Tank Capacity

[leafman60]

Ok boys. I had some crossover adapters made for my Scura and I thought I posted some pics 2 or 3 years ago. I had some little spacers fabricated to bolt between the tank and the regulator on one side and the tank and the vallve on the other side. Coming out of each spacer is a brazed-in metal spigot tube to which is attached a flexible hose that runs underneath the spine to the other fabricated adapter on the other side of the tank. This set-up connects both sides of the tank and allows gas to flow between the two sides.

 

The problem is that in order to keep these spacers as thin as possible and avoid them causing interference of the lowered valve and regulator after installation of the crossover spacers, I ended up with spigots of about 3/16 ID. The issue now is that the fuel pump pumps at a rate exceeded the ability of this small of a crossover tube to level things out. At low fuel levels, one side of the tank is momentarily pumped dry afterwhich it slowly refills from my crossover tube and starts supplying fuel to the injectors again. The end result is a run-stall, run-stall. I guess thats better than just going dead in the water but its still a problem.

 

To work nicely, any crossover tube would need to be much bigger than 3/16. In fact, Im guessing a 1/2 line may be the minimum you could get by with. Utilizing a crossover line that big would present many problems due to limited space.

[pasotibbs]

Excellent find! Where do I get one for my own?

I bought it in a car spares shop (Halfords) but I imagine it should be available elsewhere.

[Tom M]

I'm sure this has been brought up before but...on external fuel pump models why can't a tee be added to the supply line by the petcock and the recirc line by the FP regulator, and connect the tees with a section of line under the spine?

[Guest ratchethack]

I'm sure this has been brought up before but...on external fuel pump models why can't a tee be added to the supply line by the petcock and the recirc line by the FP regulator, and connect the tees with a section of line under the spine?

No reason it can't be done. This accomplishes the same as Leafman's idea but does it more effectively, since it uses a fuel hose with larger flow capacity. Trouble with the concept either way is that the "crossover" allows fuel to complete a "short circuit" that cuts out the tank, with a proportion of fuel repeatedly picking up additional heat from the motor and fuel pump with no place to dump it (such as the nice, cool, large heat sink of the fuel in the tank), potentially bringing on earlier symptoms of the dreaded VL. With either setup, since nothing prevents fuel circuit pressure from keeping the RH side of the tank full of fuel (the same as it does in the OE design), not only is the potential for VL increased this way, but there's no benefit in terms of draining the last fuel left in the RH side either.

[Tom M]

I get it now. About 30 seconds after I posted that I realized the problem with that scheme. Maybe I should try and think things through before I post?

[Guest ratchethack]

No problemo, mi compadre.

 

It's a puzzle upon which many (myself included) have invested considerable time, searching for a simple, practical solution. While there are many ways to solve it by extraordinarily complex means, every solution I've thought of and/or read about here involves some prohibitive combination of liability, risk, relatively high cost, and/or time sink compared to the OE config -- and so far, IMHO any such trade-off ain't worth the effort.

 

I reckon we've run up against a Gordian knot that was well understood only after the fact many moons ago by the Luigi's in Mandello (no doubt as well by many other moto mavens all across the planet making the transition from carburetors to fuel injection), and it's one the Luigi's have already "solved" to the most practical extent possible without actually providing another port in the bottom of the tank (which somebody apparently failed to consider even as the designers were sculpting the tank prototype and the first bids went out for production quantities). . . and wot else to expect from a crew manufacturing an obsolete moto in a resort village at the foot of the mighty Dolomites, using manufacturing techniques and parts sourcing methods with direct lineage back to pre-industrial times? . . . but I digress. . .

 

But should anyone here come up with a real solution that's practical, simple, low-risk, provable and sustainable long-term, I'll buy that man a beer or a gallon of fuel, wotever that man fancies the most.

 

Gordian knot

[Skeeve]

Gordian knot

 

You remember how Alexander solved the knot & thereby took the city, right?

[Guest ratchethack]

But of course. Not the kind of solution I'd propose for the infamous Great V11 Lost Fuel Puzzle, though.

 

Alex the Great "simplifies" the Gordian knot