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Discussion Starter · #1 ·
I have been looking and thinking about how to add an aux. fuel tank to my SV for some trips I have in mind.
Ran into an option that seems too easy. This aux. tank, designed for a BMWGS800, simply connects to the fitting where the bike's fuel tank vent hose attaches. Then the aux. tank and it's vent hose act as the vent.
This thing could easily be fitted to a spare passenger seat base.
So the aux. tank is used first and then the main drains.
Will it work on the SV?

http://www.advtank.com/products/bmw-f800-gs-auxillary-tank
 

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Discussion Starter · #2 ·
Wow. 47 views and no one has a thought about whether this may work, understanding the SV's gas tank vent layout.

Maybe I should have titled this "crashed my SV" or "what handgun do you carry in your tankbag?"
 

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Why don't you contact Adventure Tank and ask them whether the tank can be retrofitted to other bike brands and models. I would also go to a BMW parts fiche of the GS tank and see how and where the tank is vented and compare to the 2nd gen SV.
 

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Discussion Starter · #4 ·
Why don't you contact Adventure Tank and ask them whether the tank can be retrofitted to other bike brands and models. I would also go to a BMW parts fiche of the GS tank and see how and where the tank is vented and compare to the 2nd gen SV.
1st of all, they only make tanks for like three bikes. They no doubt will reply with "not recommended" or some shyte like that.
Secondly i have the option to buy this one used. ALL of their tanks work the same way. The fuel is drawn from the aux. tank directly into where the vent hose connects on the main tank.
So thinking it through, the fuel woukd be drawn up the vent tube to the top by the main tank's filler neck and flow down into the tank. This would empty the aux tank first. Their website's installation info says the fuel is drawn into the main tank by the vacuum created as fuel is used.
The actual vent for the combined system is from a separate vent hose attached to the aux. tank.
The more I think this through the more certain I am that it will work.
I have already looked at how it mounts and know it'll bolt right up to a pillion seat base.
I like the big rack on top too. Plenty big for a tent/sleeping bag/pad stuffed in a big Giant Loop roll.

Thanks for your incredibly useful suggestion though.
 

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Do you have a California SV? If so...proceed.:) If not...you might have a problem. The CA tank does have a vent line you could use....the one over by the pump. But if you've got a 49 State bike....your cap is vented so you don't have the vent line you need into the tank.

Thinking about this a little more...I'm not sure it will work even on the CA bike. At least not like they say draining the aux tank first. The vent line on the CA tank goes up to the airspace at the top into a vapor separator. If a vacuum is pulled on the tank, it would pull fuel up the vent tube as long as you hook the feed line directly to the tank. I think. But something seems different here than the BMW's.

Before brainstorming this too much farther....do you have the CA tank?
 

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Discussion Starter · #6 ·
No CA tank for me. I thought my tank had a vent hose as well as an overflow hose. Hmmmmm
 

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Discussion Starter · #7 ·
What if i sealed the vent in the cap, and connected it to the overflow tube under the tank.....
 

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The two hoses that come out of the non-CA tanks (ie 49 State) are both drains, one going to each side of the cap. They do NOT connect to the insides of the tank. You can prove this to yourself by removing the entire cap assembly and putting some air into each fitting...you'll feel the air coming out of each hole.

The challenge will be fitting a feed hose to the tank. I'm thinking you'll have to drill a hole and fit one somehow. You might lose the 'draining the aux tank first' deal, but both tanks should seek the same level as they both drain. It's late, and way past my bedtime so my thinking might be off on this. Will ponder it tomorrow at work when rested.:)
 

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Discussion Starter · #9 · (Edited)
The two hoses that come out of the non-CA tanks (ie 49 State) are both drains, one going to each side of the cap. They do NOT connect to the insides of the tank. You can prove this to yourself by removing the entire cap assembly and putting some air into each fitting...you'll feel the air coming out of each hole.

The challenge will be fitting a feed hose to the tank. I'm thinking you'll have to drill a hole and fit one somehow. You might lose the 'draining the aux tank first' deal, but both tanks should seek the same level as they both drain. It's late, and way past my bedtime so my thinking might be off on this. Will ponder it tomorrow at work when rested.:)
so I plug one of the drains, plug the vent in the cap, and connect the fuel line from the aux. tank to the nipple for the remaining drain hose.

Fact. I fill up so often it's not funny, and RARELY ever overfill or need that overfill drain.

That would work no? The aux. tank fuel would be drawn up and enter the tank from the top of the filler neck.

Here are the intallation instructions. No doubt the F800's vent hose is on the top of the tank. So...all i need to do is get a hose to the top of the tank, and that is what I proposed above, as the drain hose terminates at the top of our tank.....

http://cdn.shopify.com/s/files/1/0108/1992/files/BMW_tank_installation_instructions_new.pdf?326
 

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According to Scott at ADV Tank, "as long as you can modify/adapt the mounting system, the tank should work on any other type of bike". Your initial assumption about contacting them was a bit off. However, as you have been discussing with RecoilRob, Scott doesn't know the venting system of the SV vs the BMW or KTM.

