Losing vacuum when gas tank is low

[Guest]

Took a ride from Milwaukee to Chicago and back on Sunday, and about 1 mile from my friend's house it died suddenly. It felt like the engine just stopped getting fuel and puttered out as I slowed down for a stoplight. I was just a block from the nearest gas station so I pushed it over there and called my friend. I thought initially I must have run out of gas, but when I opened the gas cap and gave the bike a wiggle I could still see gas at just about the level the fuel sending unit is at. Put it on RES, still nothing. Put it back to ON and added some gas to about half way full. Still would not start. Friend arrived and we started going though the basics. Saw that fuel would start to flow into the carbs but then stop, as if there wasn't even vacuum to keep a continuous flow going. Saw an air pocket or two. I thought of how a pool pump works and how it loses it suction when the water level is too low in the pool or if an air pocket is in the line. So, we decided to put the petcock on PRI for about 10 seconds and saw fuel start to go all the way down into the carbs. Switched the petcock back to ON and boom - she started right up and ran normally as she did before.

I replaced the petcock with an OEM one earlier this year. Never had issues before. The only difference is that this was the first time gas was ever low in the tank. I've kept it pretty full since I started riding this season.

I did a search and found this thread:

http://www.thegsresources.com/_forum/showthread.php?209584-82-GS850GL-Fuel-issue&highlight=low+fuel+tank+dies

Could that petcock filter be gunked up already? I've put less than 200 miles on the bike since it was replaced.

Maybe my gas cap? Although when I took it off and put it back on it made no difference - still wasn't getting fuel to the carbs.

For now I'll be keeping the tank full, but I'd like to prevent this from happening again.

[rudeman]

Why did you replace the old petcock?

[tom203]

Your pool pump air pocket analogy is pretty good. You were running in "on" petcock spot and gas level dropped below pickup and engine died - too late to switch to "res" spot as no engine vacuum to get fuel flowing. You need "pr" spot in this instance.

[growler]

It was stuck in the ON position, couldn't rotate it and I got a deal on a new one.

Why did you replace the old petcock?

[rudeman]

Do you have a vent line on your tank? It's a rubber hose that runs from underneath the fuel tank. If you do and haven't yet, I'd check it to make sure it is clear and not pinched.

[Agemax]

Do you have a vent line on your tank? It's a rubber hose that runs from underneath the fuel tank. If you do and haven't yet, I'd check it to make sure it is clear and not pinched.

that would be a drain for the fuel gauge sender unit, NOT a vent line

[Steve]

Do you have a vent line on your tank? It's a rubber hose that runs from underneath the fuel tank. If you do and haven't yet, I'd check it to make sure it is clear and not pinched.

I have worked on MANY GSes over the years and have never seen such a "vent" tube.

However, on bikes that have a fuel gauge, there IS a tube in that location, but it is not a vent tube, it is the safety drain for the funnel around the fuel sending unit that will catch any leaks and direct them away from the top of the engine.

Still a good idea to make sure it is not kinked or clogged, but it's NOT a vent tube.

.

[Agemax]

I have worked on MANY GSes over the years and have never seen such a "vent" tube.

However, on bikes that have a fuel gauge, there IS a tube in that location, but it is not a vent tube, it is the safety drain for the funnel around the fuel sending unit that will catch any leaks and direct them away from the top of the engine.

Still a good idea to make sure it is not kinked or clogged, but it's NOT a vent tube.

.

wow.......... this thread has an echo!

[rudeman]

The horse is dead...

My mistake, carry on.

[Wingsconsin]

This is more a question to the community rather than a message of solution to Growler ...

IF the petcock is clogged up with interior gas tank debris such that it cannot supply fuel at the REServe level than what would one do about this problem?
To me it suggests that the fuel tank has a lot of "stuff" (technical term) floating around inside and would benefit from a good cleaning?? (There is the question) -

If the answers point to this being a good idea - what would be the method of doing so for Growler to attempt a modification?

If it were me -- I would remove the tank (after getting it as empty as I could) and fill it with some liquid that is cheap, like Seafoam, and not prone to do harm to the innards of the tank and swish it around and dump it as I try to rinse the gunk (technical term also) out..?

SO - Community at large - Good Idea ? or Bad Idea?

[mrbill5491]

Doesn't hurt too clean the tank out now and then. When I do I usually take the petcock off and plug the holes with a rubber cork. Swish away pull the plugs and drain it. Watch it as it drains to see if any solid chunks come out. If some do, might need a bit more swishing. Make sure the gas cap is venting good as well. If it doesn't vent, that will cause fuel starvation as well.

[growler]

How do I know if my gas cap isn't venting properly?

Doesn't hurt too clean the tank out now and then. When I do I usually take the petcock off and plug the holes with a rubber cork. Swish away pull the plugs and drain it. Watch it as it drains to see if any solid chunks come out. If some do, might need a bit more swishing. Make sure the gas cap is venting good as well. If it doesn't vent, that will cause fuel starvation as well.

[growler]

I've run Seafoam through it twice since I got the bike last year. Tank LOOKS pretty clean, but I don't know for sure unless I properly clean it. Hmm. Another late fall project.

This is more a question to the community rather than a message of solution to Growler ...

IF the petcock is clogged up with interior gas tank debris such that it cannot supply fuel at the REServe level than what would one do about this problem?
To me it suggests that the fuel tank has a lot of "stuff" (technical term) floating around inside and would benefit from a good cleaning?? (There is the question) -

If the answers point to this being a good idea - what would be the method of doing so for Growler to attempt a modification?

If it were me -- I would remove the tank (after getting it as empty as I could) and fill it with some liquid that is cheap, like Seafoam, and not prone to do harm to the innards of the tank and swish it around and dump it as I try to rinse the gunk (technical term also) out..?

SO - Community at large - Good Idea ? or Bad Idea?

[81GS850]

I just went through this with my GS850. Take all the components out of the tank and seal it with duct tape or something else. Clean it with phosphoric acid available at Lowes or Home depot. This stuff is used for cleaning concrete and it will only attack rust and not good metal. Rinse with water and either add something to soak up the extra water or dry it and coat it with a tank sealer or in my case, run it as it is with an inline filter. I would also take your petcock apart and blow it out, blowing from the outlet to the inlet. This gets all the junk away from the outlet.

[Chris G]

How do I know if my gas cap isn't venting properly?

I would have though if your tank was not venting correctly after running off nearly a full tank when you removed the filler you would hear any vacuum it had created, had this on an old rover car, a Sherpa diesel van that managed its best to implode the tank, it looked like it has been smacked around with a hammer when it eventually stopped running.