Why would one cylinder on a Continental O-200 run cold at idle?
A: Idle circuit is set too lean and the cold jug is not firing.

B: Intake leak, causing same condition as A.

C: A little of both.

I know that a lot of people will lean out their idle mixture, by adjusting the screw on the carb, to reduce plug fouling with 100LL fuel (since leaning with the cockpit mixture doesn't do anything in the idle range).  You can tell when this has been done because the engine doesn't have the little RPM bump when pulling idle cutoff, and also it may require extra prime to keep running when cold.

Also, please write your questions with a bit of structure and grammar.  That stream of consciousness no-grammar style (that a lot of people use in emails out of laziness) is a total pain to read and interpret.