[magnusbrodin]

Hi,
The other day I removed my tank to check the internal strainer at the fuel pump. When I was at it I checked the two hoses hanging under the tank. The larger one was totally clogged and didn't let any air through but after some cleaning it opened up. My question is what is the function of these hoses? Both inlets are up by the fuel cap but outside the sealing rubber grommet so I do not really understand why there are two. If one of them somehow ended up inside the tank it could prevent vacuum in tank but since both are outside sealing rubber it's not the case. Hope my question is clear enough to be able to answer

 

[TwistedMister]

one is tank vent, one is filler overflow and if it's FI one is fuel return.. good to keep them all clear

 

[magnusbrodin]

one is tank vent, one is filler overflow and if it's FI one is fuel return.. good to keep them all clear

It's mostly the vent hose that puzzles me. If it is supposed to vent the tank to avoid vacuum I think it should be inside the rubber seal on the cap. Where it is now it has the exact same function as the overflow tube. You can see the two holes in the picture, one under the hinge and one to the right. I think it looks as if the rubber seal seals where it is bare metal.

 

[BillV]

Go inside the filler hole with a mirror and look for a can-like object near the top of the tank. If it's there, it's a vapor-liquid separator that I think is connected to the vent. A mirror and flashlight will also tell you where the various lines run to.

 

[TwistedMister]

those two holes are the filler overflow.. if you fill too much gas drains out the holes into the hose beneath the bike as opposed to all over your tank..

then there is a vent tube as well vents the tank interior, inside the tank a metal line exit mounts up high where no gas reaches, it's a fume vent...

so the one in the cap area with the 2 holes you show is a GAS overflow drain vent..

the other is the interior fume vent that vents the tank form expanding and contracting so your tank doesn't warp in or expand and crack, both need to be clear with good hose exiting beneath the bike...

 

[TwistedMister]

you will need a mirror and lighting to see the end of the interior tank vent line, it's not visible from filler opening.. some tanks you can see that line with fuel pump off and the tank is upside down..

you should be able to push compressed air through them, it's not a particularly fast flow but with the cap open both hoses should take air..

if not, unclog