Fuel reserve.

[Rhyseeroo]

Hello, I am still a newbie rider, so this may be an obvious question, but I was riding home from work and Mt bike started sputtering and losing power, I figured I might just be low on gas, so I pulled over to the shoulder and it finally stalled on me. I get off and open the gas tank to see if I have any gas left, and although it's a visibly small amount, there is gas left in the tank. So I figure I would try to switch the petcock from being pointed all the way down to pointing all the way up. It was still having trouble revving up. Well after a bit it started to rev just fine, so I carried on and filled it up with gas and it seemed fine for the remaining 3 miles home after that. My question is, how does the petcock/ fuel reserve work? There's 3 places I can switch it to, "On", "Pri" and "Res" is the fuel reserve a separate section that holds the gas, or does it hold the gas in the main tank, it just needs to be switched when the tank is very low? Also what do the 3 settings on the petcock mean/ in what situations do you switch to each.

Thanks in advance! And thanks for answering my super dumb questions!!

[mr72]

ON -> normal
RES -> as you figured out, this is reserve
PRI -> for priming the carb, like after you have removed it or the carb is empty of fuel for whatever reason. This bypasses the vacuum diaphragm that usually switches the gas on and off when on RES or ON

RES and ON are normally connected to different length intake tubes inside the tank, so the higher tube feeding "ON" will be above the fuel level when it gets to about 1 gallon left, and then you can switch to RES and it has a lower pickup point and will utilize most of that last gallon of gas. The purpose of this is, as you figured out, since there is no fuel gauge, to give you warning you are going to run out of gas while still allowing you to continue to a gas station.

Don't leave it on PRI while parked. It will likely flood the carbs and may even leak gas all over the ground and fill the crankcase with gas in the process. You can leave it on RES or ON while parked, the vacuum petcock will close and prevent fuel flow while the engine is not running.

You did it right. Ran out of main fuel, switched to RES, then got more gas. Switch back to ON, otherwise next time you run out you won't have reserve to bail you out. Most of us old folks use the trip odometer as a fuel gauge, and learn from riding about how many miles you can go before you need to fill up without running into the RES-ON dance. On my GS with the larger late-model tank, I get about 150 miles before getting close to hitting RES, which is about 50 mpg for 3 gallons. YMMV. Literally.

[The Buddha]

There's 2 levels in the fuel pickup in the tank. So reserve isn't a separate tank. Its the lower 2-3" of the tank. However there's also ~1/2 gal you can never get out because that is even lower than the pickup.
Cool.
Buddha.

[Bluesmudge]

Those 2 guys pretty much answered everything, but I'll add one more bit of info. You said, "although it's a visibly small amount, there is gas left in the tank." The GS500 tank has a very large and flat bottom and short sides. So even a small amount of gasoline will look like a lot. It's almost impossible to gauge how much fuel you have in the tank by looking at it. 1 gallon and 3 gallons look very similar.

Best to just fill it up, ride till you hit reserve (bike will start sputtering, reach down and turn the petcock before the bike dies), and then start looking for a gas station. Always reset the trip meter with each fill-up. That is your fuel gauge. You fill find you always hit reserve around the same mileage +/- ~10 miles.

[HPP8140]

Echo all the good points above...when you gain more experience you will reach down and turn to reserve when you feel the engine hesitating. I've gained the bravery to know I can usually safely go 40 miles on my 02 GS after hitting reserve or reallllllllllllly push 50  don't try this at home kids

[Rhyseeroo]

Everyone here is so helpful, thanks yall!!