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Old 07-06-2013, 04:12 PM   #16
sailah OP
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Originally Posted by joexr View Post
Didn't your flanged fuel pump come from the bottom of the tank?

Yes, but I didn't leave the original flange I needed to remove it because of the shock tower so it's welded shut.
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Old 07-06-2013, 04:13 PM   #17
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Don't you now have a blockoff plate of some sort on the bottom of the stock tank? Where does the fuel line now come out?
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Old 07-06-2013, 04:15 PM   #18
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Originally Posted by joexr View Post
Don't you now have a blockoff plate of some sort on the bottom of the stock tank? Where does the fuel line now come out?
I machined up a tank bung with a NPT tap and welded that to the bottom of the tank
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Old 07-06-2013, 04:16 PM   #19
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I machined up a tank bung with a NPT tap and welded that to the bottom of the tank
And lined it after?
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Old 07-06-2013, 04:24 PM   #20
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And lined it after?
Correct.

I could probably install a bulkhead fitting like guys do on fuel cell equipped mile busters, but every install I have seen they remove the large fuel pump assembly so they can tighten things from inside the tank. I won't have that ability unless I try and line the hole up right under the filler and even that is suspect.
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Old 07-06-2013, 04:29 PM   #21
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That sounds like the only option , short of welding on the tank again.
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Old 07-06-2013, 04:55 PM   #22
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I took apart the fuel cap and you are correct it only vents one way. Why?

I disabled the one way venting system so now it vents both ways and it pulls air around the fuel filler "moat" Hopefully that will allow the main tank to vent enough so that it's not forcing it up subtank vent. Now the question is how to make the subtank vent so that water can't get in from rain.

I think I can form a wall with some JB weld and shove some gas foam down there to keep most of the water at bay.
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Old 07-06-2013, 07:06 PM   #23
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post9-are you quite sure that's a vent? forgive me for asking, but to my limited experence, it looks like a drain for sloppy fueling/rain water. i have wrestled with aug tank problems too, in my case a st1100 with a sampson aux. fender type tank-got it used with NO Installation instructions. the problem sounds like what i had. the cause in my case was that the fuel pump raised the pressure in the tank, and forced fuel out the aux fuel tank vent line.(fist go round it was ventedto the air right above the r. tire. and for a 1/8 inch line, it delevered an alarming amount of fuel to my rear tire) the fix for me was to reroute the sub's vent line into the main, and at the highest point on the main.

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Old 07-06-2013, 09:19 PM   #24
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Quote:
Originally Posted by sailah View Post
I took apart the fuel cap and you are correct it only vents one way. Why?
Letting fuel fumes out is probably prohibited by emissions regs, except via a charcoal canister. That's just a guess, though.

Quote:
I disabled the one way venting system so now it vents both ways and it pulls air around the fuel filler "moat" Hopefully that will allow the main tank to vent enough so that it's not forcing it up subtank vent. Now the question is how to make the subtank vent so that water can't get in from rain.

I think I can form a wall with some JB weld and shove some gas foam down there to keep most of the water at bay.
Another option would be to run the vent line into the main tank through the fuel filler cap. Any spew would just go into the tank. Routing the vent line to the front of the tank would prevent length problems when the filler cap hinged forward to open.

Or, you could [edit:never mind, you'd just dump fuel with this idea.]
There might be problems with both suggestions, but they might also be helpful.
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Old 07-07-2013, 04:46 AM   #25
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Originally Posted by the_gr8t_waldo View Post
post9-are you quite sure that's a vent? forgive me for asking, but to my limited experence, it looks like a drain for sloppy fueling/rain water. i have wrestled with aug tank problems too, in my case a st1100 with a sampson aux. fender type tank-got it used with NO Installation instructions. the problem sounds like what i had. the cause in my case was that the fuel pump raised the pressure in the tank, and forced fuel out the aux fuel tank vent line.(fist go round it was ventedto the air right above the r. tire. and for a 1/8 inch line, it delevered an alarming amount of fuel to my rear tire) the fix for me was to reroute the sub's vent line into the main, and at the highest point on the main.
You are correct it wasn't a vent it was a drain for fuel spills. I hadn't thought about rain water though. Doh! I repurposed it for the vent for the subtank, and it seemed like a convenient spot for it.

