fuel flow question

[nanardos]

My 78 Elite starts well and drives well for half a mile then it starts slighly backfiring. Then the engine slowly dies and  stalls.

I can start it again after a few seconds but it dies again and so on.

I have checked  the spark plugs, points, condenser, ignition coil, etc and I now suspect a fuel issue.

The electric pump at the rear of the car seems to work well too but I find that the fuel flow that comes out form the fuel pipe - engine / carburettors side - is a bit jerky
I also have an Esprit S3 turbo HCI with two pumps in a row that provide a much stronger regular flow.

I am told that the fuel flow that feed carburettors does not need to be as strong as it is for injection. What do you think ?

[Clive59]

check the filter/gauze inside the fuel tank. Mine got all gummed up, and I had poor flow. Showed up when I was on motorway, doing 60 for a few secs and fuel starvation happened. I just got rid of the gauze.

you should have no more than 3-4psi for an N/A engine

 

[jonwat]

12 hours ago, nanardos said:

I have checked  the spark plugs, points, condenser, ignition coil, etc and I now suspect a fuel issue.

How did you check the coil?

A knackered coil will produce the symptoms you describe.

Next time it happens pull over & check how hot it is.

Too hot to hold means it needs replacing 😀

[Francisco Franco]

I had a similar problem on an Excel, turned out to be the fuel pump, it was on its way out, so worked fine for anywhere between 5-30 minutes then needed a rest.

my late Excel had a factory fitted filter between the tank and pump, I don’t think the earlier cars had this....so maybe worth fitting one if it hasn’t already got one.

Also there is no way you would need two pumps, as you say, a none injection engine is fine with a low pressure pump as long as it is in spec for the carb requirements

Edited May 30, 2020 by Francisco Franco
Added on

[nanardos]

I have put a new coil but it has not solved the problem.

I have noticed that the fuel flow from the tank to the (new) filter then to the pump is rather poor.

The filter is only always half full of fuel, which makes me think that the problem comes from inside the tank as described by John.

Yet, I am not very keen on the idea of pulling out the tank, which seems to be a pain.

I guess I will start by trying to unclog it with an iron wire from outside.

[slewthy]

Breather pipes on tank ok? A negative pressure in the tank could impede flow.

I learned the hard way with my fuel problem - I failed to check each element from the start to the finish. 

[nanardos]

Hi Simon,

Where are these breather pipes located please, they are on illustrated on the original parts drawings I've got ?

[EXCEL V8]

Not all tanks have breather pipes - some breath through tiny holes in the filler caps.

Pete

[slewthy]

Absolutely - I have an old NSU scooter that started, ran but then stopped and refused to run after 20mins or so of running.

The hole in the filler cap was blocked - fuel use created a vacuum that eventually stopped flow until air found its way back in again.

Not able to answer the breather pipe or not on an Elite.

[Drawfiler]

I think you need to begin with fuel flow, take the connection off the carbs and check volume of fuel pumped against time by using a stop watch and measuring jug. Also check the carbs for muck in the float chambers.

if the flow from the pump is poor, check the filters, some are built into the pump, some in the fuel line. The breather problem can be checked by running the car without the fillercap on.

if all this is ok, then suspect the coil.

Peter

[nanardos]

I replaced the original SU pump with a new pump but this has not improved anything...

Someone in the forum mentioned a fuel cut of valve on the chassis around the area of the gearbox.

The car is currently nor near me and I cannot check that now. Do you think this could be the problem ?

[black eclat]

The fuel cut off solenoid is mounted on the chassis rail close to the clutch release arm.

It is wired with a single positive supply with the earth provided by its attachment to the chassis.

I had a problem on my Eclat where the car would run for about 2 minutes and then die. I would wait a few seconds, hear the SU pump run and it would start again and repeat the process allover again.

It tuned out to be a loose earth connection to the chassis. When the car was stationary and engine off, the solenoid was ok.

But the vibration from the engine or the vibration from the roadway was enough to break the connection and cut off the fuel supply.

This meant I could run on the fuel remaining in the Dellorto chambers and then the engine would splutter and die.

Repeat.

Very frustrating to diagnose that problem.

Edited June 11, 2020 by black eclat

[nanardos]

Thanks, your reply is making me hope this could be the problem. I will check tomorrow.

[nanardos]

I have located the part (see pics) and the earth connection to the chassis seems to be OK.

I don't know whether this part is connected to a fuse and whether it's possible to disconnect it and see if the car runs better without it

I guess the best thing to do would be to replace the part but I can't find it neither in the service parts list nor on SJ Sporstcars's website list in the fuel parts section.

What about by-passing it ?

Do you know what that part's actual name is and where it can be ordered ?

[EXCEL V8]

It's a fuel lock - it's there to stop the tank emptying itself via the carbs if you're parked on a hill.  You could bypass it temporarily though to test whether it's the cause of an obstruction.

Pete

[mikeeech]

I used one of these;

https://www.ebay.co.uk/itm/LPG-LPG-Lovato-Benzin-Absperrventil-Solenoid-Valve-Venturi-/302646255866?hash=item46771f60fa

Which is handy since you can open the valve manually if it does fail to at least get you home.

While your there you really should change the fuel line that is compatible with modern fuels. Your line must be approaching 50 years old!

[nanardos]

Thanks, Is that an electrical device ?

Sorry, of course it is ...

[Denis247]

Your picture shows a mounting bolt missing. How did you test the earth is ok ??, did you test it right at the body of the valve? Try temporarily connecting a wire from the body of the valve to an earth,

[nanardos]

Hi Denis,

I did clean the part support and the chassis with sand paper to make sure the earth is OK.

I took the picture before having remounted the missing bolt.

I will bypass the valve temporarily to test whether its the cause of an obstruction as Peter suggested.

I have also ordered the part that Mike is mentioning.