modern fuel filler/breather

[h20hamelan]

I have fit a fuel cap internals, from a newer gas car.
It is a second step to adding fuel, to remove the inner breather cap.
From what I understand, it will release pressure and be sealed for the most part as I have not had the gas tank fully filled yet.
I would like to route the breather system to the filler neck, thus with the modern breather not have a pressurized tank.

I think the use in modern non-leaded gas filler necks with the extra flap which the gas-pump nozzle fits into, would not allow fuel to splash-up to the cap. So the cap fitted with the vent would allow extra pressure out.
I believe the modern fuel caps will allow a little bit of fuel up, but they also will drain back. So on heavy cornering the fuel would hit the metal filler flap, and might splash on the modern breather unit, thus-hopefully the original chrome cap and paint is saved???

any thoughts on this long-winded thought

[Jason1]

Hi

If you are looking for a fuel tank breather in the filler neck then Spyder did this already in the past, see post below:

elan-plus-f13/fuel-vent-t14212.html?hilit=%20filler

Hope this helps

Jason

[vernon.taylor]

Salut

My implementaion of the fuel breather mod with parts used is here:

elan-plus-f13/fuel-breather-mods-t23356-15.html

To note my filler cap rubber seal is in excellent/new condition (I think they can be found new) and I epoxy-glued up the vent hole on the underside (not needed with the breather mod). Not sure if this vent hole is a source of cornering leaks, but I imagine a bad rubber seal is.

I suppose a modern internal-flap would help in these leaky cases - let us know if you find a suitable donor filler - I would look out for a tube that I could cut and slip into the actual filler neck - to be held in either by friction or a suitable adhesive, or the hose-tail fitting of the filler breather mod.

@+

Vernon

[h20hamelan]

as I recall, drilling/fitting/having a hole in the original elan gas filler cap presents the problem of spillage.
so the modern fuel caps (I believe) slow down or stop the sloshing of fuel, with the in-line gas filler nozzle receptacles.
or at least the filler nozzle receptacles I have seen have the metal flap to allow the nozzle, and a small breather hole.

kind regards
james

[stugilmour]

James, I am not sure I fully understand the problem you are trying to solve; perhaps missing something?

I think the general consensus is the vent hole in the Plus 2 filler is vestigial and not required for the system to work as the vent tubes take care of preventing a vacuum forming in the tank and interrupting fuel flow. As Vernon has mentioned, plugging the gas cap vent hole and ensuring the cap gasket is OK should prevent fuel sloshing on to the paint?

Does your proposed system utilize some form of vent lines over the roof line (stock set-up) or a large diameter vent line back to the filler (common mod set-up to allow the fuel tank to be filled when the overhead lines are reduced in diameter)? The common issue folks have with the stock set-up (other than it being in poor condition due to age and materials used) is the large diameter of the two overhead vent lines causing fuel odour in the garage.

HTH

[h20hamelan]

Howdy Stu
Yes, venting to filler neck, and yes ultimately slowing the fuel to the cap.
For a vent to work properly!
I will be testing this theory sometime
Keep yall posted

[h20hamelan]

Salut Vernon

And the problem may be that I have not experienced this car enough.
And that I would not have a problem with fuel sloshing to the cap. Though it seems probable that if filled up. On tight corners fuel could imaginably be at the cap.
I don't like the thought of fuel sitting on my paint.

THANKS!

[h20hamelan]

I thought a old post suggested that without a vent-cap or over the roof breathing system, could slow fuel delivery?
similar to a older motorbike

thanks

[stugilmour]

James, without relatively large diameter vent hoses (say ~1/2" to 5/8" ID) from both sides of the the top of the tank you will be unable to fill the top half of the tank. This is because the fuel filler enters the Plus 2 tank about half way up the side of the tank. The vent hoses in stock form run over the roof structure, presumably to prevent spillage during a roll over event.

The linked thread shows several versions of the popular mod to route these vents back to the filler tube. This is desirable to reduce fuel evaporating from the tank. One post that made sense to me mentioned that the overhead vent hoses set up a vapour siphon due to the straight vertical drop, causing very high evaporation rates. This mod does not get rid of the need to vent the tank during running; it is put in place to allow the air from the top of the tank to be vented out during filling.

The tank still needs some sort of vent hole to stay at atmospheric pressure while the car is running. This can be provided by smaller diameter line from the top of the tank. It can be run overhead in the original routing, or above the top of the fuel tank with the drop tops. The small diameter tube (say 1/16" to 1/4" ID to give a rough impression) does not appear to vent the fuel vapour at such a high rate that your garage constantly stinks. Alternatively, the filler cap can be vented with the pin hole. The issue with the filler cap pin hole is fuel on the paint, which I think was your original concern. With the small ID vent line the pin hole in the cap can be dispensed with.

I think I get what you have in mind with the modern unleaded fuel tube. If you want to try this, I would suggest you may have difficulty if the large diameter vent hose is installed below the flapper; quite a bit of air is expelled during refueling and I think the nozzle and flap will obstruct the air flow more than you would like and reduce the refueling rate too much. This is just a guess though; YMMV. The concern I wonder about is the vent line above the flapper may allow fuel to still slop out the cap. Again, just a guess or something to think about.

HTH

[Bud English]

If plugging the hole in the cap prevents the fuel spillage problem, aren't you just left with the fuel vapor issue? How about sourcing two small charcoal canisters to put inline with the two over the top vent hoses?

[stugilmour]

Bud, I'm not sure of the exact configuration of the design, but I believe a later version of the Plus 2 fuel system (by Lotus, maybe just later Federal cars?) included an air tight cap, an evaporative loss circuit rather than the two overhead vents, a large cylindrical catch tank attached to the fuel tank, a charcoal canister under the bonnet with additional plumbing back to the air box. From drawings I have seen (Section L of my Workshop Manual) it looks like it would take quite a bit of trunk space and add considerable complication. I think the charcoal canisters on modern cars usually have a vacuum tube back to the intake to burn vented fumes and exhaust any fuel accumulated in the canister?

I would not recommend just adding charcoal canisters to the stock large diameter vents because of the possibility of blowing liquid fuel into them when filling the tank. Might work, but I would not try it myself; with my BMW the thing will stink to high heaven if fuel gets in the charcoal canister from overflow due to rapid filling or overfilling backing fuel down the vent line. In my Plus 2 with the vent back to the fuel filler it is easy to blow liquid fuel thru the tube during rapid re-fueling of the top 1/4 of the tank. As I say. it might work as the stock tubes are about a foot or so above the tank and might not back up fuel over the top.

The key point is the fuel venting does not appear to be a big issue with the smaller tube size mentioned in the mod. At least, that is what I have found, and I think the other guys found the same thing. I do have a bit of fuel odour in the boot, but I don't think it is caused by the mod; maybe fuel soaked into the felts over time or the need to tighten up a few connections. I guess a charcoal canister could be added to the small diameter overhead tube if it is a concern, but I haven't found it to be an issue.

HTH

[h20hamelan]

It seems the modern cap internals, allow the small amount of venting is worth more thought. modern cars have been this way for some time now.
Or, could the smaller diameter hose, and only a small section. not too close to the tank, maybe just as it starts to rise. this could slow the off-gassing of vapours.