pulsing fuel petcock

[Guest]

Ill start off by saying its an 81 GS1100E and has no running issues, but the other day while riding I noticed that the fuel petcock is clicking. If you put your ear to the tank you can hear it very clearly and the fuel line itself is pulsating. I'm no stranger to the vacuum operated petcock having replaced a ruptured diaphragm in the past but i do not remember it pulsating. My original thought was a bad seal or ruptured diaphragm again so, I have a mightyvac with a vacuum gauge and i put it on a vacuum for 10 mins and the gauge did not drop a tick. I have since then replaced the vacuum line to the #2 carb with no difference in results. Ive been a long time reader of the GS resources but first time member, hopefully someone can shed some light on this.

[mrbill5491]

Ill start off by saying its an 81 GS1100E and has no running issues, but the other day while riding I noticed that the fuel petcock is clicking. If you put your ear to the tank you can hear it very clearly and the fuel line itself is pulsating. I'm no stranger to the vacuum operated petcock having replaced a ruptured diaphragm in the past but i do not remember it pulsating. My original thought was a bad seal or ruptured diaphragm again so, I have a mightyvac with a vacuum gauge and i put it on a vacuum for 10 mins and the gauge did not drop a tick. I have since then replaced the vacuum line to the #2 carb with no difference in results. Ive been a long time reader of the GS resources but first time member, hopefully someone can shed some light on this.

Sounds to me the petcock is just pulsing to the #2 cylinder. If you watch the carb boots to the head they will pulse as well. You can even feel it.

[BassCliff]

Hi,

Yes, the vacuum is caused as the piston draws the air/fuel mixture into the cylinder. It is not a steady state like a vacuum cleaner. How about a "mega-welcome"?

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[rustyspokes]

Thanks for the welcome!!! That makes alot of sense I guess i was looking at it from an automotive point of view where a vacuum port on an intake manifold feeds all the cylinders so you have a lot more of a steady vacuum. Plus i just adjusted the valve so the sound is more defined with no valve train clatter to drown it out. I just thought that even at idle (1100 RPM) that the intake stroke would happen often enough to hold the petcock open rather than pulsate.

[Steve]

Plus i just adjusted the valve so the sound is more defined with no valve train clatter to drown it out.

You had valve train clatter???

That's a first, unless the PO (Previous Owner) was worse than usual. Usually, they ignore the valves completely because it costs too much to have a shop do them. The valves always tighten up, so they will ge quieter, not noisier.

I just thought that even at idle (1100 RPM) that the intake stroke would happen often enough to hold the petcock open rather than pulsate.

There is no check valve mechanism in the line or the petcock. Just a simple diaphragm and a spring, against which the vacuum pulls. When the intake stroke is over, the vacuum is gone, the spring closes the diaphragm.

.