Tank venting?

[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

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

Noel
I have experienced oil and fuel leaks on old dried up o rings, gaskets and hoses. When they dry up they lose the ability to expand and contract with changing ambient/ engine temps. I've seen o rings turn square. On my FJ the fuel hose from petcock to filter was so hard and brittle it felt like a partially frozen water hose, crunchy.
I feel that with the newer ethanol fuels this process happens quicker, reducing the life span of anything made of rubber or buna-n. When I replaced my fuel filter and hoses I used a marine hose designed for use with ethanol fuel.
So I would guess your hypothesis of changing ambient temps resulting in the leak is on the money.

Scott

[theLeopard]

this is oddly familiar to the problem i'm repairing right now (carb overflow) so my question would have to be "where is the leak?".

that said since it's a relatively-sealed system, and you got me thinking now - this is strictly conjecture, most of the pressure would exist within the tank/pan. it may very well create draw throughout all your fuel/oil lines as well but I sincerely doubt enough pressure would occur to 'bleed' those lines internally.

but then i'd have to ask "where is the leak?" and, when you reply, I only know the answer to one possible scenario.

fun game, noel, I hope I didn't make an ass of myself 

[Pat Conlon]

We all know about knackered needle seat o rings, wrong float settings, leaky non buoyant floats, debris in the needle seat....all causes fuel overflows.

How about syphoning? A interesting fix: http://www.fjowners.com/index.php?topic=7056.0

[simi_ed]

I hope I didn't make an ass of myself 

I think the skipper already cast off the bow line, and is getting ready on the stern line as well ...