1L Swirl Pot Fuel Surge Set-Up Not Working

[Richie-Van-GTi 70 2 Cars]

Slightly disagree with the placement of the pump being the issue here. I pit for a guy running an evo in the saloons which will be pulling far harder round bends than a 205. His pot is inside the car above the tank and fuel pump about level as you have here. I think the problem here is the design of the swirl pot itself. The outlet looks to be not much more than 30mm at most? from the return above it. This effectively gives you a minimal head above the feed if air is induced to the system at any point. Given your highest up feed is on the side and air getting in will collect very easily so the system cannot bleed itself out once in if that makes sense. I would look to replace with a top fed pot with plenty of height and minimal width and all inlets high up. Then do whatever possible to the tank to prevent any air in the first place. Is the current Walbro in a standard housing or is it a homemade pick up system? The standard pumps when in good form are quite hard to surge so coupled with a swirl pot should have no problems on 95% of tracks.

[Richie-Van-GTi 70 2 Cars]

Oops just re read your pipe set up. I thought you had feed at the top. Return to tank at top would allow bleeding out so ignore most of what i said. Assuming it is air though I would still start at the in tank pump. Any air getting into the system must start its journey here. The rest is in effect a closed system once bled through. If the problem definatley a fuel one? Not meaning any disrespect but I have seen seasoned racers with long mechanical backgrounds blaming fuel systems for other issues and wasting a lot of time and money.

[Mac Crash 78 1 Cars]

I pit for a guy running an evo in the saloons which will be pulling far harder round bends than a 205.

 

I think it will be the reverse from experience...

[johniban 59 1 Cars]

Any news on this?

[SweetBadger 91]

Richie, I'm pretty sure it was fuel surge - have experienced it before on track days and it was exactly the same symptoms. Plus I drove the car home from the race with absolutely no issues. Walbro pump is in exactly the same place as the oe pump in the original pump housing.

 

John, no update yet - next race is this Sunday at Snetterton, 1hr again so as long as we make it to the end of the race we'll find out if the problem is sorted. Also I got my swirl pot from this guy off eBay - he doesn't list the top mounted pot but can make one up and it only took him a couple of days to get it to me: http://pages.ebay.com/link/?nav=item.view&alt=web&id=231565599943&globalID=EBAY-GB

Edited July 6, 2015 by SweetBadger

[SweetBadger 91]

Bit of an update - Ran at Snetterton on Sunday, 1 hr race, 1/8 of a tank of fuel left at the end of the race, and no fuel surge :-)

 

We did have some fuel supply issues, but I don't think they were related to fuel surge - occasional mis-firing / power loss. When I finished it was running on 3 cyls and fuel was leaking from the fuel rail, so that's the likely culprit.

 

Also my 2 race old Alternator had also packed in... Incredible!

 

Even so, we won our first trophy - 3rd in Class, and I set the fastest lap in class. Pleased with that seeing as neither of us had ever driven Snetterton before.

 

Maybe I'll get one race this season where something on the car doesn't break! New injector o-rings, another replacement alternator and a new fuel filter on the shopping list for now...

[SweetBadger 91]

On 6/26/2015 at 12:07 AM, SweetBadger said:

Right then, I've run the lift pump with the fuel return from the swirl pump off and there's plenty of fuel.

 

I emptied the swirl pot and it took approx 10 seconds for the lift pump to fill it, so no issues there - that's probably pumping 8-10 times more fuel than is used.

 

The only thing I'm concerned about is that when I pulled the feed to the external pump off to empty the swirl pot, the pot was very slow to empty. The fuel return line to the main tank didn't allow any air to flow back into the swirl pot as the fuel in the line effectively air locked it... The fuel return pipe runs up hill to the fuel tank so I guess the fuel in the return line creates a U-bend effect and prevents air getting into the swirl pot when it is being emptied. As soon as I pulled the return pipe off the pot, it allowed air in and it drained very quickly. Whether this causes any issues in practice I don't know as I'm sure the swirl pot won't be emptied that quickly.

 

Anyway here's swirl pot mk-ii

 

 

The pump is mounted on a couple of nylon rods (not candles) to lower it.

 

The next race is another 1 hr race at Snetterton, unfortunately the first time we're going to be able to test it is in qualifying - what do you reckon will it sort the fuel surge issues?

 

Well 8 years on and I had some rare time to think about an improvement to the return / breather route for this setup.

 

The return pipe run from the swirl pot to main tank return was indeed creating an air lock because of the way the pipe was routed. Down the front of the main tank -> under the tank -> back up to the swirl pot under the boot floor.

 

This was stopping air entering the swirl pot when the fuel supply to it stopped, and therefore preventing fuel from adequately draining by gravity and feeding the external pump. Confirmed by removing the pipe to the external pump and only having a trickle of fuel run out when the swirl pot was full.

 

So I have rerouted the return / breather from the swirl pot so that it can’t air lock:

 

 

 

Used some solid cupronickel pipe (protected by a piece of aluminium tube in the cabin). Goes from the main tank return up to just below the boot floor and then back down to the swirl pot return port. If the supply from the main tank is interrupted, the much shorter and direct run with no u-bend / air lock effect drains back to the tank when fuel supply from the main tank is interrupted - this empty pipe then proves a breather to allow air into the swirl pot so that it can drain easily, which provides a good head of fuel to the external fuel pump.

 

Result! Fuel now pours out of the swirl pot from the bottom outlet to the external pump.

 

Anyone installing a swirl pot should pay very close attention to the routing of the return / breather pipe. If it can get air locked then the swirl pot won’t be effective because the external efi pump can’t draw fuel and will suffer from cavitation should the in tank pump starve interrupting the fuel supply to the pot.

 

 

 

 

[petert 550]

This is mine, with one pressure pump. Being inside the cabin and higher than the oem tank, it's an easy downhill run into the top of the tank. I'm still uneasy about having the surge tank in the cabin, but it is fully enclosed. Ideally, I'd like to throw both away and fit a fuel cell, offset to the passenger side, in a well.

[SweetBadger 91]

Yeah that’s how mine is connected up. 
 

I removed all the fuel lines from in the cabin as likewise I don’t like the idea of fuel escaping into the cabin. Especially with braided lines, you can’t inspect the condition of the rubber hose.

[Biggles 65]

That's why I used a single length of copper line inside the cabin (ok - 2 lengths for feed & return) - PITA to fit but fit & forget.