Tapping into Fuel Return Line on BMW R1200GS

Alan Doak

Premier Member
#1
Hi everyone,

Can someone help me? I'm adding a Tour Tank to my pillion seat. I have a 2005 BMW R1200GS. It'll be gravity fed. I read on another forum about someone else's experience doing this. They drilled a hole into the white flange on the right side of the petrol tank and installed an L shape pipe which ran back to the auxiliary tank.

I'm nervous about doing this even though I can get everything I need from Summit Racing. I have since read that the fuel return line which goes into this flange is able to be tapped into with a T-joint.

Does anyone have an opinion as to whether this is a good option or not? Is this pipe under pressure, and if so does that impact anything that I'm wanting to do?

The picture I have attached is from the web, but it might help explain what I want to do. Any help or advice appreciated.
1200GS_tank_return.jpg

Cheers
Alan
 

OX-34

Premier Member
IBR Finisher
#2
Alan I'm sure there will be BMW people along soon to give advice. In the meantime I have some comments:

- I T'd into the equivalent fuel return line on my Honda Blackbird (fuel injected and with the fuel pump inside the tank) and mounted my auxiliary fuel tank up on the pillion seat. It worked ok. Although the line was under pressure and pumping fuel back into the main tank, I thought that with the head of pressure from the aux tank at some point all of the aux fuel would eventually make its way into the main tank. Judging by the fuel gauge, the aux flow was slow.
The trial worked, but I soon drilled into the main tank and fitted a bulkhead as per the conventional LD wisdom anyway. That would be the equivalent of drilling into that fuel pump plate in your sample photo. The bulkhead method worked better and the aux flow was much faster

I do realise that any flow over 6 litres or so per HOUR is good enough. Apart from perhaps centralising mass or something, I don't think that a rapid aux to main tank transfer is very important.

- Have you considered the vent line instead? On my BMW F800GT and my Yamaha TMax scooter I plumbed the auxiliary tank that way. In both cases the main tanks were completely lower than the aux (F800 is under the pillion seat and the scooter tank is down between my calves).





The main tank vents via the aux tank vent line. One benefit is that it is a low pressure line.

The filling procedure is strict: fill the main tank; close the main tank cap; fill the aux tank; close the aux cap; ride off. Be sure that when it comes time to refuel that you know whether the aux has completely emptied into the main or not. If there is fuel in the aux when you open the main cap then fuel will rush out at you from the main filler (not a huge volume, but enough to startle me LOL). If the aux has emptied fully into the main and you've since ridden farther there may now be an airspace in the top of the main tank that you're not aware of. Choosing to leave the main tank closed and just filling the aux in this case may lead to an airlock, especially in hot conditions.
 

Alan Doak

Premier Member
#3
Thanks Peter - I think the consensus is to drill through the white flange. It sounds scary to me, only because if I make a mistake I'll have a long wait for a new flange to be delivered from wherever they get delivered from. Just need to get my ducks in a row and make sure I order all the right parts!!
 

RFlagg42

IBR Finisher
#4
I agree with Peter. With the GS, it took me about 15 minutes to "plumb" my aux tank. Connect the output of the aux tank to the main tank vent. I did that by cutting the line that goes to the charcoal cannister and using a brass barb to connect it to the aux tank. The fuel pump is strong enough to drain the aux tank as it is using gas from the main tank, which essentially leaves the main tank full until the aux tank is drained. Important: Do not put a valve between the aux tank and the main tank. The vent line of the aux tank is now the vent line for the entire system.

I agree with Peter's filling procedure as well.

Mark Crane has done this with two different GSAs and has ridden countless rallies with this setup. It is easy to return the bike to stock as well. Only problem with this procedure in my opinion is that in really high temps (100+ ?) some have seen vapor lock occur and the aux tank failed to transfer. One can prevent this by drilling a small hole in the gas cap assembly. I know where to do this with the liquid cooled but am not sure how that translates to your model. There's an ADVRider thread regarding an installation of a Camel Tank which talks about the solution.
 

Alan Doak

Premier Member
#5
Thanks RFlagg42 - are you referring to the fuel return line on the right-hand side of the tank, or high up on the left side of the tank? I'm still considering drilling a hole in the white flange, which is ultimately what Peter did. It's scarier, but the flow will be purely gravity fed and I don't have to worry about cutting into a pressure line. For us in NZ the parts for these mods need to come from a long way away and so if I stuff it up then it is potentially a long wait for some spares.

Thanks for your suggestions though.
 

