Alternative Gen I Aux Fuel Cell plumbing

[RadioHowie]

Anyone who's been following THIS thread in "Technical/Mechanical Problems" may be aware that I'm having fuel pump issues.

All the searching and researching I've been doing on FJR fuel pumps here in the forum has led me, unsurprisingly, to auxiliary fuel cell threads, what with the necessary additional plumbing and such involving the fuel pump.

And since the best discussions including fuel pump graphics ARE the aux tank threads, it got me to thinking (danger, Will Robinson!)

Here's what got me thinking...rather than the daunting, and potentially disastrously expensive mistake someone could make screwing up a bulkhead fitting install, this is what I started wondering --

Rather than installing a bulkhead fitting on the main tank, and using gravity or secondary-pump feed from the aux tank, could someone instead do this, to a Gen I install --

Run the fuel return line from the fuel rail back to the aux tank instead of the return nipple on the fuel pump, and then the fuel feed from the aux tank goes to the return nipple on the in-tank fuel pump, completing the circuit.

The aux tank would have to be airtight, so the incoming fuel pressure would force-feed the fuel back to the main tank, but since it IS pressurised, there wouldn't be any venting issues in the aux tank. There might also be a side benefit that the main tank wouldn't heat up as much since the fuel is going to the aux tank before it returns to the main tank, rather than going straight from the hot engine compartment directly back to the main tank. Also, since the return feed to the main tank IS under pressure, from the "back side" of the fuel rail, vapor lock and "aux tank ********" would be a thing of the past.

That's it. Is this a working solution, albeit for Gen I FJRs? It's just a wild-ass idea. Anything wrong with it?

 

[Ignacio]

The aux tank would have to be airtight, so the incoming fuel pressure would force-feed the fuel back to the main tank, but since it IS pressurised, there wouldn't be any venting issues in the aux tank.

Fine idea if you're not going for IBA/rally certification. I believe they require currently vented aux. cells IIRC.

Otherwise I think you're going to have to pressure check everything including fittings, the cell, couplers, valves, etc...probably for the upper rating of the fuel pump you use.

 

[RadioHowie]

The aux tank would have to be airtight, so the incoming fuel pressure would force-feed the fuel back to the main tank, but since it IS pressurised, there wouldn't be any venting issues in the aux tank.

Fine idea if you're not going for IBA/rally certification. I believe they require currently vented aux. cells IIRC.

Never considered IBA certification.

Otherwise I think you're going to have to pressure check everything including fittings, the cell, couplers, valves, etc...probably for the upper rating of the fuel pump you use.

Oh yeah...goes without saying. Oh, and my "idea" simply uses the in-tank, OEM pump as the provider for the entire system. Hell, the pump runs all the time anyway, so there's really no extra "load" on it, other than the pump's running twice as long between gas stops.

 

[FJRay]

Thats the way we used to plumb fuel systems on boats. Run the return from the diesel to a day tank and instead of venting the day tank just run it back to the main and let it vent from there. I don't see why it wouldn't work as long as there isn't to much pressure. If the whole thing is a common fuel system and vented through the stock vent maybe the IBA would consider it safe.

Good thought.

 

[Toecutter]

If the whole thing is a common fuel system and vented through the stock vent maybe the IBA would consider it safe.

Good luck with that. As long as you just want to ride without their endorsement, who cares?

 

[stryg8r]

If the aux tank is pressurized, what is to prevent the fuel transferring to the main tank and then venting overboard?

 

[RadioHowie]

If the aux tank is pressurized, what is to prevent the fuel transferring to the main tank and then venting overboard?

I got this one guys....because the amount of fuel entering the main tank from the aux tank is exactly the amount of gas that was pumped OUT of the main tank to the fuel rails, MINUS the amount of fuel used by the motor.

It would never be more than what left the tank, would it?

I guess, at worse, one would have to put a very low pressure check-valve in the feed line from the aux tank to the main tank to PREVENT gravity feed when the bike wasn't running.

 

[Joe2Lmaker]

It might not pass IBR tech inspection, but there is another problem. Your flow rate from your auxiliary tank to your main tank will be too low (unless the pressure in the return line equals the pressure of the fuel being used).

I would assume that the the pressure in the GenI return line is less than the the pressure of the fuel to the injectors. Your idea would extend the amount of time it takes you to starve the injectors, but I'm thinking you will still have fuel left in your auxiliary tank when you are standing on the side of the road. :dntknw:

 

[RadioHowie]

It might not pass IBR tech inspection, but there is another problem. Your flow rate from your auxiliary tank to your main tank will be too low (unless the pressure in the return line equals the pressure of the fuel being used).I would assume that the the pressure in the GenI return line is less than the the pressure of the fuel to the injectors. Your idea would extend the amount of time it takes you to starve the injectors, but I'm thinking you will still have fuel left in your auxiliary tank when you are standing on the side of the road. :dntknw:

Hmmmm...good point. Idea needs some work.