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Hello all. I have a ST 4S. Picked it up last June 2019 with 6500 miles on it! I previously had a 907 i.e. with 25000 miles on it.Here is my sitrep. When travelling with a tank bag, I always get a whiff of petrol fumes when I stop. When I remove the magnetic tank bag to inspect, the bottom of the bag has petrol moisture on it from the spot above the gas cap.
Has anyone else experienced this phenomenon? Is my gas caps' gasket too weathered to seal properly? It visually looks fine....
What do you all think?
Dennis
 

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There is a breather pipe within the tank top, a small rubber grommet. Check it is clear and try some spray in it to see if it vents to the hose which ends at the front bottom of the fairing
 

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You probably did not have the gas cap sealed. Press down on the gas cap with your thumb after closing it and removing the key. You should here a "click", which means the gas cap is actually closed and sealed tight.
 

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This happened on my ST4 when I got it. As part of the used bike tuneup routine, I put a new fuel filter in and when I had the tank open I blew some compressed air into the overflow and evap lines, confirmed they were clear, and sealed it up. It still had the problem afterward, so I bypassed the evap canister and connected the evap and overflow lines with a Y connector as they do on non-USA bikes, and that fixed the problem. Make sure you plug the evap lines going to the canister or throttle bodies (however you decide to do it) if you end up having to bypass it, as it will create an air leak if you don't.
 
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