Vent pipe/Breather?

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tizdaz

tizdaz

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Hi guys, ok so ive done a mod to my fuel tank to help with the leaking, seems to be working but im a little curious.. The valve ive fit is one way, when i blow into it, nothing, but if i suck, then it opens up (ok that sounds wrong on so many levels! but you know what i mean hopefully!)

So my question is... I was under the impression that the tank needs to vent? Pressure builds up in tank & it needs to escape, ie: vent pipe? or gas cap if stock?

But my vent cap works opposite direction, it wont let any air out, but it lets air in!? is this correct :o ?

The mod ive done is similar to this: https://www.ebay.co.uk/itm/333355420134 & i sealed the small breather hole in the gas cap.

Any ideas? As on my last outing, my engine stalled a couple of times & its been a nightmare to start! but this may have been a tuning issue?
 
so is this how the gas cap vent works also (except for the letting fuel out bit!) ..i always thought the gas cap released build up of pressure!?
 
So the correct thing that needs to happen is that air needs to be introduced into the tank to displace the diminishing liquid so the liquidcan move freely which is why it vents in. When the tank is completely empty of liquid fuel it technically isn't empty, the cavity is full of air at atmospheric pressure.. only time pressure within the tank is an absolute issue is when the engine is not running. And if the engine is running the diminished fuel will cause a slight vacuum which is how the air is entering.
 
Rep732 said:
So the correct thing that needs to happen is that air needs to be introduced into the tank to displace the diminishing liquid so the liquidcan move freely which is why it vents in. When the tank is completely empty of liquid fuel it technically isn't empty, the cavity is full of air at atmospheric pressure.. only time pressure within the tank is an absolute issue is when the engine is not running. And if the engine is running the diminished fuel will cause a slight vacuum which is how the air is entering.
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cool make sense now, thanks ;)
 
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