Fuel tank shenanigans

Right then I seem to be having some issues with fueling and my new fuel tank.

I've st it up for bike carbs, so I have tank, filter, bike carb pump (electric) the carbs. No return line from carbs back to pump as its self pressure regulating.

All lines are new and 10mm od copper or 10mm id rubber flexi lines. Return line is attached to the sender unit but is capped off in the bay as it's not required for the current set up.

The breather pipe and the lines to the ball thingy were all replaced with new as well.

When I filled the tank before the mot, fuel came running out of the top of the tank from the sender as it appears I'd caught the sealing ring when putting the sender back in. Sorted that.

During the day as the air temp rose fuel began running out of the very thin pipe that runs along the edge of the tank. When I opened the fuel cap I got a rush of air and the fuel stopped running out. This happened on 2 consecutive days.

Today I went to a show. Upon starting the car, fuel was coming out of the flexi lines to hard lines on the carbs. I had to tighten all the jubilee clips as they were all loose. Odd, as I'm sure these were checked and double checked and there had never been a leak here before.

On my way back (about 10 miles) car began to splutter and loose all power. The pump was also going beserk and the flexi lines felt like they had no pressure in them.

If left for a few minutes, she'll kinda splutter into life a bit.

It's almost as though there is a vapour lick somewhere.

Any thoughts?

Ian

I would start by checking the gravity valve up by the fuel filler neck. After having a few shenanigans of my own recently on a 1.8GTI I discovered that the gravity valve is the fuel tanks breather to allow air in as the tank empties through use but allows a slight pressure in the tank from expansion as the fuel warms up but releases it before it builds up too much. Mine was sticking and building up a lot of pressure so I got a big whoosh and fuel spitting out of the filler neck. A replacement valce sorted this.
If you take it off you should be able to blow through it both ways when it's upright but not when it's upside down.
See how you get on, if you need any other info let me know and I'll dig out my old valve and see how it works exactly.

Ta, I shall have another look at it. I had a quick look last time it started playing up, but it seemed ok.

Ta

Ia.

I just checked my old one. It appears to work ok some of the time and then it seems like the ball inside gets stuck and closes off the vent.
If you look at the valve the top outlet should say open which goes to the trumpet looking outlet that's clipped to the tank and the other is marked tank, this one goes to the tank just in case you were wondering     !
If you blow into the top one it should be virtually unrestricted until you tip it up and then it closes. If you blow into the bottom one it should be restricted but if you give it some puff it should let you blow through it and again, if you tip it it should block. It should unblock again once upright and this is where mine had failed, once it had blocked while under pressure (presumably from going over bumps and maybe surges of fuel going up the breather) it wouldn't release again until the pressure had dropped. I was also getting fuel spurting out of the trumpet breather occasionally, normally after an enthusiastic drive   !
I hope this helps and I hope you get it sorted soon!
Matt.

Thanks for the advice chaps.

Checked everything yesterday and all seemed fine. Blew through the ball valve and exactly as described. Pipes all seemed free with no kinks.

Sorted out the suspension to get rid of horrible reveese rake and cambered.the front wheels correctly, checked the plugs and they had oil on them! Cleaned off said oil and then took for her for a test drive.

After about 10 minutes or so of enthusiastic driving, broke down again.

Thought maybe ran out of fuel. Went got some. Pit about 12 litres in and it was coming out top of the filler.neck so totally full.

Couple of people stopped to help me out (some nice people still out there!) So we checked spark (yup, possibly a bit weak but still got one of each plug) checked wiring, all seemed ok. Phoned AA.

Whilst waiting for AA I has another look im the filler neck, fuel level had dropped. Shook the car about a bit and it would drop a bit more. By the time the AA arrived 3 hours later the fuel had dropped out of sight in the filler neck.

Finally arrived, he thought fuel issue as she'd kinda run on 3 cylinders. Fuel pump was also going crazy.

He checked the filter and it has rubbish in it. Suggested changing it, just to see. About a litre of spilled fuel later……

Lo and Behold, jumped into life.

Drove home, about 5 mins with no issues.

Now then, this seems odd to me as its a new tank, new filler neck, all new rubber pipes (including breather pipes), the only thing that isn't new is the pick up in the tank, which wasn't great but was cleaned out and seemed serviceable. The fuel filter wasn't full of rubbish but did have rust in it. (It's before the pump).

Could it be that by breaking the system and allowing fuel out, somehow a vacuum or pressure build up was released or could it simply be a bit of rust blocking the outlet of the filter?

Btw my breathers are all rubber pipes, not hard plastic.

Or am I fixated on a vacuum problem that isn't there?

Cheers

Ian

I would suspect a vent line or the Gravity Valve, Possibly the Check Valve.

It isn't uncommon for disturbing the fuel system of a car to knock rusty bits loose and stop filters or pumps.

The fact that you shook the tank, and the level went down is more of the issue and why I think it is a vent line, or gravity valve, as that is the purpose of them to prevent things like fuel splash on fill.

I know that when I replaced the fuel filters on my digi, I had clear fuel from the outlet to the pump and ugly blackened fuel from the inlet to the filter from the tank which led me to replace the hoses from the sump/swirlpot/filter and tank, as that was a sign to me of rotted fuel hoses.