Aux. Tank flow problem

[B.D.F.]

I don't think the vent line willing with gasoline would be a problem- gasoline is very thin and has virtually no surface tension so it will not cling or clog in a tube like water would. I think it would clear itself as soon as the level in the main tank dropped enough to clear the end of the vent tube. And even if it did not, as the level dropped in the main tank the differential pressure would increase (due to the increasing difference between the two tank's levels) until the vent line did clear. At least that is how I believe it would work but I would have to test it to verify that.

Still, if you just wait until the main tank is low enough to accept the full volume from the secondary tank, the vent line idea will work very well.

The last thing you could try would be to just see if the aux. tank will flow enough fuel into the main tank to drain the aux. tank with the bike running and the main fuel tank cap closed. You said it fills very slowly like that but the bike uses fuel very slowly too so it might work out OK if you wait until, say, the main tank was 1/2 empty and open the transfer line valve. The very worst thing it could do was simply to not work fast enough and cracking the cap on the main tank will always fix that.

I do not think that fuel sloshing will be a problem with foam in the aux. tank even when it is around ½ full. There is no real side- to- side force generated when riding a motorcycle anyway and a bit of fore- aft sloshing will not be a problem. As riders sitting relatively unattached on top of motorcycles, we tend to ‘slosh’ fore and aft ourselves due to acceleration and braking anyway. 

Brian

Thats what I was thinking, if the valve got opened to early to dump the load the internal vent would be covered with fuel and with it tied to the aux tank vent it would cause the same situation that I am trying to remedy right now. I could not imagine that the gravity fed fuel coming into the tank would push the fuel uphill back to the aux tank and continue to fill the main tank. In fact now that I am thinking/writing it, if fuel got into that "return" vent line it may cause another problem.

[4cedars]

I am going to stop at FASTENAL and see what is available for the vent tube in the tank. If I remember when I pulled the pump to install the bulkhead fitting there were small tubes inside the tank from the factory. I may be able to secure my vent tube alongside those. I cant remember exactly how they ran I just remember seeing them. The engine uses fuel faster than the aux tank will replenish it in the current form, as I figured out yesterday. John

[B.D.F.]

That is a great idea- attach your new vent tube to one of the vent tubes already brazed into the tank. Both vent lines go from the extreme back of the tank (where the rubber tubes connect, under the saddle) to the area immediately around the filler cap (or as it is humorously known around here, courtesy of Haroldo, 'gashole').

Brian

I am going to stop at FASTENAL and see what is available for the vent tube in the tank. If I remember when I pulled the pump to install the bulkhead fitting there were small tubes inside the tank from the factory. I may be able to secure my vent tube alongside those. I cant remember exactly how they ran I just remember seeing them. The engine uses fuel faster than the aux tank will replenish it in the current form, as I figured out yesterday. John

[4cedars]

Thanks for being a sounding board on this Brian, it is appreciated.  John

[B.D.F.]

Glad to be of any help that I can John. Hope it works out for you. I have gotten some excellent information and ideas from this forum so I try to give a bit back where I can.

I am thinking about doing something similar and so was already thinking about the whole fuel transfer problem.

Brian

Thanks for being a sounding board on this Brian, it is appreciated.  John