I recently acquired a '57 140. It starts great at ambient temps of 90+ Fahrenheit. Below that it will not start. Cold start solenoid clicks soundly. Tail pipes are VERY sooty; I once started it parked too far back in the garage and now have two big black smudges on the wall.



Temperature response says it is too lean. Tailpipe says it is too rich. Now what ??

 

Sounds like carbs/solenoid are not enrichening the mixture properly. I would remove the spark plugs and inspect them, as well as the cap/ rotor/points. Replace them as necessary. Then replace the solenoid next. Then rebuild the carbs.

 

I had the same issue with my XK140.
I removed the blowback valve from the enrichment device pipe, mounted on the underside of the inlet manifold where the pipe is mounted.
After that I never had a starting issue anymore.
Wonder if that valve is needed anyway, as the XK150 and 60th saloons do not have that anymore.

 

After fussing around, I finally went back to basics. Pulled the SU pistons - needles were set differently; one wrong, one very-very wrong. Set the jets to zero- significantly different number of turns on each, then backed out 3-1/2 turns. Then it started immediately when cold, with the solenoid disconnected at the 'Otter' valve. Further tweaking and it always starts great (though I have not yet had an opportunity to try at temps lower than 70F)