Fuel tank breather arrangement for an EFI setup.

[berni29]

Hi There

Can I please have the forums thoughts on the best breather arrangement for my +2 please. I am using a "swirlpot" as pictured in the boot. One of the fuel tank breather connections has a pipe that runs to the neck of the fuel filler cap as pictured. The other is connected to a long pipe that is open to the atmosphere. This was how I got the car when it was running carbs.

I am thinking that I will have to connect one tank breather directly to the fuel return line. The other breather will have to vent to atmosphere through a check valve (mounted higher than the tank) rather than over the roof.

As far as the swirlpot goes, one connection is the gravity fed inlet for fuel directly from the tank. The pump outlet goes directly to the fuel rail on the engine. So I will only need 2 connections at the swirlpot.

I could run the fuel return to the swirlpot and the overflow from the swirlpot to the non vented breather, but what would the point be? It would be worse because the returning fuel would potentially be warm, and the tank is a lot bigger than the swirlpot.

Many thanks in advance!

Berni

[gav]

Hi Berni
On my Elan, I have a slightly more complicated arrangement because my swirl pot is higher than the tank so I need a lifter pump to fill the swirl pot but the routing is pretty common - tank to swirl pot, swirl to filter, filter to high pressure pump and return to fuel tank. You can return the fuel to the swirl pot but I think it cools better in the tank.
I was told by the pump rep to fit the filter just before the pump but I know views differ on this.
In terms of venting, I have one vent to atmosphere from the tank and because of the lifter pump, I have a swirl overflow that also goes into the main tank.
On the plus two, dont you need an additional breather to the fuel filler from the farthest point of the tank to allow the tank to fill when it is being topped up?
Hope that makes sense and is of some use (appreciate it wont be exact because of the different set up but essentially, the swirl and main tank are vented once to atmosphere).

[elanman999]

Hi Berni,
At first I tried gravity feed to the swirl pot on my +2 but if/when any air gets into the swirl pot the only way out is up past the incoming fuel from the tank. In theory it may work but in practice the air cannot escape until there is very little head of fuel in the tank and there is a lot of air in the swirl pot, you could the hear the air rushing into the tank when this happened. I did have a standard Lotus tank.
In the end I installed standard swirl pot plumbing, that is a LP pump to feed the swirl pot, return from the swirl pot to the tank. HP pump from swirl pot to injectors and the return from the injectors to the swirl pot.

You could try your idea, it's only plumbing to change if there are problems.
Cheers
John.

[berni29]

Hi Guys

Thank you for your thoughts.

How about the following.

Vent the RHS tank breather up over the roof via a braided line and terminating in a check valve exiting approximately where the standard breather would.

Fuel return to the LHS breather

Vent the swirl pot to the fuel filler pipe neck.

One question, would I actually need a check valve on the RHS tank breather? If the car were to end up upside down then fuel would not leak from there, and the rest of the system is (I think) sealed. Is there any point in an inline carbon canister in the breather to remove fuel smells?

Thanks again

Berni

[elanman999]

Hi Berni,

"Vent the RHS tank breather" - I thought that the check valve had to go as near to the tank as possible?

"Fuel return to the LHS breather" -sounds OK.

"Vent the swirl pot to the fuel filler pipe neck" -not bad but when the tank is full it could be under the fuel level?
As a plan it sounds OK to me.

The upside down? but what happens if it's only half upside down? TBH, in a +2 upside down, is not something to think about unless you have a roll cage..

The thing is that a +2 requires more venting on the fuel tank to get a fast fill on the top half of the tank.
Cheers
John

[berni29]

Hi John

Thank you for the reply, I had not thought about it but yes makes sense that the check valve would be near the tank.

The LHS breather vents quite high up on the filler neck, but yes its a very good point about that last 1/3 of the tank being potentially quite problematic to fill.

Also I am going to have to make sure that the filler cap seals really well. I remember years ago on my very first plus 2 the filler cap popping open as I accelerated and a ton of fuel came out like a geyser.

I will start collecting some parts.

All the best

Berni

[spyzee]

Explains all:

[h20hamelan]

Might be overkill, but, a filter before and after the pump helps even out the pump adding resistance.

Following as I am about to change mine finally (4 years later)

[berni29]

Hi

Thank you for that article Spyzee, very helpful indeed.

I was toying with the idea of a post pump fuel filter, will have to think on that some more.

Thanks again

Berni

[berni29]

Hi Guys

Just in case anyone on the same path finds this useful, here is an update.

I have had the engine running and have learnt a couple of things which might seem obvious, but were not to me.

Firstly if you have the fuel return going to the tank and not the swirlpot then the swirlpot will empty faster than the fuel tank can replenish the supply. This is certainly true if the swirlpot is gravity fed as mine is. Also if you have only the main tank ventilated then it will be even slower to fill, so the swirlpot needs a breather as well as the main tank.

All the best

Berni