Engine dies 20 secs after start

[Geoffers71]

This has got me flummoxed! After priming the carbs so that bowls are full ( level is 41 mm below rim of the cap) the engine starts and runs ok, revs fine for about 20 secs, but then stumbles and dies. Will not restart immediately, but if I wait 2 or 3 minutes it starts ok, revs well, but then dies again after 20 secs. This repeats ad infinitum as far as I can see. I've checked the fuel level immediately after it dies and the level is still ok at 41 mm. I've also removed and checked all the fuel feed pipes and they're all fine. I took out the spark plugs and they look fine too and the spark looks strong enough although I think I will buy a new set in case.
As anyone any idea what it might be? The fuel is 97 Ron with 5% ethanol I expect ( can't buy ethanol free fuel in Devon) and it's probably 2 months old. Grabbing at straws here, but could it be a factor? But then if it was why would the engine start and rev so well in between the issue? Looking for one of you wise men (topical ) to give me some guidance please.
Merry Christmas and happy Elan motoring in 2019

[nmauduit]

you know the saying, 95% of carburetion problems are electrical... do you have electronic ignition? have you tried to swap coil or condensor for a known good one? if there is still the right fuel level when it dies I would look into electrical issues, starting with components that seem warm or hot (esp. if it is always the same 20s duration before the engine dies).

[Elan45]

I agree w/ the suggestion that you have an electrical problem. You should even check that the coil is wired correctly depending on pos or neg earth connection. Got to be something so simple.

Roger

[Geoffers71]

Well !!! Curiouser and curiouser ! Went out to the garage with intention of changing the plugs, but thought I'd give it one more try. Engine started immediately as usual and then....ran and ran and revved and ran normally for nearly 10 mins with no hint of dying Switched off and started again with no return of the original problem, but then noticed that the ignition warning light would not go out with increasing revs. Can't see how that would cause the issues I had, but checked the output from the dynamo which seemed normal ...I think! By this time I'd had enough and gave up any further fiddling for the warmth and sanctity of the house and a hot cuppa.
Thinking about it now I should of course check the control box ( although it was new at the time if the rebuild) and maybe the coil. What else?
BTW. I have Accuspark electronic ignition, Bosch coil and HT leads replaced 12 months ago.

[Gray]

Sounds electrical, although I have had fuel starvation issues that had similar symptoms. Do you have the original ignition cut out switch in the glovebox connected?

[Geoffers71]

Hello Graham
Yes I?m happy it?s electrical too. But what to check next? No isolation switch in glovebox on an S2.
Control box??

[wotsisname]

On a similar vein to Gray's suggestion... Could be a loose connection on the ignition circuit (ignition switch, coil, etc)... Wiggle a few wires with the engine running? (Carefully). Intermittent problems are the pits.

[cobraboy]

Just a thought
I wonder if the old original equipment coil mounted ballast resistor is still there ?
One of these gave me the symptoms you describe, it would heat up and fail, cool and run, heat up and fail.

[Bigbaldybloke]

Sounds like electrical to me. Has the problem cured itself now? If it has, beware it?ll come back at a most inappropriate time! Has this problem just appeared by itself, have you changed anything recently, has the car been out of use for a prolonged period. Usually associated with either lack of use or something just changed. Capacitors have a finite life and can start to break down before failing completely.

[Slowtus]

No expert here but my experience has been that when a car runs for a period of time in this fashion and then dies then the problem tends to be fuel.

Electrical, whether original or enhanced in these cars tends not to work in 20 second cycles whereas as filling depleting a fuel a fuel source may do exactly that.

Then again, I am no expert so...

[Gray]

Geoff

I'm not sure about 20 second electrical fault cycles, but if the carbs are full of petrol immediately after the problem, it sounds electrical. Connections, condenser, coil, coil resistor (if fitted), rotor arm, distributor cap and ignition switch are all potential culprits. If you have a faulty coil resistor to run the coil at 6V in normal operation and bypassed for starting the engine could cut out after starting.

I've got a spark tester and a spare coil, I will need to go to Plymouth later next week, so could drop by. Text/email if you have still got my card, if not send me a PM.

Merry Christmas

Graham

[Geoffers71]

Thanks for the offer Graham, but the original problem seems to have gone away Engine runs fine now I Did pull apart the coil to distributor connections, inspected them (seemed ok) and reconnected. I MAY have disturbed these when I removed the fuel pipe connections to the carbs when I didn't think it was getting enough fuel. These are the braided steel covered type and I always worry about what the rubber pipe itself is like underneath, particularly with the ethanol issue.
However, I still have an ignition warning light that won't go out Ive connected my multimeter across the battery and this shows 12.5 v with engine off. Starting and increasing revs does not change this, so it looks like there's a problem with the dynamo. This will have to wait till after Christmas now, too much to do.
Thanks to everyone for the suggestions. Always helps when you know there's a sympathetic ear out there

[Geoffers71]

Just to finish off this thread. There has been no return of the 20 sec run then dying symptoms and I've no real idea of why!! This in itself is a bit worrying
As for the ignition warning light. I've removed the dynamo (what a pig of a job, but what's new with a Lotus? ) and on stripping found that the commutator was very dirty, but more significantly one of the brushes was stuck in its housing and not sliding as it should. All cleaned up now and dynamo back to charging normally and warning lamp extinguishes as normal. Dunno why that should have happened in only 2k plus miles or so, but glad all is now well.
Thanks again to everyone for your helpful suggestions