Yamaha 2,5 fuel cap leak water in tank?

[NBs]

Fuel cap leaking rain water into the tank of a Yamaha 2.5. The cap is intact and I have been turning the air screw clockwise and every time it rains I find water in the tank.

New cap or can it be fixed?
It is difficult to understand how water gets into the tank. I had an empty tank in the spring and was about tseking the engine and the surprise was that there was about 1-2 decilitres of water.

NBs

 

[lustyd]

The parts of the cap can be purchased as spares. Before you do that though, I'd remove the tank (pretty easy, just a few bolts) and fill with water to see where the leak is and confirm it's not something else. You can clean the little fuel filter at the same time - it's in the outlet when you remove the fuel hose

 

[B27]

I have a Mariner in the shed, it belongs to a mate.
The fuel tank is cracked around the cap thread.
Rain pools around the thread where the casing surrounds it.
I assume UV has got to the plastic of the tank.
A new tank is >£100.

 

[Aja]

I have a Mariner in the shed, it belongs to a mate.
The fuel tank is cracked around the cap thread.
Rain pools around the thread where the casing surrounds it.
I assume UV has got to the plastic of the tank.
A new tank is >£100.

Exactly the same situation with a Mercury 2.5hp. Unscrewed the cap and the thread detached.

 

[NBs]

Hi,

Thanks for the replies, I checked the fuel tank and there are no cracks or anything.

The only pathway for water is the fuel cap air screw, there is also visible rust on the spring and others.

I covered the cap with plastic film and a rubber ring tightens it around the cap.

Am I correct that the air screw is closed when it is turn clockwise onto the cap surface and open when it is lifted off the cap surface, if I am wrong please comment from you guys, thanks.

 

[lustyd]

yes that's correct

 

[B27]

The crack on the one I've seen was quite subtle, but a lot of water got in!
I guess, every night, the fuel vapour in the tank cools and sucks water in, if it's lying around the crack?
You could pressure test the tank with bike pump or something?

Alternatively, maybe the water was in the fuel can?