I thought there must be a check valve of some kind that would allow air to pas but not fuel and put it in the line.

Anyways if I'm going to keep that line as a vent I will ned to be careful about water getting in there.
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Old 07-07-2013, 04:48 AM   #26
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Letting fuel fumes out is probably prohibited by emissions regs, except via a charcoal canister. That's just a guess, though.



Another option would be to run the vent line into the main tank through the fuel filler cap. Any spew would just go into the tank. Routing the vent line to the front of the tank would prevent length problems when the filler cap hinged forward to open.

Or, you could [edit:never mind, you'd just dump fuel with this idea.]
There might be problems with both suggestions, but they might also be helpful.
Not sure how I'd go about this. I want to keep that fuel cap vent open so that pressure can't build in the tank
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Old 07-07-2013, 09:58 AM   #27
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Quote:
Originally Posted by sailah View Post
Quote:
Originally Posted by hpsVFR
Another option would be to run the vent line into the main tank through the fuel filler cap. Any spew would just go into the tank. Routing the vent line to the front of the tank would prevent length problems when the filler cap hinged forward to open.
Not sure how I'd go about this. I want to keep that fuel cap vent open so that pressure can't build in the tank
I was thinking that you'd take your vent line from the sub-tank and run it underneath the main tank, all the way to the front, then up, over the top and to the filler cap. You'd have to modify the cap to accept the vent hose while retaining the water seal, and retaining proper cap vent operation. I was thinking something like a straight (not 90!) barb fitting bolted/glued into a hole drilled all the way through the cap.

I don't know if your cap has enough space to drill a hole, install some sort of pipe/tube (to prevent fuel seepage, and retain a vapor-tight seal), and glue/weld/bolt a fitting on the top. That's a lot of stuff to put into a fairly small space, and this seems like the biggest challenge to what I've suggested.

On the positive side, you would retain all the original characteristics of the positive-pressure tank, and (hopefully) retain the action of the tank vent. Your sub-tank vent line would be above the max fuel level in places where it's exposed. Areas where it's below max fuel level could be protected fairly easily, for example by using fuel line as chafe gear.

You'd also obtain that awesome old-school race-bike look, with a fuel tank cap with a vent line loop sticking out the top.

I hope that clarifies what I'm thinking about, and good luck with it no matter how you end up dealing with it.
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Old 07-07-2013, 10:52 AM   #28
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I'd try the bulkhead fitting. Maybe on top in front of the cap.
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Old 07-07-2013, 11:21 AM   #29
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things are a bit clearer now-I always say that before sticking my foot in mouth. the expelled fuel over flow is coming from the slop drain( or the fliptop cover), isn't it? clearly the main tank enjoys an elevated operating pressure. ( surprisingly this is normal and part of the design of the bike)- and by extension the sub too! end result is that the gas is blown out the sub and into the slop drain -and if i'm right about that, only rerouting the subs vent line INTO the main will fix it.( i'm not sure if routing to the lower part of the main will do anything for you, except to drastically slow down refueling stops.) this would be the exact same thing I ran up against. piping slightly different, but same problem. if you can't insert a vent into the top section of the main, then you might have to silver solder a tube that goes from out side bottom(hidden from view)- thru the tank to someplace reasonably close to the top. I believe you mentioned that the vent line is an AN#6 this would be the time to make the sub's vent bigger, as well.

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Old 07-07-2013, 10:53 PM   #30
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Quote:
Originally Posted by sailah View Post
Not sure how I'd go about this. I want to keep that fuel cap vent open so that pressure can't build in the tank
If pressure is building up in your tank, your fuel cap is defective.



The way the cap works achieves two things that your system is not:
1) Slow and little fuel spillage in the case the bike falls on its side.
2) Reduce fuel evaporation.

For normal operation, the auxiliary tank needs no vent.
After you run it dry, a manual vent valve will suffice to re-fill it by gravity.
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