Hissing sound coming from bike after being ridden for a while and turned off

[Silent21]

Hello Everyone,

I'm a new FJ owner, and I was wondering if anyone know what the hissing sound was that I hear every time I turn the engine off after a ride.  The sound is similar to air escaping a pinched balloon.  I can't figure out where its coming from.  I thought it was from pressure that had built up in the gas tank but after opening the gas cap the sound still persists.  It lasts for a while and eventually quits. 

Thanks,

Silent21

[carsick]

That was the ego of those other riders with you. Deflating.

[FJmonkey]

Silent21, your bike is singing to you from the gas cap. The cap has flapper valves to allow pressure to equalizes as pressure changes from consumption, temperature, etc... It's a SMOG thing for many models to prevent gas fumes from venting to the atmosphere. The sound is harmless to humans but might bother dogs and bats (depending on the bat and the sound frequency). Some FJ owners have had problems with vacuum lock on non-fuel pump years (Tell us what year yours is). If you have problems like running out of fuel on a tank with fuel in it (tank bags make this problem worse for some), then you may need to perform a "Flapper Ectemy". Before performing any procedure consult one of the many write-ups on how not to lose that tiny (Very tiny) ball bearing hidden in your gas cap. In the future when asking for help, please include the year and any modifications (if known) for the poor sods that want to help. Congratulations on your FJ ownership, Moditis is just around the corner....

[FJmonkey]

That was the ego of those other riders with you. Deflating.

Less technical but I love your answer. Can I change my post now? I really meant that the sound was caused by what CARSICK said...

[racerman_27410]

you dont really have to worry any about the singing...... its when the singing stops that the trouble starts.


KOokaloo!


Frank

[Mark Olson]

uhhh guys , he said the gas cap was open and he still had a noise.

I say check for a boiling battery.  the fj is know to overcharge and cook a battery.

[FJmonkey]

uhhh guys , he said the gas cap was open and he still had a noise.

I say check for a boiling battery.  the fj is know to overcharge and cook a battery.

Good point, it was not clear if he put the cap back on after opening. If the singing stops with the cap open and returns with the cap back on then its the flappers. If the singing (Pinched balloon sound) is present with the cap open then it cannot be gas cap, check the battery.

[Silent21]

Thanks everyone for the good answers.      My bike is a 1990 with 2800 miles, no mods as far as I can tell.  I will check to make sure my battery is not getting fried. 

Thanks

[Mark Olson]

Thanks everyone for the good answers.      My bike is a 1990 with 2800 miles, no mods as far as I can tell.  I will check to make sure my battery is not getting fried. 

Thanks

Is that a misprint on the mileage?  a 90  with 2,800 miles would be a great find.

[craigo]

Thanks everyone for the good answers.      My bike is a 1990 with 2800 miles, no mods as far as I can tell.  I will check to make sure my battery is not getting fried. 

Thanks

Is that a misprint on the mileage?  a 90  with 2,800 miles would be a great find.

Hey, even with just 28,000 is still a great find.  Judging from the pic in the avatar, it is in prestine condition

[Silent21]

That's not a typo.  Its only got 2800 miles.  its a cream puff, it was in perfect condition until it was dropped tr day before I bought it. It has some minor scratches but other than that its gorgeous.  Not a bad find for my first bike.  I rode it to work today I will check the battery this ending and let you guys know if that's the problem.  I'm thinking is nothing.

[Travis398]

That battery vent hose should be checked, if pinched off it could definitely hold some pressure, keep you from charging properly, and even boil the battery. 

[Silent21]

I checked and the sound is definitely not the battery.  I believe that its just the pressure being vented.  Thanks everyone for your help and suggestions.