The BMW uses an under seat gas tank. In this diagram, part #5 is the venting source exiting through hose #14.
http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51598
Click on #16 Fuel Supply to the right of the bike picture to view the exploded view of the tank.
 

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Discussion Starter · #13 ·
According to Scott at ADV Tank, "as long as you can modify/adapt the mounting system, the tank should work on any other type of bike". Your initial assumption about contacting them was a bit off. However, as you have been discussing with RecoilRob, Scott doesn't know the venting system of the SV vs the BMW or KTM.

The BMW uses an under seat gas tank. In this diagram, part #5 is the venting source exiting through hose #14.
http://www.maxbmwmotorcycles.com/fiche/DiagramsMain.aspx?vid=51598
Click on #16 Fuel Supply to the right of the bike picture to view the exploded view of the tank.
Thanks for the link to the BMW's tank info. The location of that bike's tank was already known. Logic dictates that any vent hose is located at the top of a tank. So what was learned there?

Actually it sounds like they couldn't provide an answer to whether it will work with a SV. I had already determined that the mounting if their tank to the SV was simple enough. So your contact with them provided what useful information?

I appreciate the effort, but was hoping for more analytical thinking than directive suggestions on who to ask.

And to the question of spending $300 on having another 80-90 miles range being a bad investment?

Try exploring more on your bike.
 

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Discussion Starter · #14 ·
RMan, that last reply souned harsh.I apologize. I know you're trying to help.
 

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No harm done. I don't have the answer since I never owned a 2nd gen, but I am interested in your plan. I looked at the fiche of the '03 tank and noticed that there are two hoses shown. One is a drain and the other says vent. If the tank vents through the cap(usually at the hinge, small hole), then where is the vent hose going to? The first gen tank had only one nipple at the bottom of the tank for water/fuel drain. The CA model has two nipples, one for the usual drain and the other is the vent line to a purge valve/charcoal cannister loop back to the carb or TB. If RecoilRob is correct in that you have two drains neither of which is vented into the tank, I don't see how you're going to use one of them with the aux tank. The overflow fuel drain hole I believe only works when filling with the filler cap open, not closed. So, I don't see how you can back flow fuel from the aux to the filler with the cap in the closed position, unless I'm missing something.
 

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Viewed, but nothing useful to say about the project.
Sounds like a permanent mod, so mod away.

I'd go with a fuel can or two to take along only when needed.
Rotopax seems to have good mounting options.

 

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I'd go with the fuel can. By the time you run through a tank, stretching your legs is not a bad idea, and there are fewer things to go wrong with a gas can, especially one made for the purpose.

I have seen "beer keg as aux tank" articles, but felt that would detract from the looks of my bike.
I do go fairly far afield, and will watch eagerly for any good ideas that crop up here. I tend to fuel at 180-200 miles though, and the density of gas stations in the northeast is pretty good.
 

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Discussion Starter · #18 ·
I already have a passenger seat pan with a Rotopax dual holder mounted that I have used on a few trips. I was looking for a more permanent solution, and this one offered a big rack on top as well.
 

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Neither of the drain hoses connects to the inside of the tank. Their tubes run through it, but unless they are cracked...no fuel will come out. Seriously, pull the screws at 10, 2 and 6 O'clock...take the whole cap mechanism off and you'll see the holes. They are for water (rain or wash) to drain from around the cap or spilled fuel.

Whether you use the stock vented cap or CA non-vented would depend on how high the aux tank sits. When full, if you connect it to the main tank and the fuel level is higher than the main tank....if you keep the vented cap you'll have fuel sloshing out. There is a check valve affair inside to help prevent this (I think that is what it was when I had mine apart) but constant over-filling will likely result in a leak.

Even the non-vented CA cap might not hold fuel well enough to not seep. Wasn't really designed for that...just holding vapors in check. Even if the aux tank is lower than the main, you have the opposite problem of full main flowing out of the aux. This is if you add a connection to the main tank and run a line from the aux. Without the BMW's venting system I don't see that automatic type operation happening.

But, all is not lost! Actually, the solution would be a simple manual valve in the connection line. This is assuming (looking at my bike) that your aux tank will be up pretty high compared to the main. Fill both tanks with the connection valve closed. Run the main down to the warning light. Open aux tank connection valve and it should pretty much drain into the main until empty...and if it doesn't drain fully, you should be able to keep the valve open and run both tanks until you run out of fuel in both. The aux tank should empty before the main runs out....if you put the new bulkhead connection on the new tank down at the bottom as low as possible.
 

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The lowest point on the auxiliary tank must be higher then the main tank cap.
I've had F650 BMW's, and rigging an aux tank was easy on them.
On the SV, you might "glass in" the lid of a large top case, but nothing lower would work.
 
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