if it seems rich at idle this may be normal , I assume it has a lope to it at idle meaning it is dropping cylinders & pushing raw fuel into the exhaust so adjusting may not improve it .
adjusting the mixture is easy , make sure it is warm & at idle just turn in the mixture screws evenly approx 1/4 turn at a time until the engine idle drops then turn them back out just until the idle speed peaks turning it out more just wastes fuel
I do not know if you have the vacuum advance connected but typically with a build like you seem to have it will not help , disconnecting the vacuum advance & advancing the timing may significantly help the way the engine performs & idles