Gas tank odd sound.

[Tony M]

This weekend I had my first ride. What a great feeling to be back in the sandal again after a long winter and not so great spring weather wise. When I got back home and turned the bike off I heard a strange sound coming from the gas tank. I opened the cap and heard what sounded like a tap running. I could also see gas moving around (near full tank). Again all his is happening with the bike off. I turned on the key, heard the fuel pump activation and started the bike. I turned it back off and let it sit. I was considering removing one battery but decided to get the service manual. Shortly after, 10mins the sound stopped. I do remember during the end of my ride I was smelling some gas. For my bike that is a normal occurrence during hot summer days riding in traffic and bike gets hot. I figure that is the byproduct of a hot engine heating up the gas tank. But it wasn’t that hot and the bike did not feel that hot. Engine thermostat was normal. Just wondering if I should be concerned. Any thoughts?

 

[Larry Fine]

Sounds like typical tank burping through the cap.

 

[cjames431]

Normal. Mine does it too.

 

[SMSW]

Sounds like typical tank burping through the cap.

He heard the noise with the cap off - which should relieve all pressure and noise. I think this is atypical - maybe caused by a damaged or flooded charcoal canister? The only time I experienced anything like that was during a rest stop on a OHSTOC ride. It was a very hot day and I'd been riding hard (a fast group) to keep up, doing a lot of shifting and accelerating. (Aside here...I know I could have been smoother, keeping my speed up in curves and not needing to accelerate between sweepers, but I'm not comfortable at high speeds in curves where I cannot see the whole road ahead and oncoming traffic). When I stopped, I the heat rising off the bike was palpable, and the gas was boiling(?). I heard the noise and popped the cap - sure sounded like boiling gas.

 

[jfheath]

I have observed this as well. Plenty of fuel in the top tank - enough to see the fuel level. The surface was disturbed and it appeared to be caused by bubbles, which I assumed were coming from the lower tank.

The smell of petrol was coming from on of the rubber tubes that emerge below the bottom of the rear of the crankcase behind the large footpeg bracket near to the gear lever. This was fuel vapour - I could see the light shimmer / disturbance caused by the emerging fumes. Like a heat haze.

This has only happened when the engine is very hot and I've only ever noticed it on very hot days.

There is going to be considerable disturbance of fuel between the two tanks - hotter fuel will rise, colder fuel will sink, and without any fast air movement the temperature difference between the upper and lower tanks will change.

Any fuel next to the tank sides, closest to the engine / exhaust may turn into vapour, like you see in a pan of water as soon as you put it on the stove. Movement upwards through the surrounding fuel will cool most if them down again.

To boil, all of the fuel needs to be doing this, which isn't going to happen. But the behaviour is normal.

What is more alarming is the ST1300 ghostly cry - like opening your mouth and making a sound while breathing in. It happens at night when you go into the garage alone, hours after a long ride. The bike has cooled but there is still that really pleasant smell of warm bike, oil and fuel and that alone may be the reason for your nocturnal visit. I'm sure that it is addictive

You've just settled in to carrying out a few aimless tasks - to justify popping in for a 'fix'. So you're probably moving things around from where you last put them, to somewhere else where you won't be able to find them (like their proper place). Whatever it is, you are engrossed and quite happy with the fact that you are alone in there in the middle if the night.

Then without warning, there is this deep, hollow, ghostly, 'last gasp' moan which instantly raises the hackles on the back of your neck

What the .....

 

[Upt' North]

I think they call it character. My 11 was always farting at me.
The MOT tester swore there was something wrong with the vent, every year when he took the cap off it hissed at him like a Cobra.
And if you think the tank of a 13 gets hot take a ride on a K1100...

 

[Sadlsor]

Then without warning, there is this deep, hollow, ghostly, 'last gasp' moan which instantly raises the hackles on the back of your neck

And they say the ST has no soul.
Ha!

 

[Oldbikefixr]

I think they call it character. My 11 was always farting at me.
The MOT tester swore there was something wrong with the vent, every year when he took the cap off it hissed at him like a Cobra.
And if you think the tank of a 13 gets hot take a ride on a K1100...

Had the same with our 1991. I rode it home, about an hour trip and did a walk around to check for leaks and obvious issues. The tank was grumbling and when I removed the gas cap, it made a very pronounced sucking noise. Started back up fine and we rode it around for a few weeks and I continued my list of things to fix. Tank was still sucking but no apparent problem. When I did the fixes on my list, I replaced the cap and vent hoses. No more tank noises regardless of ride length or temp conditions. Kind'a miss it.

 

[Sadlsor]

Hmm.
First I've seen, of anyone replacing the gas cap.
Except for those who installed a twist-off to eliminate the key action.

 

[SMSW]

Hmm.
First I've seen, of anyone replacing the gas cap.
Except for those who installed a twist-off to eliminate the key action.

I installed an Oberon twist off and had no noises whatsoever from my gas tank after that. I did have some teething problems with the O-ring. I replaced the damaged one with the wrong material O-ring and it did not like gasahol. Once I got that squared away and bought the correct ring, it lasted for a couple of years.

 

[woodybelle]

Mine makes these noises also, the hotter the engine the more the noise. I see bubbles in the tank when the noise happens.

 

[core-aggie]

I had a similar issue with the gurgling.

I found the problem "by accident".

Consider the hose that feeds fuel from the upper tank to the lower tank. As I was swiveling the upper tank back into place, I noticed that transfer hose "crimp" as the upper tank sat in its final position.

Turns out the previous owner obviously had a hose failure and bought a "generic" hose to fix it.

That factory hose is custom molded with curves and the inlet end and outlet end are different ID's. A generic straight hose ain't gonna work

 

[Andrew Shadow]

...... the inlet end and outlet end are different ID's.

Depends on the model year.
On 2007 and earlier, different diameter. 2008 and later has a uniform diameter.

 

[Mellow]

Depends on the model year.
On 2007 and earlier, different diameter. 2008 and later has a uniform diameter.

Article [13] - ST1300 - Lower Fuel Tank Hose - pre-2008 vs 2008+ | ST1300 Articles

I'm copying this post to a new thread in the ST1300 FAQ section of the Articles to make it a little easier to find. It's also in this thread: https://www.st-owners.com/forums/showthread.php?115913-ST1300-Fuel-Tank-Hose-Leak-(Near-Miss) Okay, here goes. Now, after you look at all the pictures...

www.st-owners.com

 

[Tony M]

Thanks to everyone who replied to this post. Love this forum. Yesterday took the bike out for another ride. No burping. I also confirmed the fans on the rad work fine. You don't know how relived I am that Estees and I are aging together. We both now have a burping problem.