What's causing a popping sound from tank/petcock?

The bike is a 83 1100 Ltd shaft model. Whenever the gas gets down to about 1/3 in the tank, the tank starts making a popping sound when idoling, roughly at the rate of 4 to 5 betas per second. It sounds like the tank is being hit lightly with a hard object from inside. That bike has been making this sound as long as I've owned it (7 years), but I just finished rebuilding the motor and cleaned the carb so I had a wishful thinking that the noise would go away.

If I touch the petcock I can feel the beat. I also see the gas flow in the fuel line pulsating at the same rate. I have never seen (heard) this in the half dozen bikes I've owned although none were as large as 1100. Does anyone experience this? Is there a fix?

SO! your the one thats got him!!!!

you got that Travelocity Gnome in your tank and he is sending Morse code trying to get someones attention to let him out.

you need to to cut a big hole in your tank and let the little guy get out.

If you dont, we will report you to the SPCG, That's the Society for the prevention of Cruelty to Gnomes.:S

Sorry, just came to me. have never heard of a problem like yours. pretty strange.

If fuel tank cap is opened, does same sound continue?

Thinking cap vent might be clogged.

Good Luck!

Is the bike equipped with a fuel gauge?

dman3998 wrote:

SO! your the one thats got him!!!!

you got that Travelocity Gnome in your tank and he is sending Morse code trying to get someones attention to let him out.

LOL. Wish it was the gnome; I could simply feed it to my iguana. No wait, he's strictly a vegetarian I forgot!

Patton wrote:

Is the bike equipped with a fuel gauge?

It is. It's working fine.

As for the sound when the tank cap is open, I'll have to check that later. Where's the cap vent? Is that the large rubber ring beneath the cap?

I just want to ask everyone this: do you feel pulsation when you touch your petcock (I have a mild fear that this sentence is taken to mean something else...)

It could be the petcock itself. If the spring is weak or if there is a small vacuum leak or if you don't hold your mouth just right, the petcock diaphragm can falp back and forth with the rhythm of the vacuum pulse from the carb. A plugged tank ventcould also contribute to the music.

TexasKZ wrote:

It could be the petcock itself. If the spring is weak or if there is a small vacuum leak or if you don't hold your mouth just right, the petcock diaphragm can falp back and forth with the rhythm of the vacuum pulse from the carb. A plugged tank ventcould also contribute to the music.

Since two of your mentioned the possibility of clogged vent, can you please point me to the exact place where I should check? A replacement tank cap doesn't cost much, but I'd be happier if I can fix it.

I rebuilt the petcock last year (I think), and I assume the rebuild kit came with a new spring.

First, test by running with cap open or ajar, and if problem persists it's likely not vent related. If noise stops, then time to clear the vent.

As to fuel gauge, was thinking maybe some part on sending unit was possibly bonking against inside of tank.

Good Luck!

4 rolls of duct tape, Take the tank off the bike and make sure it is at the gas level you hear the beating. Now tape that drum..er tank right to the top of the washing machine. Now drop a nice big wet bath towel on one side of the tub. Set it on spin and there ya go. Whatever is in there will either exit the bung at ludicrous speed or be pulverized into silence.

I'm betting on the gas level float.....

Patton wrote:

First, test by running with cap open or ajar, and if problem persists it's likely not vent related. If noise stops, then time to clear the vent.

As to fuel gauge, was thinking maybe some part on sending unit was possibly bonking against inside of tank.

Good Luck!

I just filled up the tank this morning, so I'll do the test when the level gets lower. Thanks for the explanation.