Bikes: MTS12S, R1, off road stuff, and vintage stuff too.
Posts: 828
Join Date: Aug 2002
Mood: MTS1200 - yum yum yum yum yum yum yum ...
sounds very odd. My st4s has never done this, but will regularly leave a puddle from the vent if I overfill it. I'd be checking the pair of filler vents. There is one which vents from around the outside of the filler neck. The other one vents from the top of the tank. Its unlikely this has dropped off else you would get fuel all over the place even when the tank wasn't full as the pressure builds up inside it (ask me how I know <roll eyes>).
The best way to check all the internal tank pipes is to remove the fuel pump & sender unit out of the bottom of the tank. You obviously need to drain it to do this. Unbolting the filler and lock won't show you anything.
Make sure the moving part of the filler cap is nice and tight when its shut. You may need to swap washers around under the lock part to get it to close up a bit tighter. Leaks from the cap tend to be more obvious when the bike is on the side stand.
The tank vents through a hole in the filler cap which leads to another hole over the rubber grommet at the back of the filler aperture. Check for muck/gunge below the rubber grommet. If this gets blocked pressure in the tank might force petrol up through the filler lock mechanism.
Hybrid Mode
