funny fuel leak ST2
 

Just got back from spain with my multistrada and an st2, awesome week's riding however couldn't help noticing that when the ST was filled with fuel and then left for a few minutes it seemed to be venting fuel through the filler cap lock!!

I am guessing that a breather must be blocked somewhere, has anyone else ever had this problem??

was it overfilled, the petrol expanded in the heat of the tank and overflowed? or the tank shrinking from cold petrol?

possibly a combination of both, just seems odd, didn't happen on my 748 last year or the multi

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.

Thanks guys, will get the tank off when we get a chance and have a look what is going on, either that or not brim the tank on a hot day!

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.

My ST2 has never leaked form the filler, but i am aware that when filling, the fuel level must never be above an inch or two below the internal neck. If not, fuel is deposited on the road via an overflow pipe below the belly pan.
I seem to remember reading somewhere that this is normal, but it is a right pain as you never know exactly how full you can get away with, and of course you can never brim it for maximum range.

Regards,
Mike Chadwick

i found if you fill up when the bike is on the side stand and you dont overfill it doesnt leak out of the vent.

thanks guys, guess overfilling may be the issue here.....