Gurgling sound in fuel tank

Constant Mesh · Jul 31, 2014

Often after I've shut down my hot FJR I'll hear a significant gurgling sound in the tank after two or three minutes.

I assume some of the gas has transitioned from a liquid to a vapor. Don't know where it's occurring although probably somewhere near the fuel pressure regulator I'd guess.

I believe there's a check valve on the output of the pump so the bubbles probably aren't originating there.

Can someone explain what's happening?

Mihalis fjr · Jul 31, 2014

Pretty normal i believe!I heard the same noise from my 03/abs...

Warpdrv · Jul 31, 2014

Yeah I get that also with my 05.... never bothered me....

one good thing to do with a bike your age if you haven't already is remove gas cap and clean that baby up, do some maintenance - keep the vent lines clear....

Here's a good thread about the gas cap with lots of breakdown pics from Fred W on page 2.....

Gotta say Fred is awesome to have around on the forum here... !!

https://www.fjrforum.com/forum//index.php/topic/18042-gas-cap-modification/page-2

ionbeam · Jul 31, 2014

Mihalis fjr said:
Pretty normal i believe!I heard the same noise from my 03/abs...

Yes, the sound is normal, what he is asking is what is causing the noise.

Depending on octane and additives gas can boil between 100º and 400º and boiling can be triggered by a nucleation point so the noise might be boiling gas. There is also the possibility that the noise is air bubbling through the gas. The early Gen I bikes would rarely but significantly accompany the gurgling with a geyser of fuel out the filler when the cap was opened. I'm old enough to remember when vapor lock which was caused by vaporized fuel was a problem for carbureted engines.

The OP rides in a hotter part of the country and heat almost always seems to be an element of the gurgling. Does the gurgling noise happen only when the gas volume is low? Does it happen only when the bike and ambient are very hot? Does it happen when running fuel from one brand of gas (additives may affect the occurrence).

I don't *know* what the noise is but I sure suspect what the noise is.

RossKean · Jul 31, 2014

It sounds that there may be a problem with the fuel filler cap not venting properly. I think FredW did a write-up on servicing this.

Edit: I'm slow on the keyboard today!

Warpdrv · Jul 31, 2014

I'm pretty sure IonBeam hit it with the heat of the fuel under the tank bringing it to a boil..... mine does that more noticeably on hotter days also....

Bugnatr · Jul 31, 2014

Thanks Alan, I've had the boiling numerous time on my KLR when working the bike hard in hot weather.

It's a good idea to slowly blow some compressed air through the vent line next to the filler tube. Years ago FJRob had his line plug and the fuel tank actually imploded and the tank had to be replaced.

WBill · Jul 31, 2014

The gas used to get so hot in my '05 that it would shoot out of the tank when cool fresh fuel hit it. I cured the problem years ago by installing a heat shield under the tank. WBill

Constant Mesh · Jul 31, 2014

Not suggesting it's a problem. It's just something I've noticed on many occasions. Probably during the hottest times of the year.

Has nothing to do with the tank venting system. When the bike sits outside very long with the sun heating the tank and contents I'll often notice a wet spot on the ground just beneath the vent hose. Obviously it's venting gas fumes which condense back to a liquid on their way down and out the hose.

I don't know if the level in the tank has an effect.

I wonder if the Gen II's do it? I'd guess not since they don't have a fuel return line from the fuel rail like the Gen I's.

dcarver · Jul 31, 2014

can be triggered by a nucleation point

When the nucleation point generates neutrons, does the mpg increase?

ionbeam · Jul 31, 2014

dcarver said:
When the nucleation point generates neutrons, does the mpg increase?

Youse fissile 233 guys, everything seems to fall apart when you discuss generation. This non radiation nucleation is about flashing over a fluid to a vapor, and even better than cold fusion, this can actually happen in your very own gas tank. I'm sure that this is exactly the kind of thing that beemerdon talks about while ~~swigging~~ sipping Hornitos Reposado Tequila with his buds. Then they too gurgle.

RadioHowie · Jul 31, 2014

ionbeam said:
dcarver said:

When the nucleation point generates neutrons, does the mpg increase?

Click to expand...

Youse fissile 233 guys, everything seems to fall apart when you discuss generation. This non radiation nucleation is about flashing over a fluid to a vapor, and even better than cold fusion, this can actually happen in your very own gas tank. I'm sure that this is exactly the kind of thing that beemerdon talks about while ~~swigging~~ sipping Hornitos Reposado Tequila with his buds. Then they too gurgle.

Alan, you have absolutely transformed into what I call a "Wordsmith" the past few days, particularly with your VMax tip-over story. I ROFL'd!

wheatonFJR · Jul 31, 2014

Alan has always been that way. You've just been too drunk/stoned/stupid to notice it before.

RadioHowie · Jul 31, 2014

Thanks for the vote of confidence, but I maintain his posts of the past couple of days have been "gold", and not just in the technical "gold" we're all so familiar with.

wheatonFJR · Aug 1, 2014

Howie, we all are confident in your abilities...

Alan, usually throws in three or four layers of hidden meanings in every third post. I laugh out loud at some of them at my desk. Coworkers turn heads...

Fred W · Aug 1, 2014

Constant Mesh said:
Has nothing to do with the tank venting system.

I would disagree.

Since I castrated my tank in the previously mentioned thread, I have never since had the tank gurgles, though I had experienced them prior.

I suspect that the gurgles have more to do with the buildup (and subsequent release) of vapor pressures in the fuel tank, than the actual boiling of the gasoline liquid.

While the BP of gasoline does range as low as 100 to 400F, and so it is technically possible to boil the gasoline if the fluid reached over 100 and you had a ****** volatile load of fuel, the observed fact that the symptom goes away entirely when the pressure restraint mechanism is removed kind of kills that idea.

wheatonFJR · Aug 1, 2014

I don't know Fred...PV=nRT

Bounce · Aug 1, 2014

At the very least service the vent if you don't want to castrate it.

https://www.fjr-tips.org/maint/ff/ff.html

RadioHowie · Aug 1, 2014

wheatonFJR said:
I don't know Fred...PV=nRT

I dunno...I'm more particular to

Gurgling sound in fuel tank

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