Px200: fuel leak

I have a 1998 px200e with approx 20,000Km on the clock.
I have recently experienced a minor fuel leak. When the petrol switch is OFF, and the petrol tank full, the overflow pipe from the carbie drips fuel - only minor amounts, but it does drip fuel.

I thought I had cured this problem by replacing the fibre/sealing washer and hose clamp on the connection/pipe (respectively) feeding into the float bowl.
I also cleaned the fuel filter and sealing gasket ontop of the float bowl and everything was fine.
And now suddenly the problem is back since I filled the tank.

The problem currently only seems evident with a full tank of fuel. But it is there even when the fuel tap is switched off, so it must be part of the carbie which is already filled with fuel leaking - but why would a full tank make a difference? And what part of the carbie is prone to leaking?

Scoot runs really well (though may take 4 kicks to start on a cold morning), starts first kick when warm - but its an annoying problem, mainly coz its intermittent.

Any ideas guys?
[:drink:]

Original von hellcoopz: [?[] Maybe the fuel cap vent (?) is blocked - pressure build up due to full tank not being able to escape thru vent and thus finding another way to relieve itself. Maybe also blocked vent on carbie causing same problem - with fuel tap off there would still be residual fuel in the line and it would be a case of "a little going a long way" ... aircraft hydraulic fluid is like that - one drip looks like litres when it is spread all around the place.

Thanks for the reply - I will investigate your suggestions - I think the fuel cap vent is OK coz this was working fine recently - I topped the tank right up, then the sun came out, the scoot got hot, and there was fuel pissing out of the filler cap vent! But I`ll double check and have a closer look at the carbie too. Cheers.

[?[] Maybe the fuel cap vent (?) is blocked - pressure build up due to full tank not being able to escape thru vent and thus finding another way to relieve itself. Maybe also blocked vent on carbie causing same problem - with fuel tap off there would still be residual fuel in the line and it would be a case of „a little going a long way“ … aircraft hydraulic fluid is like that - one drip looks like litres when it is spread all around the place.

The reason why it only leaks with a full tank is because, I think youll find that fuel is going down the breather tube that normally sticks out above the fuel. If you look in the tank you will see it. Its the one that has a bend in it. When the tank is this full turning the fuel tap off has no effect as it doesn`t shut off this breather pipe.

Having said that fuel shouldn`t really leak out of the carb anyway. It is more than likely that the rubber tip of float needle is worn. Usually this stops flow to the float bowl when it is full but if the needle is worn the fuel will continue to flow in. These are really easy to replace. Another less likely possibilty is that the float is sticking on the side of the float bowl. When you replace the needle make sure that the float is clean of any old fuel residue.

Dont be afriad the take the top off the carb and have a look. Theres not a lot to a vespa carb.

Good luck