Aux tank/Vacuum petcocks

[papanovember]

I just got finished mounting an aux 4 gallon tank on my luggage rack(inside a fiberglass trunk). I also have vacuum petcocks from a XS850. I had to move my airbox forward 15mm because I installed Mikuni RS carbs, and the XS1100 standard petcocks didn't clear(I have a 79F).
Anyway, here's my problem. I want to use the aux 4 gallons FIRST, then switch to my main tank. Short of installing on/off/reserve petcocks(like PartsnMore sells w/adapters), how can I stop fuel flow from my main tank to allow my aux to drain first?
I have cut off the vacuum lines during idle and doesn't seem to affect the fuel flow at all. I had first installed mini ball valves on the vacuum lines which did not stop the fuel at idle. I let it run for about five minutes while increasing revs and did not seem to be starving for fuel. Any suggestions?

[papanovember]

The engine could have been running from fuel in the carbs. I guess the real question is if i cut off the vacuum to the petcocks, will the gravity fed aux tank be consumed by the engine first? This is how I planned on using this setup. Has anyone tried to cut off vacuum to use an aux tank? Should I just switch to on/off petcocks?

[Ljay40]

I'm not sure about the vacum part Papa but I know the local lawn
mower shop has on /off taps that would probally be easier and cheaper than replacing petcocks

[John]

Here is the aux tank idea that I came up with a while back. Maybe it will give you some ideas.
http://www.xs11.com/forum/showthread...=aux+fuel+tank

[HobbyMan]

The XS will ride for a while with petcocks tuned off. You might try to shut off both fuel souces and drain your bowls. If you aux tank is not on and there is no fuel flowing out the drains, then you petcocks are sealing fine. When you get it running well, let us know how it handles with the extra 24 pounds on your luggage rack. That won't damage a frame would it?

[John]

Andrew

Do you remember Skippys' bike when he and Lynda were up here last week? He had it loaded up like a pack mule, and he Lynda was on the back. Doesn't seem to affect his frame any.

[papanovember]

I have not filled it up or set up the plumbing yet. I just got it mounted up and tested the inline cut offs I installed in the vacuum lines. My thinking was, cut off the vacuum to the petcocks, it will use the fuel in the aux tank first. I needed to be able to switch back to the main tank while riding. That is why I put 1/4" inline ball valves on the vacuum lines. That way I could just reach down and turn the valves back on. I could install these cut off valves on the fuel line, but would not be able to reach them while riding.
I still need to test to see if it works, but thought maybe someone had done this and could tell me if I was going down the right path. As for the frame being able to handle the extra weight, I will just have to see...

[HobbyMan]

Just be carefull if your aux tank is full and you want to run on the main, you might end up backfilling your oem tank causing an overflow. That would be dangerous while riding.

[papanovember]

I would always want to use the aux tank first. The aux tank also will have an inline cut off valve. If I used my main tank first, I would have weight and balance issues.

[John]

Weight and balance issues? This ain't an airplane that needs to be trimmed out. Gas only weighs about 6 pounds per gallon. With your weight centered in the middle of the bike, there won't be ay problems.

[81xsproject]

The XS runs just fine on one petcock. Why not put a small pump in the aux tank and run it to one petcock to refill the main tank with a manual pump switch?

[papanovember]

I think there would be a noticible, however small, difference if I had an empty 6.4 gallon main tank and 24lbs of fuel(plus tank and trunk weight) on the back. I also wanted to keep this setup as simple as possible without using a pump. Also, the tank is already built and mounted. On paper, I want to use the aux 4 gal tank first, then use the full main tank that has the fuel gauge. I would gravity feed the aux tank, tee-ed into the carbs, then have the full main. I will try this setup by cutting off the vacuum to the petcocks first, and if that doesn't work, order the Partsnmore setup. Has anyone used the partsnmore adapters and on/off/reserve petcocks?? I am afraid because I have moved the airbox forward 15mm that I will have fitment problems using the partsnmore adapters. I appreciate the feedback from everyone. I am kinda just thinking out loud.

[DiverRay]

Maximan did the same thing with Zilla, and I think he had a post on it. He used a 2 gallon tank, and put a "T" in one line, with a 1/4" shut off valve. He would run the main down for a while, fill up from the spare, and keep going. You could look at that for a second idea if #1 doesn't want to work.