Air escaping from my gas tank?

Question

I had to remove my gas tank to get painted. I left the gas in it and just turned the k**b to off. So I put it back on and whenever I run the bike and shut it off, I hear this whistling sound. It seems to be air creaping out from around the gas cap. When I open the cap, it sounds like a can of soda being opened. I'm not sure if air is creaping in or out but it's whistling.

What is causing this, and will it harm the bike?

It's a 94 ZX-6. I don't notice and performance issues at all and there are no gas / other fluid leaks.

Answer 1

The seat might be pinching the vent hose.

OR the vent tubes might be plugged up, when the tank was painted.

Remove the riders seat and check.

Blow into the hose with the gas cap open - there should be no restriction.

Remove the hose from the tank, reinstall the seat, go for a ride, then open the gas cap.

Answer 2

The fuel tank is being pressurized by vapourization of ethanol alcohol added to the fuel. Theoretically it could force fuel past the float needle and flood the carbs.

Answer 3

The gas caps have a built-in vent to release pressure created by the gas sloshing around from heat.  This is to eliminate "vapor lock" that used to be an issue in cars long, long ago.  I don't know if today's fuel additives/blends have an effect on pressure or not but the caps pressure release valve has always been working, even if you never noticed.  Also, I wouldn't think painting the tank would have any effect either.

    There is nothing to worry about.  This sound lets you know the vent is doing its job, keeping the engine running normally.

Answer 4

The "can of soda" sound is air rushing in. When running the engine, gas is being consumed, but not enough air is entering the tank, so you are creating a vacuum.  This would make it harder for the engine to get gas and might "run out of gas" even though you have some - especially if you fill it all the way up (little air) and drive for a long while (no air to expand).

The whistling noise is probably some air getting in, but not as much as before.

My guess is that the paint is covering an air hole?