Gas tank belching

[Bill Lloyd]

I had this problem last year, once, with my '81 GS850G; now all of a sudden I had it at my mechanic's shop, with my "new" '82 GS1100G, and he said he's never seen anything like it. I'd filled the gas tank shortly before getting there [but not quite up to the bottom of the "neck"]. As we were working on the bike, gas started streaming out from under the filler cap. Took off filler cap, cleaned up, jiggled bike, a few burbles of air [I presume] came up, and the gas level went back down. Then it rose again. This scene was played out four times in a row. All the mechanic could think of was that perhaps somehow air was getting sucked up into the tank through the carbs???? Can this have something to do with the vacuum valve? Anyone?

Thanks.

Bill Lloyd

[retrex]

Two guesses

First, there should be a tiny hole in the neck near the top. If is rusted shut or blocked in some other way then when engine heat or sun warms the gas suficiently it will produce enought vapor pressure to force the gas up through the cap. Normally this only happens when the gas is at the level, or above, the bottom of the neck. The tiny hole is supposed to let the pressure bleed out through the gas cap. Second, you also may have too good a seal with your cap which will not allow built up gas pressure to vent. BTW this used to happen to me on my cross country jaunts when I used to fill the tank as much as possible to extend running time. Good luck.

[Bill Lloyd]

Gas tank belching

Thanks!

- Bill

[Clone]

Take a center punch and make that hole at the top of the fillerneck bigger. That should take care of your problem.