fuel draining away

[Betared]

If I leave my coupe for a few days the fuel seems to drain back into the tank and restarting can take 10 or so cranks to get fuel up to the carb. Has anyone else experienced this problem and how do you over come it ?
David.

[MattNoVAT]

Yes, I recently had a similar issue.  The vent pipe on my coupe was kinked and after using the car the fuel tank built up a vacuum.  When I stopped the car the vacuum in the fuel tank drew the petrol back from the fuel pipes and it would not start.

I have fixed this problem now.

When you open the fuel filler cap do your sometimes hear air hissing? As the vacuum equalises?

[Neil-yaj396]

You often get this problem with a mechanical pump set up once the fuel in the float chamber evaporates. Any air leaks (opposite of Matt's problem) will make it worse too, I had a tiny crack in the inline filter that caused this. Also if your battery is less than 100% this won't help. The pump only works efficiently on engine power I have found.

[Betared]

Thanks for your replies guys. Today,before starting the car I released the petrol cap slowly and noted that air escaped, i.e. the tank was pressurised.Would an inline non-return valve before the mechanical pump help matters?
David.

[capriblu]

I have the same issue.  Car will restart within a few cranks if it has only been left for a few days but any longer then it seems that fuel has siphoned back to the tank and pump struggles to draw fuel?   I have just replaced pump with another used item that I had and will see whether situation improves.   Should the pump allow fuel to flow back from filter or should it act as a one-way valve?

[HFStuart]

The mechanical pump will allow the fuel to drain back. If it's a problem then a non return valve should help a bit.

[rossocorsa]

I dont think that slightly slow starting is such a disaster at least the oil pressure builds up

[Neil-yaj396]

A worn pump makes this problem worse too.

[joe1999]

I also had a similar issue from the day I recieved the car only to find there was a non return valve on the the fuel tank breather hose that was in the wrong way round leading to the tank no having the ability to release the vacuum. The valve was located in the boot by the wheel well.

Thanks

Joe

[capriblu]

Thanks for the replies.  I had always thought that pump shouldn't allow backflow of fuel?   I am also concerned that float chambers have emptied completely in a just over a week - never experienced this before - perhaps its just a case of putting a warm car away in the garage and evaporation losses rather leakage ........

[Neil-yaj396]

The pump diaphragm can be perforated. It will still work reasonably well but when stood gravity will allow fuel to drain back out of the carb.

[capriblu]

Replaced mechanical fuel pump with a brand new unit and also fitted a manual bulb type priming pump/non return valve just before the pump.  Car will start within a single crank if it has been left for a day but after a week or so it takes several seconds of cranking to fire.  If I manually prime using the bulb the car always starts instantly.

It seems to me that fuel is being lost from the float chamber - where is it going?   Should I worry?

[Thotos]

fuel is being lost from the float chamber - where is it going?   Should I worry?

It's evaporating. Nothing to worry about.

[Neil-yaj396]

Fulvia owners often install an additional electric pump to avoid this problem.

[Thotos]

Fulvia owners often install an additional electric pump to avoid this problem.

I'm not sure an additional electric pump is the way to go. An electric pump connected and not working, in series with the mechanical pump could offer flow resistance. If the electric pump is working all the time then there's no need for the mechanical pump. So changing the mechanical pump for an electric one will overcome this 'problem'. I put that in quotes as I don't see it as a problem! So it takes a few extra seconds to start the engine after it's been off for several days. I don't think that's a problem....  

My Trevi will do this if left unused for several days. Instead of starting with a couple of seconds of engine cranking, it takes 15-20 seconds. But it always starts so I say 'no problem'  

My Fiat 131 (with the similar 2 litre twin cam engine as the Trevi) has an electric pump and if I have not started the engine for several days (or weeks) then the pump clicking sound is different until the carburettor bowls fill up and the pump 'feels' the pressure of the closed needle valves. If I wait for the clicking sound to change before starting the engine, then it starts instantly but it takes 5-10 seconds to fill the bowls.

[MattNoVAT]

I agree with Theo !  So it takes 15 seconds for the mechanically pumped fuel to get up to the carb to start the engine.... The important bit is that the engine still starts!  My Coupe does exactly the same as Theo's Trevi, it usually starts first time and I've never considered waiting a "problem".

Its not a modern car after all. 

[lanciamad]

I dont think that slightly slow starting is such a disaster at least the oil pressure builds up

This is too true, if I ever leave a car for any period longer than a couple of weeks I purposely disconnect the coil and turn it over to build oil pressure before starting. I'd live with it tbh it's actually protecting your engine 

[rossocorsa]

yes in modern cars instant starting is designed in because it is what people want/expect  but it is not necessarily the best thing for the engine. There is a danger in assessing old cars by modern standards

[Neil-yaj396]

Agree that 'problem' is the wrong word, but as above slow starting after being stood for a while is exaserbated by worn pumps etc. I'm certainly not recommending the Fulvia 'fix', just using it to flag up the fact that this is a common thing. As Theo points out we just expect a lot from our cars now modern cars behave as they do.

[capriblu]

Thanks for all the replies;  I feel a little less worried.   I agree that a little bit of cranking prior to firing can be a good thing if it gives chance for oil pressure to build.   However in 22 years of ownership of my car and several other Betas (along the way) all with Weber DAT / DATR type carbs I have ALWAYS found that engine generally fires within a few seconds of turning even if left for an extended period.   I just think finding the float chamber completely dry of fuel after little more than week seems rather odd?  My concerns are that fuel is leaking from the carb somewhere and that it might be finding its way down the inlet manifold?    Perhaps I should stop worrying!