Every now and then I get a sucking sound coming from my vented gas cap. It's loud enough to where I can hear it a couple feet away from bike. So I walk be to the bike, open the gas cap til I hear the air "rushing" then tighten up. and sucking sound gone. It doesn't happen all the time. I have a stock 1989 FXSTC. Well, stock except I replaced the butterfly with a CV a few years ago.

 

Make sure your vent line is clear and not pinched anywhere.

 

that's the tube between the tanks correct?

 

No, the vent hose runs from the top of the tank down to the bottom of the frame.

 

There are two tubes "between" the tanks. The one underneath the front of the tanks allows fuel to flow from the right tank to the left. The upper tube (under the instrument panel) allows air to pass from the left tank to the right as the fuel flows from right to left.

The vent line is under the instrument panel, near the right side gas cap. It runs rearward past the battery and, on my bike, runs into a vapor valve then terminates on the swingarm.

 

 

I can imagine that when you park your bike on the jiffy, the fuel in your tanks will level itself out, so there will be a movement of fuel and hence air between them. Is the sound you hear as simple as that? I've never owned a twin-tank bike, so haven't experienced what they may get up to when we walk away!

 

I can't hear the fuel leveling out of either of my twin tank bikes when I park them.

 

OK, you guys got me confused. I've got a tube under the instrument panel (I always assumed was to vent the left tank), and I have a tube under the tanks (which I always assumed was to carry fuel between the tanks.
then on the bottom of the right tank, there is another "nipple" if you will that doesn't have anything on it (I assumed to this point was the vent for the tank).

However now you guys have me thinking. I've see in places on this forum where people are saying this part could be soldered shut (except for Cali), it's fine the way it is, or this is where the tube should go that goes back behind the tranny.

 

On my Glide I have two drain tubes from under the tank panel: one is for draining away spillage when filling the tank; the other is for draining away over-fill of the tank, such as when the tank is full and sitting in a hot sun.