Hi Eric...
Thanks for the tips and pointers, I really appreciate the time you've taken to put your thoughts down for me!
This has been quite a journey for us already, for some further background on previous work, including discovery work on how the C14's tank cap, and breather work, check out my SBR prep youtube videos.
https://tinyurl.com/z2ds289r
Why are you setting this up as a vacuum feed instead of a gravity feed system? Your Aux tank is clearly above the level of the main tank. Gravity is a Law, Vacuum is happenstance, (except in outer space).
I do not want to drill my tank.
This is prep / testing for a suitable tank and fit-out to take over to my USA bike, so it's only temporary on this blue bike here in New Zealand.
I have no need for an Aux Tank here, I rarely manage to get to do my LD rides solo here, there are too many of my friends who want to ride together whenever an outing is talked about, and none of them have extended range bikes, so it's pointless me working this into my normal ride here unless I want to ditch my mates...
All of this is to say, that there's a simple way of plumbing into the C14 tank, and it's to use the breather in the tank, the breather is provided into the tank via a maze of chambers in the cap itself, via a rubber female receptacle in the tank's cap area (in the fixed lower surface of the tank filler), which mates with a small male tube in the hinged cap itself. the male portion then goes through a series of maze chambers and valves in the cap beneath the key, and then pass out through the lock mechanism itself into the top, centre of the tank. These valves normally manage controlled positive pressure release and potential overflow if the fuel were able to expand that much, as well as relief of negative pressure build up, using the breather tube feed to draw air into the tank when the head drops.
https://www.wiltshire.net/2022/05/17/concours-1400-fuel-cap-innards-disassembly/
I was able to open this cap up and largely remove all of the valve elements and essentially allow my main tank to breath through the main part of the Aux tank, through the expansion chamber, and then finally through that chamber's overflow. To keep that overflow tube clear, I have added in a secondary fuel filter on the final exit of that breather.
The Aux Tank is higher than the inflow around the cap, and so it is gravity fed, but, it'll also be helped along with the negative pressure created as the fuel head drops, so the short answer is, it's both.
Is the only venting of the aux tank through the top of the filler neck?
Yes, through the vent at the top of the filler neck which then goes to the bottom of the evaporative chamber, which then feeds off the top of that chamber, back down to behind my rear wheel, through a final fuel filter.
Is the line from the overflow catch can on the rear of the aux tank plumbed to the vent line from the filler neck?
Yes, but I'd view it the other way round, the vent at the top of the filler neck being plumbed through the evaporative chamber.
Can you access the valve with the seats in place? If not, consider changing that. (and carry 2 extra fuel filters so you can do field swaps if you get poor fuel)
Yes, I can easily enough either solo, or I could get my pillion to play with it when she's sitting there. It's easy enough to find and use by touch.
Can you isolate the aux tank and still use the main tank w/o making a mess and leaking fuel? (because the main won't work well w/o venting and on a vacuum system, your only main tank vent must be via the aux tank for that to function. This is not true of a gravity feed system.)
Yes, I can either simply shut the valve, and allow a vacuum to build up in the main tank, or I could not fill the Aux tank, and leave the valve open and it'll just have a big, expansive breather system attached. I have run this bike for many many miles when the valves in the cap area were not functioning well and a strong negative pressure built up in the tank, so much so that it was hard to open the filler cap, despite this, the EFI fuel pump was able to pump fuel well enough out of the main tank for the bike to run without me noticing any fuelling issues, because of this experience, I wouldn't be concerned about the notion of running it with no relief for that negative pressure - if I had to shut the valve.
Can you remove the aux tank from the bike w/o leaking fuel? If not, you should consider dry break fittings to allow this. (Not plastic) Possibly kill two birds with one fix and put two dry break fittings, one on either side of the filter, then make up a spare line with dry break fittings in place and a fresh filter in the line. This also potentially gives you an easy way to drain the aux tank if need be, or to share some fuel with a stranded rider.