RFlagg42

IBR Finisher
#6
I am not referring to the fuel return line, but to the vent line (overflow ?). On the LC GSA, it is high up on the tank at the base of the gas cap assembly. In a U.S. bike, that line is routed to a charcoal cannister. On non-U.S. bikes, I wouldn't be surprised if it just routes down low on the bike somewhere near the center stand. Yes, there is pressure on that line if connected to the aux tank, but it is very low. I am just using standard 1/4" fuel hose that one can get at any auto parts store.

In the U.S., some people then route the vent line of the aux tank back up to the charcoal canister to make the system compliant with environmental laws. I just route the hose off the back of the bike and leave the charcoal canister out of the loop entirely.
 
#7
Thanks RFlagg42 - are you referring to the fuel return line on the right-hand side of the tank, or high up on the left side of the tank? I'm still considering drilling a hole in the white flange, which is ultimately what Peter did. It's scarier, but the flow will be purely gravity fed and I don't have to worry about cutting into a pressure line. For us in NZ the parts for these mods need to come from a long way away and so if I stuff it up then it is potentially a long wait for some spares.

Thanks for your suggestions though.
Alan Doak, I put a TourTank on my R1200RT and fed the fuel line to a T-fitting I placed in the return line from the fuel pump. I used the one on the left side (High) on the tank. There is no damage or changes to the fuel system or drilling of any holes. The T-fitting can be removed and returned to stock at any time. Realize that with gravity feed the fuel demands at power may not be met with the gravity flow. I ride 150 miles and turn on the aux fuel valve. The fuel gauge seems to hold steady for another 150 miles and then continues to read normally until fuel is gone on both tanks. I did this as I was in a hurry to mount the system before a long ride. It worked so well I have never changed it or had any trouble with it. Also, I did place a flow through fuel pump under the seat in case the fuel looses its prime. You can do it this way for a temp trial and always go to drilling a hole somewhere later.
Here are some pictures of my mounting system. http://ldcomfort.com/mario/fuelcell.html
 

Alan Doak

Premier Member
#8
Alan Doak, I put a TourTank on my R1200RT and fed the fuel line to a T-fitting I placed in the return line from the fuel pump. I used the one on the left side (High) on the tank. There is no damage or changes to the fuel system or drilling of any holes. The T-fitting can be removed and returned to stock at any time. Realize that with gravity feed the fuel demands at power may not be met with the gravity flow. I ride 150 miles and turn on the aux fuel valve. The fuel gauge seems to hold steady for another 150 miles and then continues to read normally until fuel is gone on both tanks. I did this as I was in a hurry to mount the system before a long ride. It worked so well I have never changed it or had any trouble with it. Also, I did place a flow through fuel pump under the seat in case the fuel looses its prime. You can do it this way for a temp trial and always go to drilling a hole somewhere later.
Here are some pictures of my mounting system. http://ldcomfort.com/mario/fuelcell.html
Thanks for this Mario. I've made the decision to drill into the white flange. I'm waiting for the large washer to arrive from the US before I do this. I have the TourTank mounted on an AltRider luggage rack that plus into where the pillion seat would normally sit. I built a raised stand off that with aluminium angles. I'm writing a blog post and will publish here once I have completed the installation.
 

OX-34

Premier Member
IBR Finisher
#9
Alan in place of your Altrider I bolted on a flat sheet of aluminium were the pillion seat would be.

For my flatbed installation I used some 25mm square tube as a stand off as you called it and bolted the tank on top.






My first tank on the Tenere was my old standby JAZ cell. It has a 45mm deep sump, so accordingly the stand offs were 50mm square tube.



It may be very simple engineering, but it has served me well.

Best of luck with your mods.
 

Alan Doak

Premier Member
#10
Nic
Alan in place of your Altrider I bolted on a flat sheet of aluminium were the pillion seat would be.

For my flatbed installation I used some 25mm square tube as a stand off as you called it and bolted the tank on top.



Nice work Peter - I had a great time fabricating my stand. One thing I didn't realise that I need to do is to have the tank earthed. I see in one of your pictures a white wire running to a bolt. Where did you run the wire from on the tank?
 

Alan Doak

Premier Member
#12
Alan, the poly JAZ tank's metal filler neck is earthed.
The alloy tank is all hard bolted, so doesn't need an independent earth.
Ah, makes complete sense. The rest of my parts arrive today from the US so should be back into the installation this weekend. Still as nervous as hell having to drill into that flange!
 

Alan Doak

Premier Member
#14
I finally did it - a couple of months ago actually. Did my first big ride around the South Island in early December. I flicked the switch on the tank and watched my main tank fill – it took about 10 minutes to fill. I yelled, screamed, hooted and hollered with joy. No leaks. Worked like a charm.

The complete write-up is here: http://www.thinman.co.nz/auxilliary-fuel-tank-installation-on-a-motorcycle/
 

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