Carb leak

[DaveyT]

I would agree with Andy. 

The test I suggested was really to confirm that the pump DOES shut off with sufficient  pressure, hence removing it from the mix.

If so, and the pressure drop is beyond the solenoid, causing overfuelling, then it is has to be something in the carbs.

out of interest Brett, was the gasket under that too cap a full area fibre type, or did it have passage ways cut into it? The one for the Turbo has holes, while the NA one is solid. Don’t think this changes your issue if pump still running, but it could allow splashback through the vents in the black cap?

re-reading earlier suggestion, just unplugging the live from the stop solenoid to test the pump should avoid the need for clamping hoses IF the solenoid is working.

[jcslocum]

On 22/04/2020 at 04:41, jonwat said:

No regulator on an NA motor. 

Yeah, yeah, yeah. Don't confuse me with the facts!!!

[Big Vern]

I have the dash out at the moment with wires everywhere so im not ignoring all the suggestions i just cant start the car yet until i get it all back in. I will update on the suggestions shortly. Thanks folks

 

[Big Vern]

On 23/04/2020 at 10:20, DaveyT said:

out of interest Brett, was the gasket under that too cap a full area fibre type, or did it have passage ways cut into it? The one for the Turbo has holes, while the NA one is solid. Don’t think this changes your issue if pump still running, but it could allow splashback through the vents in the black cap?

It is a full one with no passages....

Also i clamped the hose yesterday to see if the pump stopped but it kept running....

[andydclements]

Is it the right pump? There are versions with different operating pressures (even twin ones) but I'm not sure if the single ones can be different pressure also. Not that the wrong one should keep attempting to pump when the line is completely blocked by means of a clamp.

[Big Vern]

Ive never changed the pump myself so im not sure, maybe it was changed by a previous owner. 

[ekwan]

On 07/05/2020 at 18:09, andydclements said:

Is it the right pump? There are versions with different operating pressures (even twin ones) but I'm not sure if the single ones can be different pressure also. Not that the wrong one should keep attempting to pump when the line is completely blocked by means of a clamp.

AFAIK there are only 2 types of pumps that can be used for an NA S3 Dellortos. They both run at a maximum pressure of 2.5 psi and supply sufficient flow for a 160bhp engine.

There may be other pumps that fulfill this requirement but  I am not aware, but like to know if they exist.

[drdoom]

There are certainly a number of pumps which can be applied to fueling carbs of any sort on any automotive engine. If not designed with regulation to the desired pressure an external pressure regulator may be readily added to adjust. Piece of cake.

[ekwan]

12 hours ago, drdoom said:

There are certainly a number of pumps which can be applied to fueling carbs of any sort on any automotive engine. If not designed with regulation to the desired pressure an external pressure regulator may be readily added to adjust. Piece of cake.

Good choices of pumps out there that will operate up to 5 psi and can be used with a FPR. But if you are trying to retain originality in an S3 NA.......

[andydclements]

I asked regards type of pump in case it had been replaced with a non-standard one which could be the cause of the problem (such as then required pressure regulator having failed). If it's standard then I think it's back to the carbs and the float/needle arrangement such a tiny piece of debris.

[Big Vern]

Im going to purchase a fuel pressure guage, Ive also tried looking in the service notes for the correct fuel pressure for a N/A but cant find any details. Does anyone know what it should be?

[ekwan]

2 hours ago, Big Vern said:

Im going to purchase a fuel pressure guage, Ive also tried looking in the service notes for the correct fuel pressure for a N/A but cant find any details. Does anyone know what it should be?

Below 3 psi for sure, hopefully not 2.5psi. Idling around 0.8-1.0 psi at the furthest carburettor.

Edited May 12, 2020 by ekwan

[Big Vern]

Ok thanks Eric much appreciated 

[ekwan]

1 minute ago, Big Vern said:

Ok thanks Eric much appreciated 

I replaced my fuel pump about 4 months ago. I couldn't tune the engine to idle after revving. Fuel pump was only developing 0.1psi.

Symptoms of blocked idle circuit. Pressure gauge was a saviour. The replacement pump was either a AUA25EN or AUA66EN, unfortunately I am stuck overseas unable to travel home due to the COVID-19 situation. Else I can look which pump I have.

[Clive59]

This works perfectly well on my 912 engine ELite.

https://simonbbc.com/fuel-flow-su-replacement-fuel-part/

Designed as a modern replacement for the SU pump

Also, I had fuel starvation when at speed for a while, and it was the filter inside the fuel tank. Just another thing to think about. Good luck with it

[Big Vern]

Took a quick pic of the pump, looks like it might be fairly old anyway......

[ekwan]

They've gone electronic now 

[Big Vern]

21 minutes ago, ekwan said:

They've gone electronic now 

Yes i have a new one being delivered from SJ

[drdoom]

5 hours ago, ekwan said:

Below 3 psi for sure, hopefully not 2.5psi. Idling around 0.8-1.0 psi at the furthest carburettor.

Don't see how to make sense of this. The fuel line must surely place carb inlets in parallel to each other, therefore whatever pressure exists at one must be the same at the 2nd. Why on earth would one expect carbs to function correctly with differing supply pressures?? Why will pressure be diminished at idle?? 

[ekwan]

10 hours ago, drdoom said:

Don't see how to make sense of this. The fuel line must surely place carb inlets in parallel to each other, therefore whatever pressure exists at one must be the same at the 2nd. Why on earth would one expect carbs to function correctly with differing supply pressures?? Why will pressure be diminished at idle?? 

That's the official line from the factory manual. I guess if the delivery volumes/pressures are insufficient, the effect would be magnified at the 2nd outlet.

Edited May 13, 2020 by ekwan

[ekwan]

11 hours ago, drdoom said:

Don't see how to make sense of this. The fuel line must surely place carb inlets in parallel to each other, therefore whatever pressure exists at one must be the same at the 2nd. Why on earth would one expect carbs to function correctly with differing supply pressures?? Why will pressure be diminished at idle?? 

Fuel supply is in series, if original factory.....at least it is on my one owner vehicle. This is what it looks like on my engine (pc taken from another post).   

 

 

Edited May 13, 2020 by ekwan

[drdoom]

Illustrates my point quite nicely, as that is a parallel distribution arrangement affording each carb an equal go at the fuel supply/pressure. Parallel/series terms are not typically used to describe fuel systems as they are always a parallel layout, in accordance with my prior observation regarding pressure at the far carb. This is fluid dynamic theory at its most elementary.

[Big Vern]

So ive had a new fuel pump fitted from SJ's and it ticks and then stops, also no leaks. Silence at last. I did however take the old one apart to see if there were any problems and i couldnt see anything, no tear in the diaphragm and no obvious issues. Oh wwll at least its sorted (for now) 

[Choppa]

Glad you got it sorted!

[ekwan]

10 hours ago, Big Vern said:

So ive had a new fuel pump fitted from SJ's and it ticks and then stops, also no leaks. Silence at last. I did however take the old one apart to see if there were any problems and i couldnt see anything, no tear in the diaphragm and no obvious issues. Oh wwll at least its sorted (for now) 

If your old pump has contact breakers, it could well be that the points have burnt, worn, or they need re-gapping. Perhaps other issues etc. 

 

Glad you sorted out your issues for now.

Edited May 22, 2020 by ekwan