Twenty Minutes Then Nothing...

[gjz30075]

Don't think they're adjustable. Pull them apart and check for dirt and gunk. They might need replacing. It's been a while since I've had them apart but I think there's a gauze type of material in the inlet. Check for dirt there, too.

[RedS4]

Hmm... That sought of thing was supposed ot have happened when the carbs went to a specialist in September - They were fully stripped, overhauled and cleaned.

[AHM]

Do you have a steel tank or an ally one?
Do you have an inline filter?

[ericbushby]

Evan,
Please tell us which type of carburettors you have. It is difficult to come up with ideas without knowing that.
For instance I know that Webers should have a strainer in the inlet which could be blocked but I know nothing about the others.
Remember all faults are easy afterwards.
Eric in Burnley
1967 S3SE DHC

[rgh0]

Sound like you may have the carb inlet strainer blocked in the rear carb.

cheers
Rohan

[RedS4]

The carbs are webers. I pulled out the strainers and they looked fine. But I will have another look after last night's debacle.
Managed to lose one of the float chamber cover plate retaining screws as well - and yes I had tightened them down..
BTW the tank is stainless steel.

[billwill]

The needle vlave is lifted by a lever operated by the float. When the carb has the correct level of fuel in it, the float lifts the valve and closes it preventing more fuel getting in.

The fuel level is adjusted by carefully bending the lever so that it closes the valve at a different fuel level.

Presumably they fitted new needle valves when they serviced your Webers; looks like when they get warm they are sticking instead of falling open cleanly .

[RedS4]

Thanks Bill. I will investigate that, bearing in mind it was having this problem before the carbs were serviced....

I have been offered another theory that the generator is on the way out - the NRMA tested it as delivering only about 13 volts at best - the capacitor is failing; so it might be worth considering an alternator as part of the process...

[billwill]

Thanks Bill. I will investigate that, bearing in mind it was having this problem before the carbs were serviced....

Maybe they didn't change your needle valves and that is still the cause of your problem.

The tips of the needle start off as a cone, but over time the mating surfaces wear down and create a lip near the point of the needle. I suppose there is a faint chance that that could jam.

I have been offered another theory that the generator is on the way out - the NRMA tested it as delivering only about 13 volts at best - the capacitor is failing; so it might be worth considering an alternator as part of the process...

Unlikerly to cause your symptoms; The engine will run for an hour or so on a fully charged battery that is not being charged by the generator, before it has too little power to raise a satisfactory spark.

And the battery would be too flat to turn the engine over even after a rest period.

[JJDraper]

Could try the ballast resistor - only in circuit during running, not engine cranking with starter. See my post a few weeks ago - similar symptoms.

lotus-electrical-f38/engine-just-died-coast-stop-t32852.html#p221625

Jeremy

[RedS4]

Hi Jeremy
At the risk of showing my ignorance, I don't know where that is or what it looks like . Any pics?

[JJDraper]

Here is a pic of the Ballast resistor on my car (RHD +2). The purpose of this is to limit the voltage to the coil during normal running to around 8 to 10 volts, rather than the full battery voltage of 12-14 volts. The ballast resistor is out of circuit when the ignition switch is in the starter position, and drops back into circuit when the ignition key is in normal engine run position.

The reason for this is to allow the coil to 'boost' the spark the help the engine start, but once its running, the coil only needs the lower voltage to operate correctly. The higher voltage puts more strain on the coil, leading to premature failure, if its a coil designed to run on a ballasted ignition circuit. Some people remove the unit thinking the higher voltage will cause bigger sparks and hence more power.... It may do for a while, but an overheated coil will be the result.

The use of incorrectly matched coil/ballast resistor can cause problems, especially when you are unaware of what you should have! To get you home, it can be bridged/shorted across (the two white terminals on my car) with something like a paper clip, as I did. Replace as soon as possible if faulty - In my experience in the previous link, I think the unit had been failing for many months, as the car would occasionally hesitate/cut out, then pick up again. I thought no more about it until it failed completely... Easy fault to try & eliminate if you are stuck - paper clip! If it doesn't work, at least you know what problem it isn't...

Jeremy

[RedS4]

Ah well, I replaced that quite early on as I over-tightened the bolt holding it in place and shattered the casing. I have glued it up to keep as a spare. In short, that's not the problem...

[Craven]

You say you rebuilt the fuel pump, have you checked the delivery pressure?

[RedS4]

Yes - whilst I cannot actually quantify the pressure, I can say the fuel flow is quite good