2018 FJR AUX Tank Plumbing

[travel_man]

I am over 15,000 miles now with the AUX tank setup and no issues.

 

[natehawk750]

That's great Greg! I'm doing this... I'm not fond of the drilled bung gravity set up I have now. 

@Canadian FJR

This is how my BMW aux tank worked the great thing about this method is that as soon as your fuel gauge lines start dropping you know that your aux tank is 100% empty and can then use the gauge and range properly... when the fuel light comes on its definitely time to look for fuel and it's not a guessing game just to find out that you have another 1/2 gallon left in the Aux tank.

 

[Wistrick]

So I do I take one cap off at a time when filling????   

 

[Wistrick]

Also is it safe to assume that fuel transfer is taking place if the bike isnt acting like its starving for fuel after a few miles????

 

[Canadian FJR]

As far as transfer, I always use a see thru in line filter.  This way I can see if there is fuel and also acts as a pre filter before it hits the sock in the tank.  
 

Canadian FJR

 

[travel_man]

So I do I take one cap off at a time when filling????   

You will be filling both tanks as it would take a long time for the gas to flow to the main tank while you are at the gas pump.

I fill the main tank first and then close the gas cap. I then fill the AUX tank.

 

[Wistrick]

just to clarify I can take both caps off at same time... then fill main tank, close cap and fill the aux tank

 

[Canadian FJR]

This is the only thing that I would be cautious of;

"Do not open the bike tank unless you are positive the aux is empty - otherwise fuel will pour out the moment you open the cap."

Canadian FJR

 

[Canadian FJR]

Just had a chance to try the new setup- worked as described.

I really like the fact that it empties the aux tank first, get rid of any excess weight up top.

I did seem to have a slight bit of fuel weeping around the main tank cap but nothing significant.  I’ll keep an eye on this.

Sure is nice to travel 200 km and still show full bars.

Canadian FJR

 

[RossKean]

I did seem to have a slight bit of fuel weeping around the main tank cap but nothing significant.  I’ll keep an eye on this.

I wonder if you would be better off to start with the main tank filled maybe four fifths.  Then fill the auxiliary. As the fuel comes out of the main, it still draws from the auxiliary but maintains a head space so fuel doesn't slosh around the cap.  Also, I would make sure I valved off the auxiliary when stopped for a period of time. If there is ANY air leak around the main cap, fuel will flow from the auxiliary and potentially cause a fuel leak.  There is a potential problem with this - if temperatures rise,  the main tank would pressurize if valved off since there would be no place for fuel to go.  Assuming I am understanding the plumbing. 

How about a three-way valve?  Straight through when "on". When closed, the auxiliary is cut off from the main but it is still vented normally. The third port on the valve vents the main tank to atmosphere but only when closed off from the auxiliary so a temperature change doesn't create a problem. 

Seems like a safer modification that doesn't rely on a perfect seal around the main tank cover.

Edit:  Just realized that when the main tank is valved to atmosphere when closing off the auxiliary, there would be a small puke of gas since the headspace of the main is slightly pressurized and the line would be full of gas.  Might want to run the vent to the aux tank or to the ground - shouldn't be much volume.

 

[Canadian FJR]

A few 1000 kms and this setup is working great.  A buddy of mine on  a 2004 Gen 1 wants a cell on his bike now.  Any reason that this plumbing method can’t work on a Gen 1?

Canadian FJR

 

[natehawk750]

Just ran a BBG last week with this plumbing set up worked great!

As far as the Gen1 I don't know. I'm assuming if the vent lines are the same then there wouldn't be any reason it wouldn't.

 

[Canadian FJR]

Just plumbed buddy’s 2004 using this method and things are not going well.

He’s getting a lot of weeping around the fuel tank cap rubber flange and no significant fuel transfer.

I’m thinking that no vacuum is being created because of the leaky seal and any transfer is happening though gravity feed and then leaking around the cap seal.

Sound reasonable?

Canadian FJR

 

[travel_man]

Just plumbed buddy’s 2004 using this method and things are not going well.

He’s getting a lot of weeping around the fuel tank cap rubber flange and no significant fuel transfer.

I’m thinking that no vacuum is being created because of the leaky seal and any transfer is happening though gravity feed and then leaking around the cap seal.

Sound reasonable?

Canadian FJR

Yes, I think the rubber gasket is deteriorated after 15+ years. It is / was probably leaking air but you can't see air. 

To be honest I am surprised it is working at all as I did not think FJR's fuel system was a closed loop back then.

I have 25,000+ miles now on my setup with no issues.

 

[Canadian FJR]

Thanks for the reply Greg.

BTW - mine is also working awesome.

Can anyone confirm this "I did not think FJR's fuel system was a closed loop back then"

Canadian FJR

 

[dravnx]

Any chance you plumbed into the wrong line? If you plumb into the gas cap well vent line, fuel will run from the aux tank into the gas cap well and seep up around the cap. 

 

[Canadian FJR]

Well, I thought about that.  Plumbed into the front one same as on my ‘18.  Are the Gen 1s reversed?

It’s leaking around the outside ring, not the actual flip cap.

Canadian FJR