Engine stalls after 3-5 secs (and has very sooty plugs)

[pmansson]

Can an excessively rich mixture cause this???
I see in the car’s Blue book that I increased the the CO level from 3 to 5,5 using my nearby garage’s tester, following a brake fluid change.
Next time out, a week later, the engine stalled when warming up. Yesterday I had a bad drive with lots of starts and stalls. I took out and cleaned the plugs. It starts on first but stops after a few seconds.
Can it be that the tester was incorrect and what I read as 5,5 is actually very much richer causing the sooty plugs?
Can it be so rich as to cause the engine to stall after 5-7 secs?

[cactusman]

Might do. Over rich mixture may flood the engine. Very sooty plugs are an indication of poor combustion due usually to a rich mixture and lots of soot prevents the plug from giving a clean spark which makes matters even worse. I'd say your carburettors need setting up correctly.

[pmansson]

The carbs are in very good shape. New jets in August and minor adjustments when using Colortune. Ran very well, but I foolishly increased the richness following a 2-3 CO reading, but only to 5.5 which is what these engines need to run well.
Very confusing

[christopher storey]

Is this when the engine is cold and choke is on ? If so, try putting the choke off ( at least to the "run" position in the mid part of its travel ) , as soon as the engine fires . If the car is only running on choke, then the sooty plugs are inevitable, and no real guide to that state of tune of the engine . 5.5% CO at hot idle is about correct

[jagman1970]

I had exactly the same problem about 2 years ago. The culprit was a faulty condenser.
Maybe try that. Good luck

Keith

[andrewh]

I would bet on ignition.

[chrisfell]

I’d be checking the floats and needle valves in the carbs.

[andrewh]

9 out of 10 carburettor faults are electrical!

[abowie]

Personally I don't think that if your CO reading of 5.5% was correct that that is the problem. Certainly, depending on the type of tester used the readings can be incorrect. The Gunson CO meter I use needs to be properly warmed up and calibrated before use otherwise the numbers are meaningless.
I would be checking to see if something has gone wrong with the choke. As suggested try starting without choke and see what effect this has.
In any event try putting the idle mixture back to where it was and see if this fixes it.