I currently in running my GS500F on Prime I am getting vacuum to the petcock but the bike will  die out if I run it on the on position I guess it needs a rebuilt diaphragm or something anyways if I run it on Prime will that use up all the reserve gas or will it stall when it reaches the reserve level

Prime and Reserve use the same inlet inside the tank. So, yes, running the bike on PRI will eventually run you completely out of gas.

Try taking apart (carefully) the frame petcock and cleaning everything. Especially make sure that the part of the diaphragm that holds the Oring and the hole it enters is really clean. Do not stretch the spring. Cleaning out worked pretty well on my GS500f--now I only have to use prime if I go over a real 75mph or so for a few miles.

Quote from: ajensen on July 17, 2017, 04:32:34 PM
Try taking apart (carefully) the frame petcock and cleaning everything. Especially make sure that the part of the diaphragm that holds the Oring and the hole it enters is really clean. Do not stretch the spring. Cleaning out worked pretty well on my GS500f--now I only have to use prime if I go over a real 75mph or so for a few miles.

Does going over 75mph give you fuel starvation issues? I've never had that problem.

No I have no fuel starvation issue I can do 90 no problem all day

My problem is when I run the frame petcock on on it stalls after the gas runs out of the gas line so I have to run it on Prime but I think if I put it on reserve it runs okay which really doesn't make sense doesn't

Make sure your gas lines are not too long, and like someone else suggested take the petcock out and clean it up.

Quote from: Gcook57 on July 18, 2017, 06:27:17 AM
No I have no fuel starvation issue I can do 90 no problem all day

Quote from: Gcook57 on July 18, 2017, 06:28:15 AM
My problem is when I run the frame petcock on on it stalls after the gas runs out of the gas line so I have to run it on Prime but I think if I put it on reserve it runs okay which really doesn't make sense doesn't

Sorry, I was asking ajensen about the fuel starvation above 75 thing.

As for your issue, I would first double and triple check that all of your fuel lines are intact and/or not clogged. Sometimes they can appear fine on the outside but be swollen shut on the inside. Once you've verified the fuel lines are good, if you still have issues, either rebuild or replace the frame petcock.

Yes--when I bought my GS500f in February, the petcock did not work on regular or reserve, so I had to use prime all the time. I found that there was no vacuum to the petcock, so I eliminated all the vacuum lines I could. Then there was vacuum to the petcock. I then pulled the petcock out and cleaned it. I did stretch the spring a little, which, when I think of it, was stupid. I just wanted to make sure the petcock would close tightly. Now, everything works fine except at high speeds after awhile. I believe that because the vacuum is lower at those speeds, the petcock valve closes enough to shut off the fuel. The more I open the throttle, the lower the vacuum, compounding the problem. However, it does not bother me because I rarely ride at sustained high speeds--most of my riding is back and forth in town or out in the Tennessee/North Carolina/North Georgia mountains, where I have to shut the throttle off, which causes the vacuum to rise again. I had thought about buying a mechanical petcock, but I really like the feature of the vacuum petcock

Quote from: ajensen on July 18, 2017, 10:00:47 AM
Yes--when I bought my GS500f in February, the petcock did not work on regular or reserve, so I had to use prime all the time. I found that there was no vacuum to the petcock, so I eliminated all the vacuum lines I could. Then there was vacuum to the petcock. I then pulled the petcock out and cleaned it. I did stretch the spring a little, which, when I think of it, was stupid. I just wanted to make sure the petcock would close tightly. Now, everything works fine except at high speeds after awhile. I believe that because the vacuum is lower at those speeds, the petcock valve closes enough to shut off the fuel. The more I open the throttle, the lower the vacuum, compounding the problem. However, it does not bother me because I rarely ride at sustained high speeds--most of my riding is back and forth in town or out in the Tennessee/North Carolina/North Georgia mountains, where I have to shut the throttle off, which causes the vacuum to rise again. I had thought about buying a mechanical petcock, but I really like the feature of the vacuum petcock

If I were you, I would simply replace the OEM frame petcock

When I bought the GS, the deal was that I would sell my 1978 Yamaha SR500 to pay for the Suzy (my wife takes care of the money in the house--I just make it). I have not found a buyer for the SR, so I cannot spend any more money. I guess that is a good excuse, but I really like to tinker with things, so I always try to fix things myself without spending any money. You are right--a new OEM petcock would fix the problem.

Quote from: ajensen on July 18, 2017, 10:32:17 AM
When I bought the GS, the deal was that I would sell my 1978 Yamaha SR500 to pay for the Suzy. I have not found a buyer for the SR, so I cannot spend any more money.

Where are you located?  I like the SRs, I wouldn't say no to owning one.  I could maybe find the money, depending on what you're asking.

Cleveland, TN--close to Chattanooga.

I'm like 90% sure I have the same issue, and need a new petcock.