Sure, we're at very early days of refining this solution. It's not going to get that much use, it's being done for 2 USA trips at this point, a total of ~4 weeks of riding, so I'm keen to keep this as simple as possible, and to keep costs down too... Can I remove the Aux Tank without fuel leaking? A max of the length of fuel in the fuel line between the rear tank, and the breather on the front might dribble out. I thought about T'ing off the main feed with a secondary tap to provide fuel for others, but hey... We could do that with the existing tap, and a spare 12 inches of fuel host if needed...
Connections that do not need to be field serviceable can benefit from
crimp style hose clamps. They don't come loose or require wrapping. One time use, removable and installed with side snips if need be.
I just spent NZ$5 (US$3) per host clamp here for high quality stainless screw based hose clamps, they'll do the job nicely.
Secondary note - Aux tank to valve to filter, not Aux tank to filter to valve. This allows easier swapping of the filter with fuel still in the aux tank.
Depends on what the purpose of the fuel filter is, in my case, it was purely to see if fuel was flowing / see bubbles on expansion return and know if the fuel had drained fully out of the Aux tank into the main one. I wasn't going to put a filter there as the tank is filtered anyway and it's all the same fuel anyway... so... I'm happy with how it's laid out.
Is your aux tank fuel cap tethered? If not, correct that because finding a replacement in the middle of a rally is a big time killer.
Yes, you'll see that on today's video. It's tethered with a chain so that the cap is properly earthed too... I'll also be taking a spare cap along with me too, it'll live in my tank bag or tool kit.
In the SBR I twice forgot to fit the cap when our routine was interrupted, and I could easily have lost that cap during the rally!... (I didn't, it actually never bounced off the Aux Tank, but...)
You have certainly built a stout aux tank. 3mm for the sides and top, 2mm for the baffles with a 4mm bottom would be more than strong enough. The box shape is very strong. Not a negative of your design, just an observation that weight could have been saved there.
Yup, I took advice from Lincoln Seals on the material, so 4mm thick throughout is what we did.
The water jug is still just cantilevered at the bottom. Perhaps a connecting brace from the top of the license plate area to the forward frame. Aluminum tends to crack when it bends and vibration causes stress cracking at the heat affected areas on the edge of welds.
The weight of the jug unsupported by the main frame - it's all supported at the heal of the assembly, assuming the toe is outwards to the back, it's then tied back firmly into that frame with 2mm thick aluminium strap, then further fixed with a material strap too. The rest of that frame, towards the back is purely to hold the number plate and the light which is required here for that to be considered legal.
I'm not worried about this. PS, it's all riveted, and I do check it regularly when I fill the bottle...
The tube bracing from the rear of the aux tank appears to be conduit flattened at the ends. Not sure how I feel about that in terms of corrosion and strength.
It's not conduit, but arial mast supports / stays - they have fairly thick walls and took a fair amount of squishing in the vice to flatten them before I could drill and fit them. These stays are commercially created with that same type of approach, flattening them to then make a mounting point. I've discovered that by angling the vice so that you're not just squeezing directly across the face of the tube, you can create an increasingly sharp edge, without cracking it, so there's still a fair amount of strength left in the zone where it goes from being a tube to being flattened... It's incredibly firm on the bike... It's aluminium, so it's not as susceptible to corrosion as it would be if it were steel, but again, it's one of those things which I keep an eye on.
Regardless of the above, the 'ears' at the rear of the aux tank where the braces bolt up need to be gusseted to avoid cracking and failure. They will crack and break off from vibration over time.
It's going to get three weeks worth of use in the next two years.
This is being done for a very specific purpose, if it gets us through those two trips, and ~22,000 miles, then I'll happily throw this in the bin and start again.
I'm sure all of these points will mull around in my head over the next few months. I have about 3.5 months before this tank needs to be packed up into my check-in luggage and flown over to the USA, then fitted on the bike over there within a 2 day window before we're out on the bikes for a couple of weeks.
