See the pix here when I was having an issue with vacuum forming in my LIKE's tank ---big sucking noise when I opened the cap.
Cap is supposed to let air vent in - but mine wasn't.
For gas to leak out onto the ground it seems to me it must have pushed up the filler neck AND pushed out of the cap to reach the rubber cup thing around the cap - which collects over filled gas and empties it down the hose to the ground. So, if you over fill at the pump, the gas will not go into the engine area - but drain down the hose onto the ground under the scoot.
That tiny vent hole (see photo) leads into the fumes collecting EPA/Tree-hugging octopus of hoses & charcoal cannister via a little black thing that looks like a fuel filter but is actually a one-way valve. I do not see how gas could get to the ground via that hole or that hose system...? It had to push clear out of the cap to that over-flow boat and then drain to the earth.
BTW: if your cap 'sucks' when you open it - try blowing into it with a can of PC air and/or removing all the hoses and that 1-way valve and blowing/draining them. I did all the above and the cap stopped holding a vacuum and began venting as my dealer mechanic told me it should. I have no clue why it was fixed and venting properly - just another testimony to my mechanical abilities.
The top arrow is pointing to the over-flow hose connected to the over-fill boat.
Sure, and don't overfill.
Who knew?
Stig
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