Tank venting?

[rosso75]

I have 3 FJ's.  One is a '90, stuck in eternal project status.  One is an '86 that I bought about 9 months ago.  It was running, barely, and was taken apart in an attempt to find the problem.  The third is also an '86.  I got it a month or so ago, and it runs, so I'm using it to diagnose the problems with #2 by swapping parts from #3.  So far all I've done is verify that a lot of parts are good, but there's still stuff left to check.

Anyway, I had both tanks off of the two 86's and noticed an occasional hissing/squealing sound from one of them.  The tanks were sitting in the sun, so I assumed that pressure was venting off as the tank heated up.  Then I realized only one of the tanks was doing it, and it further occurred to me that my '90 never did that.

So I'm wondering what kind of venting system there is on these tanks.  Is the one making the noise venting properly, and the one not making the noise  is maybe plugged up?  Or is the one not making the noise venting properly, and the one that's making noise is doing so because it's plugged up?

Is there something I need to clean or replace while I've got these tanks off?

Thanks a bunch

[andyb]

Flappers are what's making the noise.  Pull the cap apart (carefully, many tiny bits that will jump into the tank or elsewhere) and remove the orange things.

And/or search "flapperectomy" on this very site.

[aviationfred]

I have an 89' and occasionally I hear a high pitch whistle coming from my fuel cap. There have been a few threads on here that have mentioned this. My understanding is that the whistling is a good thing, and the tank is venting pressure properly.

For the 86' models, I have seen references to a flapectomy performed on the fuel cap.

Fred

[rosso75]

You guys rock.  Thank you

[movenon]

Gas Cap Info.

http://www.fjowners.com/index.php?topic=2024.0

George

[rosso75]

Pull the cap apart... and remove the orange things.

With the intention of cleaning them, or just removing them from the assembly entirely?  One of those unnecessary things, like an appendix? 

Thanks

[FJmonkey]

If you pull just the orange thingies out, make sure you put the white thingy back the same way it came out. It can be put in upside down. DAHIK 

Your tank will no longer vent, yep, vapor lock. I say just pull the white thingy with the orange thingies out as one piece and reassemble....

[theLeopard]

yo, I've got a '92 and I my tank whistles when it's hot.
i'm new here but my guess is if the pressure wasn't venting at all your tank would explode on long, hot routes from the pressure like a 200kph pipebomb.

[movenon]

yo, I've got a '92 and I my tank whistles when it's hot.
i'm new here but my guess is if the pressure wasn't venting at all your tank would explode on long, hot routes from the pressure like a 200kph pipebomb.

I think it is sucking in air not venting it out. Air has to replace the fuel you are using. 
George

[FJmonkey]

I think it is sucking in air not venting it out. Air has to replace the fuel you are using. 
George

Yep, the whistle is air being sucked in, the flapper valves prevent the air (with gas vapors) going out...

[ribbert]

I think it is sucking in air not venting it out. Air has to replace the fuel you are using.  
George

Yep, the whistle is air being sucked in, the flapper valves prevent the air (with gas vapors) going out...

I'll put a foot in both camps and say it does both  

Consumed fuel needs to be replaced with air, as mentioned above, sucking air in.

Fuel tanks build enormous pressure when hot, where does that get released?

Leave a container of fuel out in the sun on a hot day and it will bulge on all sides and when your undo the lid there is a rush of air that sometimes even knocks the lid from you hand, but you never get that rush of escaping pressure when you open the FJ fuel cap under the same circumstances.
Engine heat alone will make your tank almost too hot to touch, that's a lot of pressure.

You have consumed fuel that needs to be replaced and you have pressure from expanding, heated vapour that needs to be expelled. Each of these require air travelling in different directions at different times. The cycle, duration and circumstances under which each occurs will be all over the shop and depends on all sorts of constantly changing criteria and is not even worth speculating on, suffice to say, it is required to do both, suck and blow.(IMO)

Noel

[MatYl]

I agree with Noel.
Two flapper valves, one for incoming air and one for outgoing: in my FJ flappers were on both sides of white plastic thing and one let air in and other air out.

[ribbert]

I have observed many times that fuel only starts to leak after the bike has been parked a while or even overnight. I suspect (never devoted much thought to it) this is tied in with improper tank venting.
Anyone care to offer an opinion?

Noel

[FJscott]

I have observed many times that fuel only starts to leak after the bike has been parked a while or even overnight. I suspect (never devoted much thought to it) this is tied in with improper tank venting.
Anyone care to offer an opinion?

Noel

Noel, is this a rhetorical question? Somehow I feel this is a trap.

Scott

[ribbert]

I have observed many times that fuel only starts to leak after the bike has been parked a while or even overnight. I suspect (never devoted much thought to it) this is tied in with improper tank venting.
Anyone care to offer an opinion?

Noel

Noel, is this a rhetorical question? Somehow I feel this is a trap.

Scott

Ha ha ha. whatta you guys think of me?

Scott, this was literally a passing thought I had on the odd occasion the bike started leaking fuel, either many hours after it had been parked after a ride or at times, the following morning (or sometime through the night)

I never bothered, and still haven't, to think through the effects of temperature changes and contraction and where and what this could contribute to the event so long after without touching the bike.

Something had physically changed because it wasn't leaking and then it was. I speculated that the only thing that changed over that time was temperature, ambient, motor, fuel etc.
I stopped thinking at that point (yes, have your fun if you must) and was just reminded by this discussion.

I thought some might enjoy the process of thinking through what effect the contracting pressure in the tank would have if not vented properly.
Nothing sinister about it, I'm not waiting to pounce.

Noel