One thought though. I'm running it ON, and the gas runs out after 10-15 minutes because vacuum isn't letting the main line fill up fast enough,  then I switch to prime and everything is fine. But using the Prime function will drain your reserve line, which can leave you stranded if youre not careful. However, after a bit of driving on prime, the main line has gas in it again because its able to fill up again slowly. Could you, theoretically, then use the ON function as your emergency reserve line?

I know leaving it on Prime while not in use is a little risky, in case your floats get stuck, because then it'll pour out into other places. Really I need to replace the petcock I think. But for the time being, I think thats an OK solution?

Quote from: Shift-E on July 19, 2017, 04:10:43 AM
I'm like 90% sure I have the same issue, and need a new petcock.

One thought though. I'm running it ON, and the gas runs out after 10-15 minutes because vacuum isn't letting the main line fill up fast enough,  then I switch to prime and everything is fine. But using the Prime function will drain your reserve line, which can leave you stranded if youre not careful. However, after a bit of driving on prime, the main line has gas in it again because its able to fill up again slowly. Could you, theoretically, then use the ON function as your emergency reserve line?

I know leaving it on Prime while not in use is a little risky, in case your floats get stuck, because then it'll pour out into other places. Really I need to replace the petcock I think. But for the time being, I think thats an OK solution?

I think you've misunderstood how the different petcock positions actually function. The different petcock positions don't actually draw fuel form different sources, they simply switch which inlet inside the tank is being used. The inlet for ON is higher up than the one for RES/PRI so when it stops taking in fuel, you can switch to RES and use the remaining fuel in the tank. PRI is the same as RES except that it bypasses the vacuum aspect of the petcock. So, no you couldn't use ON as your reserve, because if you've used all the fuel in the tank by riding while on RES or PRI, switching the petcock to ON won't supply you with fuel. I suppose there will technically be a tiny amount of fuel left in the actual fuel line itself, but that wont be enough to actually get you anywhere.

I think you should replace the petcock if you've determined that it is the source of the problem, but until you do, run the bike on RES rather than on PRI, to prevent fuel overflow in the case of stuck floats.

Quote from: qcbaker on July 19, 2017, 05:41:06 AM
I suppose there will technically be a tiny amount of fuel left in the actual fuel line itself, but that wont be enough to actually get you anywhere.

This is what I was thinking, just using the bit of gas thats in the line. I know they draw from the same fuel source, but my understanding was that when you switch to RES after your tank has run dry, you're relying on only the gas that's actually in the RES fuel line (not a separate tank) and is enough to maybe get you to a nearby gas station just a couple of clicks away. I was wondering if theoretically you could treat the main fuel line the same way, after the RES line dries out and relying on the little bit of gas in the main line to me out of where I get stranded. But i see what you're saying about it being higher and not functioning well as a reserve. The vacuum aspect probably wouldn't let it be an efficient reserve.

Quote from: qcbaker on July 19, 2017, 05:41:06 AM
I think you should replace the petcock if you've determined that it is the source of the problem, but until you do, run the bike on RES rather than on PRI, to prevent fuel overflow in the case of stuck floats.

This is good to know. I didn't know if RES bypassed the vacuum like PRI does. I will make sure to set it to RES as a safety back up.

Quote from: Shift-E on July 19, 2017, 05:52:27 AM
This is what I was thinking, just using the bit of gas thats in the line. I know they draw from the same fuel source, but my understanding was that when you switch to RES after your tank has run dry, you're relying on only the gas that's actually in the RES fuel line (not a separate tank) and is enough to maybe get you to a nearby gas station just a couple of clicks away.

Not exactly. When you switch to RES you're not relying on just the fuel that's in the lines, you're relying on the fuel that remains in the tank. I think it's a bit over 1 US Gallon, but I'm not 100% sure on that, someone else can probably supply more accurate specs lol. Anyway, the ON position draws fuel in from a tube that protrudes upward into the tank. Any fuel that is below the top of this tube is your "reserve." Switching to RES or PRI uses an inlet at the actual bottom of the tank.

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I was wondering if theoretically you could treat the main fuel line the same way, after the RES line dries out and relying on the little bit of gas in the main line to me out of where I get stranded. But i see what you're saying about it being higher and not functioning well as a reserve. The vacuum aspect probably wouldn't let it be an efficient reserve.

I don't know that the vacuum aspect has much to do with it. It's simply that the tiny amount of fuel left in the actual fuel line is unlikely to get you more than a minute or two of riding. Not really enough to get you to a gas station unless the gas station is already walking distance away... The actual reserve should get you much further (50-60 miles).

Quote from: qcbaker on July 19, 2017, 09:54:32 AM
Anyway, the ON position draws fuel in from a tube that protrudes upward into the tank. Any fuel that is below the top of this tube is your "reserve." Switching to RES or PRI uses an inlet at the actual bottom of the tank.

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OHHHHHHHHHH this makes waaaaaaaay more sense lol. This is my first bike and I've only had it for a few months haha. Ive never seen the other end of the fuel chicken, so i didn't know

I learned something new today.