Low fuel problem

[Darthbrugg]

So I have been lurking for the past few months and finally summoned enough courage to ask the pros here. Let me give you a little background first:

Bought my GS a few months ago from a guy at work and have been riding it everyday. In the last few weeks I have noticed that if there is about 1 gallon of gas left in the tank I get typical fuel starvation problems. This occurs at low and high speed riding with the petcock on PRI. Once I fill it up everything runs fine. The PO had the carbs cleaned along with some parts replaced about a year ago. The shop also replaced the entire petcock assembly on both the frame and tank.

My main question is what would cause the bike to stutter and eventually cut off at low speed with the petcock set to PRI?
Thanks

[steezin_and_wheezin]

this sounds similar to when i first got my bike

Check out this Wiki Page:

PRI = Prime(not PRImary)
ON = Standard setting for Main tank
RES = Reserve Fuel

you should be running on "ON" position for normal riding.

i may be mistaken but, if you run on PRI setting you will be actually pulling from the RES fuel outlet. so the hesitation/stutter you're feeling is probably the bike about to run out of gas

[Darthbrugg]

I originally ran it in the ON position until I experienced the fuel starvation problem and after reading in to the problem switched it to PRI. 

[GSnoober]

So I have been lurking for the past few months and finally summoned enough courage to ask the pros here. Let me give you a little background first:

Bought my GS a few months ago from a guy at work and have been riding it everyday. In the last few weeks I have noticed that if there is about 1 gallon of gas left in the tank I get typical fuel starvation problems. This occurs at low and high speed riding with the petcock on PRI. Once I fill it up everything runs fine. The PO had the carbs cleaned along with some parts replaced about a year ago. The shop also replaced the entire petcock assembly on both the frame and tank.

My main question is what would cause the bike to stutter and eventually cut off at low speed with the petcock set to PRI?
Thanks

That last gallon of gas is most likely to be diluted with a fair amount of water, which is why you're having these problems. Normal condensation inside the tank fills the bottom of the tank with water; water is heavier than gasoline, so the remaining gas floats on top of the water. When the level of fluid (fuel and water) gets low, you switch the petcock to RESERVE or PRIME, and that is when you start drawing the diluted fuel into the carbs.

Of course, this is why GS5 tanks rot at the bottom; the "crap pockets" fill with water because they are the lowest points of the tank. Search the term "crap pockets" if you're not familiar with this issue...

You can add a few ounces of plain rubbing alcohol to help overcome this; the alcohol will mix with the water and make it more likely to burn in the combustion chamber. However, it would be MUCH better if you drain every drop of fluid out of the gas tank and refill it with fresh gas.

Several years ago, I demonstrated this very problem for a dis-believing friend. I drained the last gallon of gas out of a GS500 tank and poured it into a gallon jug. Within just a few minutes, the gas and water had separated; the water was at the bottom, with the gas floating on top. You can't completely stop the condensation from forming inside the tank, but you can help to prevent it by keeping your tank full. No air in the top of the tank means no room for the water vapor to condense and run to the bottom of the tank...

Drain your gas tank into a clear container and watch the fuel float to the top; after you've done that, refill the tank with fresh gas. Trust me, the crap pockets will thank you...

[ben2go]

The reserve and prime passages in the frame petcock are smaller and more restrictive than the on setting.Please note that the last half to one gallon of fuel will not flow out of the tank petcock because of the tank and petcock designs.It's this way on all GS.If the frame petcock has a torn internal diaphragm,it will cause similar running issues.I despise the stock frame petcock design and upgrade them.You should also take a few minutes to clean the fuel cap internals to make sure it's venting properly.

My write ups.
http://gstwins.com/gsboard/index.php?topic=56352.0
http://gstwins.com/gsboard/index.php?topic=41061.0

[Darthbrugg]

Thanks for the suggestions guys. Definitely going to clean the gas cap this weekend when I clean/ lube the chain.

I have been looking into replacing the petcock but I'm kinda confused on the different choices. If I did just the frame replace using Ben's write up, there would still be a tank petcock correct? Also looked at doing the Pingle petcock but didn't know if that removes the frame petcock.

[ben2go]

Thanks for the suggestions guys. Definitely going to clean the gas cap this weekend when I clean/ lube the chain.

I have been looking into replacing the petcock but I'm kinda confused on the different choices. If I did just the frame replace using Ben's write up, there would still be a tank petcock correct? Also looked at doing the Pingle petcock but didn't know if that removes the frame petcock.

The GS has two petcocks.The frame mounter one that you replaced,and the tank mounted one.There's rarely a problem with the tank petcock.Leaks are common and a dirty strainer is common.You can remove and clean the tank petcock without any real issues,well except for removing the tank.If you change the stock petcock you loose the reserve function on the frame petcock.The tank petcock get's fuel from two levels,and then feeds it to the frame petcock so you have on and reserve.I feel a write up coming on.I'll do a tank petcock cleaning how to write up in the next few days.Weather permitting.