Long range tank - breather line versus fill line

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Originally Posted by the evil twin

Petty tanks aren't supposed to have a 'breather' direct to atmosphere
That is the job of the Charcoal Canister.

You should have the fill line breather that goes from your tank to the top of the filler so you don't get blowback when filling.
Both the filler and fill breather should be sealed from atmosphere with the cap on.
The tank 'evaporates' to atmosphere via the Charcoal Canister and not a separate line

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Ok cool, thanx mate. I'm pretty confident now, that I can leave the fuel tank system as it is. :)
Kallen was telling me the same thing, but I was still bit paranoid. :D ('cos I dismantled every part of the fuel tank system, including the fill point, to clean them).
Cheers.

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Originally Posted by Throbbinhood

The line I'm talking about is the 'charcoal canister line' in your first pic in this thread.

But yeah everything goes to the dual tank filler thing, from memory they are all interconnected etc. Honestly cant remember 100%, but it's sat in the sun in 40+c weather with full tanks and no issues.

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Yeah, I think it's ok, 'cos you divide any possible issues between two tanks(namely the pressure buildup inside). Charcoal canister is also an emission control thing I reckon,(other than saving some petrol fumes and redirecting it to the intake & venting the tank positive or negative pressure to the atmosphere), so it's a modest saving of fuel.
I bet some of the extra pressure is escaping from the petrol cap as petrol fumes, 'cos that's the only way I can think of, since your charcoal canister vent is blocked off.

Apparently in olden days, petrol fumes just escaped to atmosphere from a petrol cap vent valve(or a simple small hole on it).

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Originally Posted by dom14

Or did you mean the "charcoal canister line"(as it's connected in mine) from the top of the expansion tank?
If that's the case, that means "slow breathing/venting" isn't happening in your tank, and fumes just stay inside the tank.
But, having two tanks still minimizes your chances of any pressure build up accidents. Besides, some pressurized fumes might escape from weak points like fuel cap.
I've been wondering whether the fuel cap is designed to allow that to happen, 'cos if you look at the pictures of the fuel cap above, it doesn't look like a simple fuel cap, but some mechanism appears to be there at the bottom of it.

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The fuel cap will in the case of vacuum for whatever reason will allow air through so your tanks don't get sucked in. They should never vent as that's the job of your charcoal canister

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Originally Posted by lucus30

The fuel cap will in the case of vacuum for whatever reason will allow air through so your tanks don't get sucked in. They should never vent as that's the job of your charcoal canister

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Thanx mate.
Yes, now it's obvious charcoal canister performs few important functions and a vital part of the fuel system.
Apparently, it's an emission control requirement as well.
But, old charcoal canisters aren't likely to function well, and I'm pretty sure there are many out there with charcoal canisters not functioning properly.
I'm not sure mine's working properly either, but I'm gonna let it be. :)