Aux tank larger than main tank

keithu

Premier Member
#22
The multi-cell concept is interesting, but for now I'd prefer the simpler solution of a single-cell tank. A four gallon cell will give me a total range of 350-400 miles which should be adequate for my needs.
 

EricV

Premier Member
IBR Finisher
#23
Sorry I'm late to the party. Lots of suggestions. No one seems to completely understand it all though. Do NOT use epoxy or JB Weld on your bulkhead fitting please. Yes, it's very robust. But you might want to actually deal with that fitting someday. Get a couple of Stat-O-Seal washers from Oil Filter Service Company in Portland. They do online sales. And yes, I've used these in multiple bulkhead fittings with success well over 100k multiple times. https://www.ofsco.net/ (I used to live in Portland) You can double up with one of the Permatex fuel compatible thread sealants for pipe use. 80631 or 85420. Loctite 567 pipe thread sealant also works well.

What has not been well addressed is that a gravity feed system from the fuel cell to the main tank will equalize. The pump guys are freaking out because that method could force fuel into the main tank and overflow it. Gravity doesn't work that way unless the entire fuel cell is higher than the vent line at the cap of the main tank. Odds are that you have an equalization point that allows plenty of safety margin. The volume of the cell is moot. Once the tanks equalize they drain together, staying at the same level.

To everyone that said wait until you're at reserve to open the valve to the cell, err, no. That's how you run out of gas when you still have gas. Transfer rate is not fast enough while you are riding to do this. Ride 100 miles from full, open the fuel cell valve. The fuel will rise in the main tank until equalization point, then both tanks drain together. You're not using a garden hose to connect the fuel cell to the main tank. 1/4" is too small. 3/8" is harder to route w/o pinching it. 5/16" diameter hose works best as a compromise of size Vs flow.

Figure out how you will mount the fuel cell and where the tanks will equalize. Then how much volume in the cell is above that point. That's the amount of fuel that can transfer to the main tank before equalization. As long as you're below that amount, minus about a half gallon for fuel consumption during transfer, you'll be fine. Some experimentation will teach you how long you need to wait before opening the valve. You could likely wait until the fuel gauge drops to half and be fine with a safety margin. You'll see the gauge come back to full as fuel transfers and then it will equalize and start dropping again. When you drop back to half, you'll have half the main tank and a significant amount in the cell still.
 
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Stephen!

Premier Member
IBA Member
#24
What has not been well addressed is that a gravity feed system from the fuel cell to the main tank will equalize. The pump guys are freaking out because that method could force fuel into the main tank and overflow it. Gravity doesn't work that way unless the entire fuel cell is higher than the vent line at the cap of the main tank.
Cannot say I have any hands-on experience with a Yamaha FJ-09, but looking at pictures of one seems to me putting an aux tank "above the pillion seat" would certinly put enough, if not all, of the 5 gallon aux tank above the 4.8 gallon main tank. Enough to cause an overflow if opened too soon.

I do have experience with carrying an aux tank entirely above the main tank and you do not want to open the aux tank until you are absolutely certain there is sufficient room in the main tank. With the K16, the symptoms of overfilling the main tank include the smell of raw fuel wafting about and an extremely rough running engine. When that happens about 20 miles south of Wells at 0230, things get a little clentchy until you figure out what's happening. :eek:
 

EricV

Premier Member
IBR Finisher
#25
Pssst, take the pillion seat off. LINK

FJR Worked just fine for the FJR. Tons of gravity feed fuel cells running around on FJRs. It doesn't 'look' like it would be any different. :)

So, did you learn your lesson about riding a K16? ;) We all work out routines that work for us with the set up we have.
 

Stephen!

Premier Member
IBA Member
#26
So, did you learn your lesson about riding a K16? ;) We all work out routines that work for us with the set up we have.
Reaching down to close the aux tank petcock while dismounting to get fuel is now burned into my muscle memory. So much so that when I rode the '18 back from ABQ, I kept reaching for the petcock (that wasn't there) every time I stopped for fuel. :rolleyes:
 

EricV

Premier Member
IBR Finisher
#27
Reaching down to close the aux tank petcock while dismounting to get fuel is now burned into my muscle memory. So much so that when I rode the '18 back from ABQ, I kept reaching for the petcock (that wasn't there) every time I stopped for fuel. :rolleyes:
BTDT when I changed from the 4.8 Gal fuel cell to an 8.2 Gal expanded main tank. Muscle memory routines stay with you for a while. Like writing gas receipt info down and saving your receipts. It took me months after the IBR to stop myself from automatically getting a gas receipt when I no longer had any need for one.
 

keithu

Premier Member
#28
Cannot say I have any hands-on experience with a Yamaha FJ-09, but looking at pictures of one seems to me putting an aux tank "above the pillion seat" would certinly put enough, if not all, of the 5 gallon aux tank above the 4.8 gallon main tank. Enough to cause an overflow if opened too soon.
I think this is correct. If I actually replace the pillion seat with the aux tank, it could be low enough for this to not be a concern. But I don't think this is a good option. On the FJ-09 the pillion seat must be removed first before the main seat comes off, and the battery and fuses are under the main seat. Thus, if I mount a semi-permanent fuel cell in place of the pillion seat it will be very difficult to access the battery and other critical electrics. Seems like a bad idea.

Something like the Maplefarkles tank would work well, because I should be able to pop the seat up just enough under the tank to then release the main seat latch.
 

keithu

Premier Member
#29
Sorry I'm late to the party. Lots of suggestions. No one seems to completely understand it all though. Do NOT use epoxy or JB Weld on your bulkhead fitting please. Yes, it's very robust. But you might want to actually deal with that fitting someday. Get a couple of Stat-O-Seal washers from Oil Filter Service Company in Portland. They do online sales. And yes, I've used these in multiple bulkhead fittings with success well over 100k multiple times. https://www.ofsco.net/ (I used to live in Portland) You can double up with one of the Permatex fuel compatible thread sealants for pipe use. 80631 or 85420. Loctite 567 pipe thread sealant also works well.
I like this idea, but to be frank I will probably just use JB Weld anyway. I've done it before, I know it works, and I can't imagine why I would ever need to remove the bulkhead fitting from the tank once it's installed.