I guess I shouldn't say "old"... My bike is a 2007 GS500F.

About a month ago my bike started having issues while I was riding it. With the petcock in the "run" position, the bike would start lurching, and the RPM's would drop no matter what I did to keep them up; until the bike eventually would die on me.

It seemed to idle fine, but it would act up anytime that I rode it somewhere. So, I took it to a friend's house and he helped me clean out the carbs, the gas tank, and the air filter. He checked the spark plugs, put in a new battery, and adjusted the carb mixture screws. We thought that the issue may have just been bad gas (the previous owner neglected the bike), so my friend ran ethanol treatment with some new gas through the bike. He also ran seafoam through it.

The bike ran really well for about a week, but it started acting up again a couple of days ago. I did find a way to help with the issue though, and I think that it may narrow down the problem for you guys.

While riding with the petcock in the "run" position... the bike slowly died on me. I pushed it into a hotel parking lot. I tried to start her up again; no such luck. For some odd reason I decided to try it with the petcock on "pri". She started up fine, and she got me all the way back to my destination without issue.

I tested this discovery by riding down the road on "run", and it would act up. While I was still riding I would switch it to "pri", and the issue would clear up immediately.

Bad fuel line, petcock, evil minions?

Thoughts?

This is a known issue with various different years, but it's possible you have some of that "bad gas" clogged in the petcock. Take it off, disassemble it and make sure all the passages are clean and clear. They are small like the carbs and sticky gas can clog it up. Mine did that for a while as well, until I got it cleaned out and now it works perfectly.

How many miles before it started acted up?  Did you try switching it to reserve?  It might be possible that you are just running out of gas.  It might look like you have plenty of gas, but the flat bottom of the GS tank can fool you.  It's happened to many people here.

Other than that, you might check the vacuum line from the carbs to the petcock.  It sounds like the petcock vacuum system is no operating properly.   When you put it on prime, it bypasses the need for vacuum, and also uses the reserve line.

Quote from: Soloratov on July 05, 2013, 05:40:54 AM
This is a known issue with various different years, but it's possible you have some of that "bad gas" clogged in the petcock. Take it off, disassemble it and make sure all the passages are clean and clear. They are small like the carbs and sticky gas can clog it up. Mine did that for a while as well, until I got it cleaned out and now it works perfectly.

I thought that my friend had cleaned out the petcock, but I will check it again.

Quote from: bombsquad83 on July 05, 2013, 05:41:28 AM
How many miles before it started acted up?  Did you try switching it to reserve?  It might be possible that you are just running out of gas.  It might look like you have plenty of gas, but the flat bottom of the GS tank can fool you.  It's happened to many people here.

Other than that, you might check the vacuum line from the carbs to the petcock.  It sounds like the petcock vacuum system is no operating properly.   When you put it on prime, it bypasses the need for vacuum, and also uses the reserve line.

It started acting up about 100ish miles after my friend and I had it running good again. It has about half a tank of gas... So I'm thinking that's probably not the issue.

Does it hurt the bike to run on prime while I figure this out? I turn the petcock back to "run" when I shut the bike down.

100 miles if you didn't completely fill up the tank could be entirely possible to hit reserve.  Why not try putting some more gas in to see if it fixes it.  At least try putting the petcock on reserve to see if that solves it.   If it does, you either (A) need more fuel, or (B) have a pinched or gummed up main fuel line.

Quote from: bombsquad83 on July 05, 2013, 06:02:44 AM
100 miles if you didn't completely fill up the tank could be entirely possible to hit reserve.  Why not try putting some more gas in to see if it fixes it.  At least try putting the petcock on reserve to see if that solves it.   If it does, you either (A) need more fuel, or (B) have a pinched or gummed up main fuel line.

We put a full tank of gas in it before I hit the road again (after "fixing" it). I can't imagine that I'd be out of gas 100 miles later. Is it better to run it off of reserve than prime?

Both suck fuel from the same spot, so no, won't hurt anything as long as you don't leave it on there for too long without it running.

Quote from: Soloratov on July 05, 2013, 06:47:11 AM
Both suck fuel from the same spot, so no, won't hurt anything as long as you don't leave it on there for too long without it running.

I usually turn it back to "run" whenever I'm coasting into my parking spot, or I turn it to "run" right after I shut down the bike.

Quote from: Xevamir on July 05, 2013, 06:18:32 AM

Quote from: bombsquad83 on July 05, 2013, 06:02:44 AM
100 miles if you didn't completely fill up the tank could be entirely possible to hit reserve.  Why not try putting some more gas in to see if it fixes it.  At least try putting the petcock on reserve to see if that solves it.   If it does, you either (A) need more fuel, or (B) have a pinched or gummed up main fuel line.

