are you sure the lines haven't been reversed at some point?

edit: RG beat me to it, but I'm nicer.  

Yep, I'm a Mean Person.  

:lol:

Yeah, I now realize that I misunderstood what "reserve" means.  I thought that the reserve was a totally separate fuel supply.  But that was wrong. On "reserve" you can use BOTH the regular and reserve supplies. That is why I was able to drive around for months at that setting.  And actually, that is where I should keep it, because I am using the trip odometer.

Quote from: OhioSteveYeah, I now realize that I misunderstood what "reserve" means.  I thought that the reserve was a totally separate fuel supply.  But that was wrong. On "reserve" you can use BOTH the regular and reserve supplies. That is why I was able to drive around for months at that setting.  And actually, that is where I should keep it, because I am using the trip odometer.

Just realize if you run on Res, when you run out of gas you completely run out of gas...and now you're pushing.  Why not run it on "On" and switch when it coughs?  At least that way you have some indication that you're getting low.  It's trivial to flip the petcock from the seat without slowing down.