Gravity fed Aux fuel tank!!!

[VmaxTriker]

Getting a bit fed up with my Vmax's limited fuel range, which is made worse by the way I ride it 

So im thinking of getting a custom Fuel tank to put somewhere on the back, actually thinking about having one made to fit inside a civi luggage box, about 4 or 5 gallon tank.

Can anyone tell me the advantages and disadvantages of doing in the follow way..

Having the Aux tank mounted high to allow gravity to work for me, Aux tank will feed into the main tank through the overflow outlet opening with a tap to turn on and off the Aux fuel, so I can close the tap when I want to fuel up both tanks.

Heres what I dont know.

Will the main tanks fuel supply still function correctly if the overflow pipe is effectively blocked off, my understanding is a standard fuel cap has a breather hole, but the above method will require me to make sure the tanks fuel cap is completely air tight as the aux tank will force the fuel level to rise to the top.

Or if I just close the main tank fuel cap off completely would the aux tanks cap breather be ok, and maybe have a larger diameter pipe going from the aux to the main tank meaning I only have to fill up into the aux tank

not really wanting to go down the route of having another fuel pump for the Aux tank..

Any advice would be appreciated.

[tony b]

why not put a Tpiece onto the pipe that comes from your origional tank,and then the bike will feed from both tanks at the same time giving you more distance between refills,you will still have the reserve on you tank,for emergencies,shabba.

[SUMO]

if you put in a t-piece wont the higher tank drain into the lower tank and then out of the overflow?

[tbone]

It would. The second option sounds best to me, blank the original cap, but don`t ask me how !

[manfred]

Look into how Yamaha did it.
They used to sell one that fitted in place of the false tank, added a couple of gallons.
One turned up on ebay a year or three back, went for silly money.
Of course, you could always just turn the boost off. Maybe run Nos instead?

Would an original venture tank fit?
The filler is at the bottom of the false tank, so an auxilliary should be a push fit.

[morrag]

Check out 'Littlewing',in the Trikes section, which has a main stainless tank at back, an aux. tank under the seat giving a total of 3 gallons or so. The aux. tank drains to the main when required, the main has its fuel pumped, using a Demon Tweeks solid state pump, a tiny thing fitted under the tank, up to a "Weir" tank made from an S.U float chamber, and mounted under the tail piece above carb. level, which are then gravity fed, all works 'tickety-boo', Morrag

[Manky Monkey]

Could you post a photo or diagram of that layout please Morrag, for the benefit of others here.
Oh, &  welcome back mate. Hope the surgery went well. 

[morrag]

Confined to quarters at present Mark, with the missus sitting "shotgun" at the door! but if my son calls weekend I shall try and get him to take a few pics, best I can do at pres. Morrag