We put a full tank of gas in it before I hit the road again (after "fixing" it). I can't imagine that I'd be out of gas 100 miles later. Is it better to run it off of reserve than prime?

Reserve uses the same fuel line as prime, it just shuts off fuel flow when there is no vacuum.  Prime bypasses the need for vacuum.  I wanted you to try running in reserve as a diagnostic.  You wouldn't be the first one that was adament that their bike was not running out of gas only to find out that their problem is that they needed to flip to reserve or add more.

I have the exact same issue as op. im going to change my fuel lines. I feel like the main one is clogged up. ( I will run reserve as a diagnostic before, great tip. ty). I have a spare petcock that I switched with the existing one and that didn't solve anything.

Quote from: bombsquad83 on July 05, 2013, 06:54:22 AM

Quote from: Xevamir on July 05, 2013, 06:18:32 AM

Quote from: bombsquad83 on July 05, 2013, 06:02:44 AM
100 miles if you didn't completely fill up the tank could be entirely possible to hit reserve.  Why not try putting some more gas in to see if it fixes it.  At least try putting the petcock on reserve to see if that solves it.   If it does, you either (A) need more fuel, or (B) have a pinched or gummed up main fuel line.

We put a full tank of gas in it before I hit the road again (after "fixing" it). I can't imagine that I'd be out of gas 100 miles later. Is it better to run it off of reserve than prime?

Reserve uses the same fuel line as prime, it just shuts off fuel flow when there is no vacuum.  Prime bypasses the need for vacuum.  I wanted you to try running in reserve as a diagnostic.  You wouldn't be the first one that was adament that their bike was not running out of gas only to find out that their problem is that they needed to flip to reserve or add more.

How can my bike be running out of gas when it basically has half a tank in there? I'm confused. I feel like I should be getting more than 100 miles out of a tank of gas.   

Quote from: junk301 on July 05, 2013, 07:07:14 AM
I have the exact same issue as op. im going to change my fuel lines. I feel like the main one is clogged up. ( I will run reserve as a diagnostic before, great tip. ty). I have a spare petcock that I switched with the existing one and that didn't solve anything.

I'm going to try running it on reserve today. I guess we'll see what happens.

Many many many things dictate how many miles you get a tank, riding, air filter, toe if riding (city highway) and reserve sometimes looks like you have a lot left. I would try ruining in reserve, get more gas then at least try to run it on on. Other than that, you could have just got a bunch more gunk in your carbs and pet chicken if you didn't run with an inline filter as well. Key weird COULD. There are many mixed feelings on inline filters lol.

If you fill the gas tank all the way to the top, basically until the gas touches the filler neck all the way around the bottom of it, then you have around 3 gallons of gas before you hit reserve.  It's very conceiveable with a combination of lower than average fuel economy (due to a variety of factors as mentioned), and filling to less than full that you could just be hitting reserve at 100ish miles.  I hit reserve typically around 130 miles on my older '93 that gets around 46 mpg with a 15 tooth sprocket and 125/40/1 washer jetting.  As mentioned before as well, what looks like "half a tank" is not really half a tank on the GS.  It's deceptive. 

I'm not gaurenteeing that this is your only problem, I'm just saying why would you not eliminate the obvious?

I understand what everyone is saying, but before I started having these issues I wouldn't even worry about getting gas until at lease 150 miles. It's just weirding me out, I suppose.

your tank is definitely not empty. I ran my bike today from prime to reserve this time and it still sputtered to a stop...meaning that its most likely a vacuum dysfunction. Since the reserve and prime uses the same fuel line, it means that nothing is clogged in there. TO the experts on the board, would this indicate a vacuum leak? petcock was cleaned recently. carbs were also cleaned. boots are tight.

cheers and many thanks for any response

When mine displayed the same symptoms as yours it was a vacuum line installed wrong. Switched them to their correct  positions and worked again. Make sure you have your lines are correct and are not getting pinched/kinked when re-installing your tank.

Quote from: Twisted on July 05, 2013, 04:04:41 PM
When mine displayed the same symptoms as yours it was a vacuum line installed wrong. Switched them to their correct  positions and worked again. Make sure you have your lines are correct and are not getting pinched/kinked when re-installing your tank.

thanks for the response twisted. when you had this issue. did your top speed falter in any way?? my bike is having that problem, was wondering if it could be another factor...sorry for hijacking this thread momentarily xevamir.

Sometimes thread-jacking can be helpful! Is there a diagram that shows the correct positions for the vacuum lines?

Main GStwin site:

Bless you, laddy. I know what I'll be doing when I get off of work on Monday.