4k 5+5-fuel mixture adjustment then no cold start

[Archibald, Jon]

This car was running so rich, it had completely fouled the spark plugs.
After cleaning the plugs and turning the mixture screw until the black smoke
subsided, the car ran great, idled at the right speed, etc, and started 4
times with no problem. I let the car sit for about an hour and a half, then
tried to re-start. Nothing. Could leaning out the mixture control at the
sensor plate really render the car un-startable? I tried turning it back to
the rich-side, but still no go. I'm stumped.
TIA
Jon Archibald