Gas tank overflows

[Tom1276]

My brother's 82 GS1100G has a tank that was resealed with an unknown compound prior to his purchase three years ago. He states that when he refuels the tank he leaves one to two inches below the fill hole. In the time it takes to go into the gas station to pay for gas and get back there is gas flowing out from around the gas cap. He states that when he blows on what he believes to be the overflow tube he hears bubbles coming from the fuel level indicator on the bottom of the tank. It has me baffled. Any ideas?

[posplayr]

gas expands as it heats up. I have ridden to the gas sation to fill up. come back 3 miles. Everything cool but a little later gs is overflowing as it warms and expands

[FlyingSteve]

Little problem with your theory about the gas expanding is that when you fill up, the gas comes out at a cool 55F... So, no... It won't get hot enough to expand and over-flow in the amount of time it takes to go into gas station and pay for the gas and come back out.

And besides, as the gas heats up, it evaporates more rapidly (not expand, as in like water expands as it freezes). So, you shouldn't have gas billowing out of the tank for any reason.

[Nessism]

Not sure if it's expansion or what have you but overflowing gas after filling up too high is common. There is a small hole in the filler neck which allows the expanding gas somewhere to go, and that hole is often plugged when people coat the inside of their tank. Make sure that hole is open and don't fill up so high and you shouldn't have the issue.

[posplayr]

Little problem with your theory about the gas expanding is that when you fill up, the gas comes out at a cool 55F... So, no... It won't get hot enough to expand and over-flow in the amount of time it takes to go into gas station and pay for the gas and come back out.

And besides, as the gas heats up, it evaporates more rapidly (not expand, as in like water expands as it freezes). So, you shouldn't have gas billowing out of the tank for any reason.

Unfortunately it is not theory, lifted my clear coat near the filler cap after sitting in the garage 24 hours.

[posplayr]

Not sure if it's expansion or what have you but overflowing gas after filling up too high is common. There is a small hole in the filler neck which allows the expanding gas somewhere to go, and that hole is often plugged when people coat the inside of their tank. Make sure that hole is open and don't fill up so high and you shouldn't have the issue.

When you say small hole are you talking 0.025" or smaller? I just looked and I saw nothing although there was a small spec that looked like it was almost a weld.

[FlyingSteve]

Not sure if it's expansion or what have you but overflowing gas after filling up too high is common. There is a small hole in the filler neck which allows the expanding gas somewhere to go, and that hole is often plugged when people coat the inside of their tank. Make sure that hole is open and don't fill up so high and you shouldn't have the issue.

If the breather hole is plugged up, then yes, pressure will build and you will get liquid gas out.

A buddy of mine has a new Ninja 250 and when we hang out in his garage you will hear the bike whistle every like 10min. It is from gas evaporating in the tank and when the pressure builds high enough the little breather valve opens and releases the pressure. It's pretty funny if you aren't aware of it and all of a sudden the bike, not running, just makes this like heavy sigh noise lol.

[Tom1276]

When you say small hole are you talking 0.025" or smaller? I just looked and I saw nothing although there was a small spec that looked like it was almost a weld.

This info would be very helpful as the hole is not obvious when we looked for it. He has an extra tank that has no gas in it (nor fumes) that he can manipulate while looking. It would be helpful if we knew a size and approximate location.

He insists that he can fill the tank to within 2inches of the bottom of the fill hole and watch it rise with the gas cap off while sitting on the bike. He can shake the gas level down even BEFORE it gets to the bottom of the metal of the fill hole. Seems to be defying laws of physics... I am baffled. Is it possible that fuel lines are crossed somewhere? Maybe the material used for lining the inside of the tank has air pockets?

[tkent02]

The hole is about 1 mm in diameter, about 15mm or so down the right side of the foller neck on most GSes.
If it is clogged, the expansion of air in the rest of the tank forces fuel up into the filler neck, and out all over the tank.

The air in the tank will heat up and expand very quickly if the sun is hitting the tank.

Knock that sealer out of the hole, it does not hurt to make the hole a lot larger, too.

[posplayr]

The hole is about 1 mm in diameter, about 15mm or so down the right side of the foller neck on most GSes.
If it is clogged, the expansion of air in the rest of the tank forces fuel up into the filler neck, and out all over the tank.

The air in the tank will heat up and expand very quickly if the sun is hitting the tank.

Knock that sealer out of the hole, it does not hurt to make the hole a lot larger, too.

Thanks I found and un plugged it.

That little know tidd bit would have saved me a paint job

[rich]

The hole is about 1 mm in diameter, about 15mm or so down the right side of the foller neck on most GSes.
If it is clogged, the expansion of air in the rest of the tank forces fuel up into the filler neck, and out all over the tank.

The air in the tank will heat up and expand very quickly if the sun is hitting the tank.

Knock that sealer out of the hole, it does not hurt to make the hole a lot larger, too.

This is Rich; my brother started this thread for me and my bike. Thanks for your input, found the hole it was plugged, opened it up will drill it out bigger in the very near future. I think this will solve the problem with this tank.